Which of the following statements about the basic structural features of DNA are true? Select all true statements. Select all true statements. The major and minor grooves prevent DNA binding proteins from making contact with nucleotides. In a DNA macromolecule, the two strands are complementary and antiparallel. The twisting of the DNA double helix is attributed to the tight packing of DNA bases and base-stacking. The major and minor grooves form in the DNA helix because the DNA strands are antiparallel.

Answer:

The oxygen dissociation curve for hemoglobin is sigmoidal where as for myoglobin it is hyperbolic.

Explanation:

Oxygen dissociation curve: A graphical representation of relationship between partial pressure of O2 and percentage saturation of hemoglobin with oxygen is known as O2-dissociation curve. It is sigmoidal or S- shaped curve. The amount of O2 that can bind with Hb is determined by partial pressure of oxygen. The percentage of Hb that is bound with O2 is called percentage saturation of Hb.

In human adults, at pO2 of 25 mm of Hg the hemoglobin is 50% saturated with oxygen. This partial pressure is called P-50.

Hemoglobin shows S shaped curve due to cooperative binding of oxygen that is binding of first oxygen increases the ability of second oxygen binding and so on. One Hb can carry 4 oxygen molecules.

In case of myglobin, it has more affinity for oxygen but it has only one Fe+2 group, there is no cooperative binding. The curve obtained will be hyperbolic than being sigmoid.

Please find the attached image which shows both the curves. (Image reference: Evolution of Myoglobin and Hemoglobin ; Author and Curator: Larry H. Bernstein, MD, FCAP )

Since myoglobin has more affinity for oxygen its P-50 value is less, that is at low partial pressure of oxygen myoglobin gets 50% saturated. But the P-50 value for hemoglobin is high which means comparatively more partial pressure of O2 is needed for hemoglobin to be 50% saturated.

Answer:

The exons may be defined as the coding region of the RNA that codes for the particular amino acid. The introns are the non coding region of RNA and must be removed in the final RNA product.

Exon shuffling result in the formation of new gene. The alteration of the exon and intron structure leads to the new gene function in evolution. The genes that are favored and conserved in the evolution perform new gene function. The genes that are selected against are deleted during the evolution.

The exon/intron structure in genes facilitates the evolution of new functions through exon shuffling, alternative splicing, and gene duplication, significantly contributing to genetic diversity and adaptability.

The exon/intron structure of genes is pivotal in the evolution of new gene functions. Introns, which are non-coding sequences, serve as a buffer against deleterious mutations, and through unequal recombination during meiosis, they can lead to gene duplication and exon shuffling. This occurrence can result in new proteins with additional structural domains and functions, contributing to genetic diversity and evolutionary progress.

Exon shuffling is a mechanism by which exons can be mixed and matched between genes, potentially creating proteins that carry out new functions. Additionally, introns and their associated sequences play a crucial role in alternative splicing, which allows for the production of multiple protein variants from a single gene, further increasing the potential for diversity and adaptability.

Gene duplication, which can occur due to non-homologous recombination facilitated by introns, allows one gene copy to accumulate mutations while the other maintains its original function. This duplicated gene can then evolve over time, adding to the pool of selectable DNA sequences and leading to an increase in species diversity and evolutionary innovation.

Answer:

Option (d).

Explanation:

Mutation may be defined as the sudden, heritable change in the nucleotide sequence of the organism. Mutation may occur due to the errors in DNA replication or may occurs due to the mutagens.

Joshua and Lederberg experiment explains that mutation is the non adaptive and random process that occur in the organism. He used the replica plating of E.coli and grows them on streptomycin drug. The bacteria was grown on the the primary plate and they are transferred to the secondary plate with streptomycin drug in the growth environment. The resistant strain of bacteria grows in the streptomycin environment.The pattern of bacteria growth on the plate explained that mutation occurs randomly and it is a non adaptive process.

Thus, the correct answer is option (d).

Answer:

d. the 5' end

Explanation:

Capping is a co-transcriptional modification made to RNA in the nucleus after the first 25–30 nts are incorporated into the nascent transcript, which is synthetized in the 5' ---> 3' direction.

The cap consists of a methylated guanosine nucleotide added to the 5' end of the new mRNA transcript, and is important for several processes, which include:

Answer:

E. It takes a picture of the brain according to oxygen levels. More oxygen in an area indicates more activity in that area.

Explanation:

Haemoglobin is diamagnetic when oxygenated but paramagnetic when deoxygenated. This distinction in magnetic characteristics leads to tiny variations in the blood MR signal. Since blood oxygenation differs, these variations can be used to identify brain activity depending on the concentrations of neural activity.

Answer:

b. the rate at which the mRNA is degraded.

Explanation:

DNA is transcribed into mRNA which then joins ribosomes present in the cytoplasm to serve as a template for protein synthesis. Regulation of gene expression occurs at several levels.

One such regulatory mechanism is the stability of mRNA and the rate of its degradation which in turn affects the availability of template for the process of protein synthesis and thereby keeps a check on the total amount of protein being formed in a cell.

For example, a very short life span of bacterial mRNA (few minutes) allows them to regulate the pattern of protein synthesis quickly in response to the changes in surroundings.

The amount of protein synthesized from an mRNA molecule is influenced by the rate of mRNA degradation, which affects its stability and the duration of its presence in the cytoplasm for translation.

b is correct

The amount of protein made using a given mRNA molecule within a cell depends on several factors, one of which is the rate at which the mRNA is degraded. mRNA carries the genetic message from the DNA during the process known as transcription, and it dictates the synthesis of proteins through translation in conjunction with ribosomes and other cellular machinery.

The mRNA is short-lived, and its stability in the cytoplasm is crucial as it influences the amount of time available for translation. A longer mRNA lifespan allows for more protein production. Thus, the correct answer to the student's question is option b. the rate at which the mRNA is degraded.

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Answer:

The correct answer is D) photolysis

Explanation:

Photolysis is a process in which light energy is used by photosystem II to split water which generates oxygen, H⁺ions end electrons. oxygen is released in the atmosphere and inhaled by animals and electrons are used to generate energy.

The electron released by the splitting of water is transferred to the first electron acceptor called pheophytin. This electron is passed through a series of complex and produce energy in the form of ATP and NADPH.

The process of photolysis does not occur in photosystem I because lysis of water takes place and electron is passed from photosystem II to photosystem I.

Photolysis is not directly associated with Photosystem I. Instead, it's a process that occurs in Photosystem II, where water molecules are broken down into oxygen, protons, and electrons.

The correct answer is D) photolysis. Photosystem I is a protein complex involved in the light-dependent reactions of photosynthesis. Its primary functions include harvesting light energy by chlorophyll (option A), receiving electrons from plastocyanin (option B), possessing a reaction center known as P700 (option C), and passing electrons to ferredoxin (option E).

In contrast, photolysis - the breaking down of molecules using light - is not directly associated with Photosystem I, but instead with Photosystem II, where water molecules are broken down into oxygen, protons, and electrons.

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Semen does not contain substances to lower the pH of the uterine environment.

The correct answer is D. Substances to lower the pH of the uterine environment.

Semen is the fluid that contains sperm, which is released during ejaculation. It contains various components that help sperm in their journey to fertilize an egg. These components include fructose (a sugar that provides energy for sperm), mucus (which helps with the motility of sperm), clotting enzymes (to prevent semen from leaking out of the vagina), and an active cot-dissolving enzyme (to break down the mucus in the cervix).

However, semen does not contain substances to lower the pH of the uterine environment. This is because the female reproductive tract naturally provides an optimal pH for sperm survival without the need for additional substances in semen.

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Answer:

False

Explanation:

Approximately 200 out of 200 million sperms ejaculated during intercourse reach the general vicinity of the egg.  They sperms must undergo capacitation during which dilute inhibitory factors fluids of the female reproductive tract weaken the membrane of the sperm head so that head of the sperm can be broken easily when it came in contact with the egg.

The first sperm to reach an egg isn’t the one to fertilize it because the egg is surrounded by a gelatinous membrane called the zona pellucida. Outside this layer, a layer of small granulosa cells also present.

Therefore, it requires numerous sperm to clear a path through these barriers before one of them can penetrate the egg and fertilize it.

Answer:

The correct answer is D.

Explanation:

Proto-oncogenes code for proteins that usually help to regulate cell growth and differentiation.

If they acquire a mutation, they become oncogenes and therefore can induce cancer.

Additionally, if they increase the amount of certain proteins concentration or acquire chromosomal translocations they can also become oncogenes.

Answer:

Neurally

Explanation:

Cardiac regulation is controlled neurally. The nervous systems receive signals regarding the condition of the circulatory system. Different receptors receive different type of signals. For example, the baroreceptors, receive information about the blood pressure, the chemoreceptors sends and codify information about the CO2, O2 and PH concentration in the bloodstream.

All of these signals are processed and analyzed by a group of neurons in the spinal bulb in the brain. This particular region of the brain, produces signals that travel trough neurons until the nerve supply of the heart and the smooth muscles (of veins and arterioles) to control the blood pressure and cardiac output.

"The circulatory system is controlled through both hormonal and neural mechanisms.

Neurally, the circulatory system is regulated by the autonomic nervous system (ANS), which includes the sympathetic and parasympathetic branches. The sympathetic nervous system, when activated, increases heart rate, cardiac output, and the force of cardiac muscle contractions, thereby increasing blood pressure. This response is part of the ""fight or flight"" reaction. Conversely, the parasympathetic nervous system decreases heart rate and promotes relaxation, which is part of the ""rest and digest"" response.

Hormonally, several key hormones play a role in regulating the circulatory system:

1. Epinephrine and Norepinephrine: Released by the adrenal medulla, these hormones increase heart rate and the force of cardiac contractions, similar to the sympathetic nervous system's effects.

2. Atrial Natriuretic Peptide (ANP): Secreted by the atria of the heart in response to stretching due to increased blood volume, ANP promotes excretion of sodium and water by the kidneys, which in turn reduces blood volume and pressure.

3. Renin-Angiotensin-Aldosterone System (RAAS): When blood pressure drops, the kidneys release renin, which leads to the production of angiotensin II. Angiotensin II is a potent vasoconstrictor that increases blood pressure. It also stimulates the release of aldosterone from the adrenal cortex, which promotes sodium and water retention by the kidneys, further increasing blood volume and pressure.

4. Antidiuretic Hormone (ADH): Also known as vasopressin, ADH is released by the posterior pituitary gland in response to increased plasma osmolality or decreased blood volume. ADH increases water reabsorption in the kidneys, which increases blood volume and pressure.

5. Endothelins: These are a group of peptides produced by the endothelial cells lining the blood vessels. They are among the most potent vasoconstrictors known and play a role in regulating vascular tone and blood pressure.

 These hormonal and neural controls work in concert to maintain homeostasis in the circulatory system, ensuring that blood flow and pressure are adjusted according to the body's changing needs."

Answer:

The correct option is: b. attenuated vaccine

Explanation:

FluMist is the trade name of the live attenuated influenza vaccine, manufactured by MedImmune. This vaccine is used for the prevention of influenza, also called flu.

It is an attenuated vaccine which is given in the form of nasal spray.

An attenuated vaccine alters the pathogen by reducing its virulence and makes it harmless.

Answer:

False

Explanation:

Facultative anaerobes are organisms that can grow in both the presence or absence of oxygen.

Organism that suffer a poisonous reaction or that can't live in the presence of oxygen are called obligate anaerobes.

Answer:

False.

Explanation:

Tolerance is when, after being exposed to a certain drug for a long period of time, the body can no longer respond to the same dose that used to trigger a biological response, so the dose has to be increased.

Answer: There are 4¹⁰⁰ possible strands, approximately 1.61x10⁶⁰

Explanation:

This is a combinatorics problem. Each nucleotide has the possibility of being one of the four common nucleotides, adenine (A), guanine (G), thymine (T) and cytosine (C).

If the strand would be 1 nucleotide long, the possibilities would be 4, one for each possible nucleotide. If the strand would be 2 nucleotides long, for each nucleotide on the first position there would be four possible nucleotides on the second position, giving 4x4=4²=16 possible strands.

For 3 nucleotides long you have 4 possible nucleotides for each of the 2-nucleotide-long strands, 4x4x4=4²=64 possible strands. Following that pattern, for a 100 nucleotide long DNA strand, there would be 4x4x...x4x4=4¹⁰⁰ possible strands.

Answer:

a. DNA polymerase proofreading:   consequence of its absence is the DNA mutation

b.  Mismatch repair enzymes : consequence of its absence impedes homologous recombination resulting in the final mutation

c. Nucleotide excision repair enzymes : the absence of nucleotide cleavage repair enzymes would impede the functioning of damaged DNA repair mechanisms

Explanation:

a. DNA polymerases are the enzymes that form the DNA in cells. During DNA replication (copying), most DNA polymerases can "check their work" with each base they add. This process is called review. If the polymerase detects that you have added a wrong nucleotide (incorrectly paired), remove it and replace it immediately, before continuing with DNA synthesis

b. In homologous recombination, the information from the homologous chromosome that matches that of the damaged one (or from a sister chromatid if the DNA has been copied) is used to repair the fragmentation. In this process the two homologous chromosomes are approached and the undamaged region of the homologue or the chromatide is used as a template to replace the damaged region of the broken chromosome. Homologous recombination is "cleaner" than the union of non-homologous ends and does not usually cause 11 mutations

c. Excision repair: damage to one or a few DNA bases is usually fixed by removing (excising) and replacing the damaged region. In repair by base cleavage, only the damaged base is removed. In nucleotide excision repair, as in the mating repair we saw earlier, a nucleotide section is removed

The absence of DNA repair mechanisms such as DNA polymerase proofreading, mismatch repair enzymes, and nucleotide excision repair enzymes can lead to an elevated mutation rate, causing genomic instability and increasing the risk of cancer and genetic disorders.

Consequences of Missing DNA Repair Mechanisms

The integrity of DNA is safeguarded by various repair mechanisms. When these systems fail or are absent, the stability and function of an organism's genome are compromised. Here's what happens when certain DNA repair mechanisms are missing:

DNA polymerase proofreading: DNA polymerase adds nucleotides during DNA replication and conducts proofreading to ensure accuracy. If proofreading is compromised, incorrect bases may be incorporated, resulting in mutations which can lead to cancers or other genetic disorders.

Mismatch repair enzymes: These enzymes correct errors that escape proofreading during replication. Without mismatch repair, these errors become permanent, increasing mutation rates and contributing to diseases like cancer.

Nucleotide excision repair enzymes: These enzymes repair bulky lesions such as thymine dimers which are primarily caused by UV light. Absence of these enzymes may lead to a higher incidence of skin cancer due to the accumulation of these lesions.

In summary, the lack of these DNA repair mechanisms can result in increased mutation rates, leading to genomic instability, and may significantly raise the risk of cancer and other hereditary diseases.

Answer:

In eukaryotic cells you find core and proximal promoters.

Promotors are specific DNA sequences where transcription factors (proteins) and RNA polymerase binds to initiate transcription. Promotors are located upstream the coding sequence

Core promoters are where RNA polymersae binds and proximal promoters are where transcription factors bind.

Enhancer elements are DNA sequences where transcription factors (proteins) bind to increase the rate of expresion of an specific gene. Enhancers can be located either upstream,  downstream or thousands of nucleotids away  from the of the coding region.

Explanation:

Promoters and enhancer are key elements for controling gene regulation. Transcription begins when chromatin rearranges from a condensed state to a accesible state, this allow to transcrition factors and RNA polymerase to  bind specif DNA sequences (promotors).  Proteins bind to enhancers , this complex develops a DNA loop, so that the protein that is bound to the enhancer interacts with the RNA polymersase. When this interaction is made, the activity of the RNA polymerase is increased.

Answer:

Three dangerous recreational drugs: crack cocaine, heroin, methamphetamines

Explanation:

Recreational drugs are the psychotropic drugs that induce an intoxicating effect. The three types of recreational drugs are depressants, stimulants, and hallucinogens.

The drugs affect the nervous system and induce hallucinations, euphoria, enhanced alertness and locomotion, low blood pressure, anesthesia, analgesia and memory impairment.

Some of the dangerous recreational drugs are crack cocaine, heroin, methamphetamines and alcohol.

Answer:

Endocrine  :

Endocrine cells may be defined as the cells that helps in  the cell signalling in which the cells are located far apart. The product can shows slow effect but long lasting effect.

Paracrine:

Paracrine cells may be defined as the cells that are involved in the paracrine signalling. They acts on the cells that are located close to each other and generates quick response in body.

Autocrine :

Autocrine cells that are involved in the autocrine signalling affect their own cells. The target and signalling cells are same in autocrine. The pain sensations of the body are also regulated by autocrine signalling.

Final answer:

Endocrine, paracrine, and autocrine are types of cell signaling. Endocrine signaling travels long distances through bodily fluids, paracrine signaling acts locally between neighboring cells, and autocrine signaling occurs when a cell responds to its own signals.

Explanation:

In multicellular organisms, cells communicate through different types of signaling. The three main types are endocrine, paracrine, and autocrine signaling, each differing primarily in the distance the signal travels to reach the target cell.

Endocrine signaling involves hormones secreted into the extracellular fluid that then diffuse into the blood or lymph to travel to distant cells throughout the body. An example of endocrine signaling is the secretion of hormones by the pituitary gland.

Paracrine signaling involves signals, or paracrine factors, that act locally between cells that are close together. These signals move by diffusion through the extracellular matrix and are generally quickly degraded or removed to maintain localized effects. Histamine, responsible for the immune response in asthma, is an example of a paracrine signal.

Autocrine signaling occurs when a cell responds to signals it releases itself, with interleukin-1 (IL-1) being an instance of an autocrine involved in inflammatory responses. Autocrine signaling can also influence nearby similar cells and plays a key role in the early developmental processes and programmed cell death.

Answer: True

Explanation:

The ear is a organ found in the body of mammals and other animals that helps in hearing.

The ear consists of outer part and inner part. The outer part of the ear converges the sound waves and the transfers to the ear canal.

The sound is then amplified inside the ear and we hear sound. There is a fluid which is found inside the inner ear contains a fluid that helps in balancing of the body.

Answer:

Spores are made by the millions, so some of them are likely to land in a good place to grow. Spores are lightweight and can drift around on the slightest air currents, so spores are spread far and wide. Spores have hard outer coverings to protect them until they begin to grow.

Explanation:

Answer:

Capillaries are the smallest-diameter blood vessels that connect the smallest arterioles to the smallest venules, they have sphincters to control the blood distribution, based on the body's demands, the can relax or constrict so the blood can follow specific pathways to meet the tissue's necessities.

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Answer:

C Patterns

Explanation:

got 100 on quiz

The shell of the chambered nautilus the seeds in a sunflower and pineapples all exhibit a structure called the "Fibonacci spiral". This phenomenon represents the pattern phenomena by cross-cutting.

A series of numbers in which every number is the sum of the two its previous numbers Fibonacci spiral. It starts at  0 and 1, the sequence: 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, and goes on forever. Xn+2= Xn+1 + Xn is the mathematical equation that is used to describe or represent the  Fibonacci sequence.

Several people have claimed that there are many special properties of this numerical sequence. They say that it is “nature’s secret code” for the construction of perfect structures. Some examples given are the Great Pyramid at Giza and the iconic shape of the seashell that is used as the cover of most mathematical textbooks. But most of these assumptions are incorrect.

Therefore, this is a pattern phenomenon represented by cross-cutting.

Read more about the Fibonacci spiral, here

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The correct answer is A. A sperm

Explanation:

Sperms are a type of reproductive cells that are essential for sexual reproduction. Sperms are male reproductive cells different from eggs that are female cells. Additionally, these can have flagella that allow them to move to reach the egg or be non-motile. In the case of human sperms, these have a flagella and also they contain 23 chromosomes; additionally, in this there is 1 allosome chromosome that defines sex and in males and therefore sperms can be either X or and 22 autosomes that refer to chromosomes not related to sex, this is also particular from sperms as eggs in humans can only have an X allosome. According to this, it is a sperm the cell that contains 22 autosomes and a Y chromosome.

Answer:

mCNS and PNS.

Explanation:

Nervous system of the body includes all the the nerves that carry message in the body from the spinal cord and brain  . Nervous system has divided into two main branches.

The two main divisions of the nervous system are peripheral nervous system (PNS) and central nervous system (CNS). The central nervous system constitutes of the spinal cord and brain. The peripheral nervous system include the sensory receptor, motor nerves and sensory neurons.

Thus, the correct answer is option (b).

The two principal parts of the nervous system are the Central Nervous System (CNS) and the Peripheral Nervous System (PNS). The CNS is the main command system for the body, while the PNS is responsible for transmitting messages to various body parts.

The two major divisions of the nervous system are the Central Nervous System (CNS) and the Peripheral Nervous System (PNS). The CNS includes the brain and spinal cord, and it is the primary command center for the body. The PNS includes all the nerves that branch out from the brain and spinal cord and extend to other parts of the body such as muscles and organs. These two divisions work together to transmit and process information to respond to stimuli from both internal and external environments.

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Answer:

Yes they are polymers of monosaccharides.

Explanation:

Disaccharides are polymers of monosaccharides, which are simple sugar molecules such as glucose. Monosaccharides, monomers, are linked by glycosidic bonds to make disaccharides.

Example; the linkage of glucose and fructose to make sucrose.

Answer:

Metoclopramide is a drug widely used for its antiemetic effect (that is, used for the symptomatic treatment of nausea and vomiting). Its adverse reactions are varied, affecting even the central nervous system, causing extrapyramidal syndromes.

Explanation:

Due to the antidopaminergic action of metoclopramide. Signs and symptoms can range from spasms of the muscles of the face, neck or tongue, motor agitation and tremor, acatisia (feeling restless and in need of constant movement) and acute dystonic reactions. Extrapyramidal syndrome is transient and disappears after eliminating or decreasing the dose of metoclopramide.

Metoclopramide is a drug that can be administered intravenously. Its administration can be in bolus or by a continuous infusion. Is there any method of choice to prevent or reduce the occurrence of pyramidal syndromes?

A recent systematic review concluded that, compared with bolus administration, continuous intravenous infusion of metoclopramide reduced the occurrence of extrapyramidal side effects.

With this gesture we can perform quality care and try to avoid side effects to our patients.

Answer:

The correct answer is option C.

Explanation:

On the basis of Chargaff's rule, adenine always base pairs with thymine, and guanine always base pairs with cytosine. This rule is also called complementary base pairing. By following this rule, the DNA polymerase can produce the new strand of DNA easily.  

It utilizes the old strand of DNA as a template and produces the new one by opting for the accurate nucleotide on the basis of the template strand. Thus, the correct answer is option C, that is, the base pairs, which make up the center of the molecule of DNA will only match up C with G and A with T.  

Answer:

The correct answer is option D. True tissues.

Explanation:

The cell that made sponge does not form the tissue however sponge have cells that play important role and specific for specific function but does not have true tissues.

In other animal phyla cells form tissue or organ or organ systems and called as true tissues.

Thus, the correct answer is option D. True tissues.

It is mainly based on the true tissues.

Sponges are the multicelled organism of the phylum Porifera. The body of the sponges has various channels and pores, that allows water circulation.  

Sponges are multicellular organism that consists of pores and channels in their body for water circulation and lacks specific tissues. They have cells assigned with specific roles and functions but lack true tissues unlike animals of the other phyla.

The animals of the various phylum are classified based on the body cavity, tissues, symmetry,  fate of the blastopore.

Therefore, option d. is correct.

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In the cell cycle, G1 is the phase when the cell has the least amount of DNA. This DNA is duplicated during S phase, meaning the cell has twice as much DNA in the G2 phase. So, if Cell A has half as much DNA as cells B, C, and D, then Cell A is likely in the G1 phase.

In the cell cycle, the amount of DNA a cell has can help determine which phase it is in. The cell cycle consists of interphase (G1, S, and G2 phases), and the mitotic phase (including prophase, metaphase, anaphase, and telophase). During the G1 phase of the cell cycle, a cell has the least amount of DNA because it hasn't duplicated its DNA yet. DNA replication occurs during the S phase, so by the G2 phase, the cell has twice as much DNA as it did in G1. Thus, if Cell A has half as much DNA as cells B, C, and D in a mitotically active tissue, Cell A is most likely in the G1 phase.

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Cell A is most likely in the G1 phase of the cell cycle, a stage prior to DNA synthesis, as it has half the amount of DNA than cells B, C, and D, which presumably already completed the S phase (DNA replication).

Cell A is most likely in the G1 phase of the cell cycle. The G1 phase is a period in the cell cycle during interphase, before DNA synthesis (S phase). In G1 phase, the cell synthesizes mRNA and proteins in preparation for subsequent steps leading to mitosis. At this stage, it has half as much DNA as it will have after it completes the S phase. Therefore, cells B, C, and D, each having twice as much DNA, are probably in the G2 phase, metaphase, or any phase after DNA replication (S phase) happened, during which the amount of DNA in the cell has already been doubled.

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