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kirza4 [7]
3 years ago
6

When cell's DNA duplicate? ​

Biology
2 answers:
g100num [7]3 years ago
4 0

Answer:

G1 phase causes the cell to grow in size and produce new organelles, which prepare for S phase, when the DNA replicates. Answer 3: Cells will duplicate or copy their DNA right before they divide. The process of cell division is called mitosis.

Explanation:

OleMash [197]3 years ago
3 0

The Synthesis Phase of the cell cycle is when DNA duplicates

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Explain how we know that DNA breaks and rejoins during recombination.
alisha [4.7K]

Answer:

It occurs through homologous recombination

Explanation:

GENERAL RECOMBINATION OR HOMOLOGIST

           Previously we defined its general characteristics. We will now describe a molecular model of this recombination, based on the classic Meselson and Radding, modified with the latest advances. Do not forget that we are facing a model, that is, a hypothetical proposal to explain a set of experimental data. Not all points of this model are fully clarified or demonstrated:

           Suppose we have an exogenote and an endogenote, both consisting of double helices. In recombination models, the exogenote is usually referred to as donor DNA, and the endogenote as recipient DNA.

1) Start of recombination: Homologous recombination begins with an endonucleotide incision in one of the donor double helix chains. Responsible for this process is the nuclease RecBCD (= nuclease V), which acts as follows: it is randomly attached to the donor's DNA, and moves along the double helix until it finds a characteristic sequence called c

Once the sequence is recognized, the RecBCD nuclease cuts to 4-6 bases to the right (3 'side) of the upper chain (as we have written above). Then, this same protein, acting now as a helicase, unrolls the cut chain, causing a zone of single-stranded DNA (c.s. DNA) to move with its 3 ’free end

2) The gap left by the displaced portion of the donor cut chain is filled by reparative DNA synthesis.

3) The displaced single chain zone of the donor DNA is coated by subunits of the RecA protein (at the rate of one RecA monomer per 5-10 bases). Thus, that simple chain adopts an extended helical configuration.

4) Assimilation or synapse: This is the key moment of action of RecA. Somehow, the DNA-bound RecA c.s. The donor facilitates the encounter of the latter with the complementary double helix part of the recipient, so that in principle a triple helix is formed. Then, with the hydrolysis of ATP, RecA facilitates that the donor chain moves to the homologous chain of the receptor, and therefore matches the complementary one of that receptor. In this process, the chain portion of the donor's homologous receptor is displaced, causing the so-called "D-structure".

It is important to highlight that this process promoted by RecA depends on the donor and the recipient having great sequence homology (from 100 to 95%), and that these homology segments are more than 100 bases in length.

Note that this synapse involves the formation of a portion of heteroduplex in the double receptor helix: there is an area where each chain comes from a DNA c.d. different parental (donor and recipient).

5) It is assumed that the newly displaced chain of the recipient DNA (D-structure) is digested by nucleases.

6) Covalent union of the ends originating in the two homologous chains. This results in a simple cross-linking whereby the two double helices are "tied." The resulting global structure is called the Holliday structure or joint.

7) Migration of the branches: a complex formed by the RuvA and RuvB proteins is attached to the crossing point of the Holliday structure, which with ATP hydrolysis achieve the displacement of the Hollyday crossing point: in this way the portion of heteroduplex in both double helices.

8) Isomerization: to easily visualize it, imagine that we rotate the two segments of one of the DNA c.d. 180o with respect to the cross-linking point, to generate a flat structure that is isomeric from the previous one ("X structure").

9) Resolution of this structure: this step is catalyzed by the RuvC protein, which cuts and splices two of the chains cross-linked at the Hollyday junction. The result of the resolution may vary depending on whether the chains that were not previously involved in the cross-linking are cut and spliced, or that they are again involved in this second cutting and sealing operation:

a) If the cuts and splices affect the DNA chains that were not previously involved in the cross-linking, the result will be two reciprocal recombinant molecules, where each of the 4 chains are recombinant (there has been an exchange of markers between donor and recipient)

b) If the cuts and splices affect the same chains that had already participated in the first cross-linking, the result will consist of two double helices that present only two portions of heteroduplex DNA.

8 0
3 years ago
Which of the following statements about ATP-powered pumps is NOT true? All ATP-powered pumps contain at least one transmembrane
MAVERICK [17]

Answer:

Only P-, F-, and V-class pumps transport ions.

Explanation:

The distinct classes of ATPases include:

1) Only the P-type ATPase actively transports ions across biological membranes. P-ATPases (also named E1-E2 ATPases) are found both in plasma and organelle membranes. These ATPases serve to transport ions and phospholipids by hydrolyzing ATP to ADP and phosphate.

2) A- and F-ATPases synthesize ATP by transforming the energy from a gradient of ions across the cell membrane.

3) V-ATPase (also known as Vacuolar-H+ ATPases) acidifies vacuole, lysosome, endosome and Golgi membranes. This type of ATPase couples the hydrolysis of ATP to the active transport of protons across biological membranes.

4) E-ATPases hydrolyze extracellular ATP.

5 0
3 years ago
What is cognitive therapy
alexandr1967 [171]

Answer:

cognitive therapy is a type of psychotherapy to treat human mood disorders such as depression.

hope it helps!

4 0
3 years ago
Read 2 more answers
Describe two types of evidence–other than the comparison of DNA sequences–that can be used to determine the phylogeny of organis
Lelechka [254]

Answer: Comparing the DNA sequence of the organisms can also tell you how closely related species they are. It can give you even more information since the original DNA is how the amino acid sequence of cytochromes is coded for.

Looking at embryonic development also helps you determine the phylogeny of organisms because a way an embryo develops can be very similar to the way another species develops but then both are full-grown they look very different and its tuff to explain how close they might be related

7 0
3 years ago
All sodium atoms have 11 protons in the nuclei of sodium Adams contains 12 neutrons and others contain 11 these different forms
Savatey [412]
Isotopes

Atoms of the same element; number of protons remain the same, number of neutrons vary. Chemical properties remain the same. Atomic mass varies.

Na sodium with 11 neutrons = atomic mass of 22

With 22 neutrons the mass is 23.

Both have 11 protons in the nucleus.
7 0
2 years ago
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