Question

Elements Tables Charts SmartArt Raview Normal No Spacing Headingt Text Bax Shape Illustrate the enzymatic processes of DNA replication, repair, and recombination Explain the processes that control RNA synthesis and maturation Explatn the translation of mRNA into functioning proteins by ribosomes and tRNA 2 3 4 9

Answer 1

DNA replication is the process by which DNA makes a copy of itself during cell division.

1. The first step in DNA replication is to ‘unzip’ the double helix structure of the DNA? molecule.
2. This is carried out by an enzyme? called helicase which breaks the hydrogen bonds? holding the complementary? bases? of DNA together (A with T, C with G).
3. The separation of the two single strands of DNA creates a ‘Y’ shape called a replication ‘fork’. The two separated strands will act as templates for making the new strands of DNA.
4. One of the strands is oriented in the 3’ to 5’ direction (towards the replication fork), this is the leading strand?. The other strand is oriented in the 5’ to 3’ direction (away from the replication fork), this is the lagging strand?. As a result of their different orientations, the two strands are replicated differently
5. Numerous RNA primers are made by the primase enzyme and bind at various points along the lagging strand.
6. Chunks of DNA, called Okazaki fragments, are then added to the lagging strand also in the 5’ to 3’ direction.
7. This type of replication is called discontinuous as the Okazaki fragments will need to be joined up later.
8. Once all of the bases are matched up (A with T, C with G), an enzyme called exonuclease strips away the primer(s). The gaps where the primer(s) were are then filled by yet more complementary nucleotides.
9. The new strand is proofread to make sure there are no mistakes in the new DNA sequence.
10. Finally, an enzyme called DNA ligase seals up the sequence of DNA into two continuous double strands.
11. The result of DNA replication is two DNA molecules consisting of one new and one old chain of nucleotides. This is why DNA replication is described as semi-conservative, half of the chain is part of the original DNA molecule, half is brand new.
12. Following replication the new DNA automatically winds up into a double helix

Repair :Most mistakes during replication are corrected by DNA polymerase during replication or by post-replication repair mechanisms.

The enzymes recognize the incorrectly-added nucleotide and excise it; this is then replaced by the correct base. If this remains uncorrected, it may lead to more permanent damage. How do mismatch repair enzymes recognize which of the two bases is the incorrect one? In E. coli, after replication, the nitrogenous base adenine acquires a methyl group; the parental DNA strand will have methyl groups, whereas the newly-synthesized strand lacks them. Thus, DNA polymerase is able to remove the incorrectly-incorporated bases from the newly-synthesized, non-methylated strand. In eukaryotes, the mechanism is not very well understood, but it is believed to involve recognition of unsealed nicks in the new strand, as well as a short-term continuing association of some of the replication proteins with the new daughter strand after replication has been completed.

the fork moves au veplication takes 3old strand 5 old strand 3'we strand 3'old styaud euplicahon 5'old ctrand -fork

In bacteria, RNA transcripts are ready to act as messenger RNAs and get translated into proteins right away. In eukaryotes, things are a little more complex, though in an pretty interesting way. The molecule that's directly made by transcription in one of your (eukaryotic) cells is called a pre-mRNA, reflecting that it needs to go through a few more steps to become an actual messenger RNA (mRNA). These are:

• Addition of a 5' cap to the beginning of the RNA

• Addition of a poly-A tail (tail of A nucleotides) to the end of the RNA

• Chopping out of introns, or "junk" sequences, and pasting together of the remaining, good sequences (exons)

Once it's completed these steps, the RNA is a mature mRNA. It can travel out of the nucleus and be used to make a protein.