DNA Replication

Question 1

DNA Replication Synthesis (S) Phase Outline

Answer 1

Happens after interphase + before mitosis. Semiconservative replication (1 parent (/template) strand + 1 daughter strand (/mRNA))

Question 2

DNA Polymerase Outline

Answer 2

Synthesises new chains of nucleotides from free nitrogen base pairs. Reading parent strain in 3’-5’ and creating new strand in 5’-3’ direction by forming nucleotide phosphodiester bonds. Limitation; requires bases already present from primers (can’t synthesise new chain independently) and Mg as a cofactor

Question 3

DNA Helicase Outline

Answer 3

Breaks base pair H bonds of antiparallel strands (breaks helix). Forms replication forks

Question 4

Topoisomerase Outline

Answer 4

Enzyme regulates twisting of DNA in other regions then helicase is working on. Reducing tension, preventing braking. Known as DNA gyrase in bacteria

Question 5

3 Steps of Replication

Answer 5

Initiation, Elongation and Termination

Question 6

Transition of Free Nucleotide To Chain by DNA Polymerase

Answer 6

Free nucleotide; has 3 phosphate groups (catalysing large - charge). 3’ OH group is attached to a phosphate by DNA polymerase. Remaining 2 unbound phosphates are cleaved off

Question 6

DNA Ligase Outline

Answer 6

Joins Ozaki fragments together

Question 6

Primerase Outline

Answer 6

Adds free nucleotides to primer bases on DNA allows DNA polymerase to work.

Question 6

DNA Polymerase Proofreading

Answer 6

Incorrect base has weaker bonds (surrounding bases aren’t complementary), when nucleotide chain passes through enzyme, incorrect base sags and falls into DNA polymerase into exonuclease (chain slows down), exonuclease cleaves incorrect base. Loss of this function gives predisposition to cancer

Question 7

Initiation (Eukaryotes) Outline

Answer 7

Separation of double helix by helicase at A-T rich region (pro - 1 site, euk - +1 site). Topoisomerase elevates tension. 2 replication forks (bubbles) expand from point of origin in opposite directions

Question 7

Elongation (/Replication) (Eukaryotes) Outline

Answer 7

DNA polymerase builds new chains of nucleotides on leading (continuous) + lagging (ozaki fragmented) strands from RNA primers (layed by DNA primerase). New nucleotide chains are built in 5’-3’ direction. DNA ligase sticks fragments together

Question 7

DNA Polymerase Accuracy

Answer 7

Highly processive (rapid) and Highly accurate and proofreading

Question 7

What happens in cell if coding DNA is shortened

Answer 7

Cell cycle arrest and/or cell apoptosis

Question 7

What Is The Problem With Termination in The lagging Strand

Answer 7

When primases are removed after initial polymerase action, polymerase can’t fill in last 5’-3’ section of DNA leaving parental strand overhang (some coding DNA left non-transcribed)

Question 7

Termination (Eukaryotes) Outline

Answer 7

When replication forks collide from adjacent replicon

Question 8

Why is coding DNA more susceptible to degradation as we age

Answer 8

Telomerase loses function. Telomeres shorten, increasing risk of coding DNA degrading

Question 8

Telomerase Outline

Answer 8

Solution to lagging overhang. Extends parental strand with random nucleotides. Provides more space for primers to attach. Coding DNA is fully transcribed and telomere (buffers) are formed)

Question 8

Results of abnormally high telomerase function

Answer 8

Increased cell division = cancer

Question 8

Position of DNA strands in helix (relative to eachother)

Answer 8

Antiparallel (3’-5’ and 5’-3’). Either can be read in machine but scientific literature must explain direction of reslults’ reading