DNA and Replication Flashcards
In terms of DNA and RNA structure, what is a nucleotide?
A nucleotide is a sugar molecule bonded to phosphate group/s and a heterocyclic base
The leading strand of a DNA molecule has the following sequence:
5’-CGCATGTAGCGA-3’
What is the complementary sequence?
3’-GCGTACATCGCT-5’
In what direction does DNA polymerase synthesise DNA?
DNA polymerase can synthesize DNA in the 5’ to 3’ direction
What is the role of topoisomerases in eukaryotic DNA replication?
Topoisomerase enzymes cut, uncoil and reseal the double stranded DNA
Which of the following statements is true of DNA damage?
a) All DNA damage results in diseases such as cancer
b) Most DNA damage is repaired by the cell
c) All DNA damage is caused by physical, chemical or biological agents
d) Most DNA damage is advantageous to the cell
B
Give the name of the enzyme that creates a short RNA oligonucleotide at initiation sites where replication is to be carried out
Primase
Give the name of the enzyme that stitches Okazaki fragments together along the lagging strand
DNA Ligase
Give the name of the repeating DNA sequence at the end of chromosomes that prevents them from losing base pair sequences at their ends and from fusing together
A telomere
Give the name of the enzyme (made of proteins and RNA) that elongates chromosomes by adding TTAGGG sequences to the end of existing chromosomes
Telomerase
Which of the following correctly pairs the DNA replication enzyme with its function?
a) Topoisomerases work ahead of the replication fork to prevent supercoiling.
b) DNA polymerase I opens up the DNA at the replication fork.
c) Helicase seals gaps between DNA fragments.
d) DNA primase extends primers by adding nucleotides to the 3’ prime end.
A
Which of the following statements best explains the mechanism for DNA replication?
a) DNA replication is reductive, because half the total DNA present is copied.
b) DNA replication is semi-conservative, because each DNA strand serves as a template during replication.
c) DNA replication is dispersive, because the two resulting DNA molecules are mixtures of parent and daughter DNA.
d) DNA replication is conservative, because one resulting molecule is identical to the original and the other consists of two new strands.
B
Which of the following statements about these strands is true?
a) Okazaki fragments are used to synthesize the leading strand of DNA.
b) The leading strand of DNA is synthesized continuously.
c) DNA polymerase can only synthesize DNA on the leading strand.
d) The lagging strand can only be synthesized once the leading strand has been completed.
B
The molecular structure of DNA was first discovered by which two of the following?
a) Isaac Newton
b) James Watson
c) Francis Crick
d) Rachel Carson
B and C
Name the 4 Bases in DNA and which ones bond together and with how many hydrogen bonds
Adenine to Thymine - 2 Hydrogen Bonds
Cytosine to Guanine - 3 Hydrogen Bonds
What is different about the bases in RNA?
Thymine is replaces with uracil
In what direction is DNA synthesised?
5’ to 3’
Why does DNA Polymerase require a RNA primer to synthesize new DNA strands?
- DNA polymerase cannot initiate DNA chain synthesis on its own from the beginning
How is the leading and lagging strand synthesised using RNA Primer
The leading strand is synthesized continuously from a short single RNA primer which is about 10 nucleotides long in eukaryotes
The lagging strand is synthesised from multiple RNA primers that are formed periodically as each new region of the parental DNA duplex is unwound
Explain what Okazaki fragments are
Short DNA fragments that are synthesised sequentially and then joined up, named after discoverer Reiji Okazaki
Role of DNA Ligase and outline the steps
Seals gaps between the Okazaki fragments that are left in the lagging strand during DNA replication
Step 1 - DNA ligase uses ATP to activate the 5’ end at the DNA gap
Step 2 = A new phosphodiester bond is formed
Explain what Telomerase is
Telomerase is an enzyme that uses an RNA template to complete ends of chromosomes
Explain the role of topoisomerases
Prevent DNA tangling during replication. They are reversible nucleases that transiently break the phosphodiester bonds
What are the 2 types of topoisomerases?
Type 1 topoisomerases:
- Make nicks in one DNA strand and can relive supercoiling
- Make nicks in both DNA strands (double strand break). Can relieve supercoiling and untangle linked DNA helices
For DNA synthesis to take place the DNA double helix must be opened but it is very stable, how can the double helix be opened?
Very high temperatures
Proteins: DNA helicase and Single-stranded DNA-binding (SSB) proteins
What is the role of Single strand binding proteins?
Single strand binding proteins bind single stranded DNA (ssDNA) generated by helicases. They straighten and stabilise ssDNA, cooperating with the DNA polymerase
Name the 6 proteins involved in DNA replication
DNA polymerase
DNA Helicase
Topoisomerase
DNA primase
DNA ligase
Single strand DNA binding proteins
What happens if DNA replication goes wrong?
There are enzymatic mechanisms in place for correcting error:
- If the wrong nucleotide has been added by the polymerase, translocation of the enzyme to the next position along the template is inhibited. This pause provides the opportunity for a correction
- DNA polymerase exhibits proofreading activity in which an incorrectly paired nucleotide is removed through exonuclease activity.
- The cell has other DNA repair mechanisms
