Flashcards in Maintanence and Use of Genetic Information Deck (47):
What are the letters of the X4 stages of the cell cycle?
G1 (Growth 1)
S (DNA Synthesis)
G2 (Growth 2)
At which part of the cell cycle is a signal received to replicate DNA?
What happens if no signal is received in G1 instructing the cell to replicate its DNA?
The cell enters a quiescent state (G0) where it exists but does not divide.
Which phases of the cell cycle are interphase?
G1, S, and G2.
Explain in basic terms the process of semi-conservative DNA replication.
The DNA unwinds to expose its base pairs, which are used as a template for the daughter strands to be synthesised from. This utilises complementary base pairing.
What is the name of the specific points on genomes at which replication begins?
Origins of replication .
What is the name of the area of unwound DNA which is the site of DNA replication?
What is the prong like structure at the replication bubble called?
Replication fork (X2 formed).
What is the name of the enzyme which unwinds DNA ready for replication?
A broken double helix may instantly reform, if it wasn’t for which structures?
Single strand binding proteins.
What is the name of the process of intense chromatin coiling of a remaining DNA helix following the separating of its strands via DNA helicase?
What does topoisomerase do in DNA replication?
Acts above the replication fork to break some phosphodiester bonds, providing the helix with a degree of freedom to avoid positive supercoiling.
From which end/directions does DNA polymerase work to synthesise new daughter DNA strands?
ONLY in the 5-prime to 3-prime direction.
What is the name of the strand of DNA replication that is synthesised continuously?
The leading strand.
What is the name of the strand that is synthesised discontinuously?
The lagging strand.
Out of DNA polymerase and RNA polymerase, which can initiate synthesis of (DNA/RNA) and which can only add nucleotides to a pre-existing chain?
DNA polymerase = can only add nucleotides to existing chains
RNA polymerase = can initiate RNA synthesis
What is the name of the multiple sections of daughter strand DNA created by the lagging strand of DNA replication?
DNA synthesis starts with the synthesis of a primer of what?
Which enzyme is involved in this process?
A short RNA primer.
Primase (a type of RNA polymerase)
Each lagging strand fragment will have an RNA primer. These need to be degraded, but by which enzyme?
Which enzyme joins the two fragments of lagging strand DNA once their RNA primers have been removed?
What process sees the lagging strand bend around to co-ordinate DNA synthesis in the same direction despite opposing topological directions.
The formation of a lagging strand loop.
What is the role of HELICASE?
Unwinds the DNA strands ready for replication.
What is the role of TOPOISOMERASE?
Releases the positive supercoiling of DNA.
What is the role of SINGLE STRAND BINDING PROTEIN?
Stops unwound DNA from reforming a double helix.
What is the role of PRIMASE?
Forms a RNA primer which allows DNA synthesis to begin.
What is the role of EXONUCLEASE?
Removes RNA primer from each Okazaki fragment.
What is the role of DNA polymerase?
What is the role of DNA ligase?
Links adjacent Okazaki fragments once Exonuclease has removed their RNA primers.
In which direction does DNA polymerase degrade DNA?
3-prime to 5-prime, as it contains an exonuclease.
What does DNA polymerase do when a wrong base is added during replication?
Rate of synthesis will slow, activating the DNA polymerase exonuclease which will undo the fault, allowing DNA synthesis to continue correctly.
What is the end replication paradox?
This is the name given to the loss of the ends of linear chromosomes after each round of replication due to DNA polymerase ability to only extend from the 5-prime to 3-prime direction.
Which structures prevent the end replication paradox?
Which enzyme catalyses the synthesis of telomeres?
How do telomeres work?
Extend the DNA without a chromosomal template to prevent loss of information due to the end replication paradox.
What combination of bases is repeated to form the composition of telomeres?
(5-prime) TTAGGG (3-prime)
In which cells are telomeres active, and in which are they not?
Active within gametes.
Inactive within somatic cells.
What type of mutation involves a single base being changed, and how many types of this mutation are there?
What are the X3 types of point mutation?
Silent mutations (synonymous)
Missense mutations (non-synonymous)
What is a silent mutation?
A form of point mutation which does NOT result in a different amino acid being coded for.
E.g. CGA (arg) — CGG (arg)
What is a missense mutation?
A form of point mutation which results in a DIFFERENT amino acid being coded for.
E.g. GAG (Glu) — GTG (val)
What is a nonsense mutation?
A form of point mutation which results in a STOP codon being coded for.
E.g. TGC (cys) — TGA (stop)
What is an INDEL?
A small insertion or deletion of bases in a DNA sequence.
How many base pairs would be needed in an INDEL to maintain a reading frame?
A multiple of X3.
Name X4 other types of mutations that involve larger chunks of chromosome DNA and describe what they do.
Inversions (a section of DNA flips itself around)
Deletions (a section of DNA deletes itself)
Duplications (a section of DNA duplicates)
Translocations (a section of DNA moves to a different place along the chromosome)
Name X3 ways spontaneous mutations can occur.
Errors in DNA replication
- these have escaped proof reading and repair mechanisms
- the gain or loss of repeated triplets of bases in areas of many repeats due to the repeating unit’s ability to ‘slide’ over each other and still retain complementary base pairing. Can occur in the forwards (occurs to parents, strand and leads to n and n-1 strands on second replication) or backwards (occurs in daughter strand and leads to n and n+1 strands on second replication) direction.
- cysteine loses an amino group to become uracil. This changes a C-G pairing to an A-T pairing.
Name X2 ways in which induced mutations occur.
- UV light (UV-B) indices a chemical bond between adjacent thymines (making thymine dimers) which distorts DNA and interferes with replication.
- ionising radiation causes strand breaks.
Some agents react with bases:
- nitrous acid = cytosine - uracil
- alkylating agents = guanine modifiers
- free radicals = break strands