L10 Nucleic Acids and DNA Replication Flashcards
__?__ are the fundamental biochemical building block of DNA and RNA
Nucleotides
Nucleotides are composed of three components:
- __1__ base: pyrimidine (C, U, T) or purine (G, A)
- __2__ : deoxyribose in DNA, ribose in RNA
- __3__ group: acts as a bridge between adjacent ribose/deoxyribose groups
1) Nitrogenous
2) Pentose sugar
3) Phosphate
Adenosine is the __?__ (sugar + base) component of ATP
nucleoside
True or false: in DNA a pyrimidine always pairs with a purine?
True
C (pyrimidine) and G (purine)
T (pyrimidine) and A (purine)
Nucleotides are always added to the __?__ end of a polynucleotide chain
3’
When adding a new nucleotide to a polynucleotide chain, the __1__ of the new nucleotide reacts with the __2__ of the polymer to a __3__ bond. The chain grows in a __4__ to __5__ direction.
1) alpha-phosphate
2) 3’-OH group
3) 3’-5’ phosphodiester
4) 5’
5) 3’
A nucleic acid chain of any length has a __1__ at the start and terminates with a __2__. By convention, the base sequence of a DNA chain is written in the __3__ to __4__ direction.
1) 5’ phosphate
2) 3’ OH
3) 5’
4) 3’
How would you write the complement to this DNA strand?
5’-AGTCT-3’
5’-AGACT-3’
Although it would be oriented TCAGA, you always write it from 5’ to 3’
What is a nucleosome?
DNA wrapped around 8 histone molecules - the basic unit of compacted DNA.
Contains high amounts of arginine and lysine (+ve charge) to bind DNA backbone (-ve charge).
Roughly 146bp of ‘core DNA’ wraps around the histone core, and 60-80bp of ‘linker DNA’ leads to adjacent nucleosome.
How many molecules of DNA make up a chromosome?
2 - each chromatid is made up of one identical strand of DNA
What are the p and q arms of a chromosome?
The binding of the chromatids at the centromere results in four ‘arms’. There are 2 short p arms and 2 long q arms.
What are ‘chromosome territories’?
Regions in the nucleus in which specific chromosomes are localised.
Chromosomes don’t just mix within the nucleus, they are organised into these territories.
DNA replication occurs in the __1__ phase of interphase during the cell cycle. Replication follows several steps that involve multiple proteins called __2__ enzymes and __3__.
DNA replication is vital for cell growth, repair, and reproduction.
1) S
2) replication
3) RNA
Step 1 of DNA replication is __?__.
Replication Fork Formation
Double stranded DNA is ‘unzipped’ into 2 single strands. Base pairs broken by DNA helicase.
Strands form a Y shaped replication fork, which is the template for replication to begin.
Proteins bind to stabilise unwound strands of DNA.
A DNA replication fork has 2 strands in opposing directions. The 3’ to 5’ strand is used to form the __1__ strand, while the 5’-3’ strand is is used to form the __2__ strand.
1) leading
2) lagging
The 3’ to 5’ arm of a DNA replication fork produces a [(1) continuous/ discontinuous] strand of complementary DNA in the [(2) 3’ to 5’/5’ to 3’] direction. This is the __3__ strand.
(1) continuous
(2) 5’ to 3’
(3) leading
The 5’ to 3’ arm of a DNA replication fork produces a [(1) continuous/ discontinuous] strand of complementary DNA in the [(2) 3’ to 5’/5’ to 3’] direction. This is the __3__ strand.
(1) discontinuous (Okazaki fragments)
(2) 3’ to 5’
(3) lagging
Which DNA Polymerase produces Okazaki fragments?
DNA Polymerase-delta
the delta symbol is the lowercase form and looks like an ‘s’
__1__ forms the first 20 base pairs of the leading strand during DNA replication. After that, __2__ takes over. Both enzymes have proofreading 3’ to 5’ exonuclease activity.
1) DNA polymerase-alpha
2) DNA polymerase-epsilon
What is the main physical difference between the leading and lagging strand prior to termination?
The leading strand is continuous and oriented 3’ to 5’; the lagging strand is discontinuous and oriented 5’ to 3’.
Step four (termination) of DNA replication applies to both strands equally. __1__ are degraded and filled by action of __2__ and __3__.
__4__ joins any breaks in the leading and lagging strands to generate continuous double stranded DNA.
1) RNA primers
2) RNAase-H
3) DNA polymerase-delta
4) DNA ligase
True or false: there is only ever one origin of DNA replication on any one DNA strand.
False. It would take far too long, and we know the who genome within a cell replicates in 8 hours.
There are multiple origins of replication with replication forks proceeding in opposite directions (replication bubbles).
What is epigenetics?
Heritable changes to DNA that do not include a change in the DNA sequence.
i.e. changes to gene expression (which genes are switched on and off) which can be passed on to descendants.
What are some examples of epigenetic changes?
HISTONE MODIFICATIONS:
acetylation of Lys, methylation of Lys and Arg
DNA MODIFICATIONS:
Methylation of cytosine
