Nucleic Acid, Replication, Transcription and mRNA processing Part 3 - (Week 5) Flashcards
1
Q
What is involved in a DNA double helix?
A
- B form of DNA
- 2 polynucleotide chains that run antiparallel
- diameter = 20A
- has major wide groove, + minor narrow groove
2
Q
What is the antiparrellel nature of DNA?
A
- the opposite direction of the 2 strands of nucleotides
3
Q
What are the basics of DNA replication?
A
- base pairing to a template strand
- 2 strands = complementary, each strand acts as a template for building a new strand in replication
- DNA replication, parent molecule unwinds = 2 new daughter strands = built based on base- pairing rules
4
Q
What does Watson & Crick’s semiconservative model of replication predict?
A
- when a double helix replicates, each daughter molecule will have one old strand (derived/conserved) from parent molecule = one newly made strand
5
Q
What is involved in DNA replication?
A
- remarkable speed and accuracy
- replication of DNA = undertaken by a complex of enzymes that separate the parental strands & synthesise the daughter strands
- free nucleotides = produced in cytoplasm + present in the nucleus prior to replication
6
Q
What is denaturation?
A
- involves the separation of the two strands due to breaking of H-bonds between bases
7
Q
What is renaturation?
A
- reassociation of denatured complementary single strands of a DNA double helix
8
Q
What happens at the origins of replication?
A
- where replication begins
- 2 strands = separated, opening a replication bubble
- proceeds in both directions
- eukaryotes have large = long DNA pieces
9
Q
What is theta replication?
A
- used for replication of circular chromosome bacteria
10
Q
Where does linear DNA replication take place?
A
Eukaryotic chromosomes
11
Q
How does DNA replication start?
A
- primase starts an RNA chain, the primer
- attaches to the template = adds RNA nucleotides one at a time with the parental DNA as a template
- primer = short, its 3’ end serves as a starting point for the new DNA strand
- DNA polymerases catalyse the elongation of the new DNA
12
Q
What happens in DNA strand elongation?
A
- each nucleotide that is added to a growing DNA strand = part of a dNTP molecule
dNTP has deoxyribose while rNTP has ribose - each monomer of dNTP joins the DNA strand, it loses 2 phosphate groups as a molecule of pyrophosphate
- new strand = antiparrellel
13
Q
What do we know about DNA elogation?
A
- All DNA polymerases require a 3’ -OH priming end to initiate DNA synthesis = can only DNA from 5’ to 3’ direction
- the leading strand = continuous
14
Q
Replication = semi-discontinuous. True or False?
A
True - leading strand = synthesized continuously
lagging strand = synthesised discontinuously in Okazaki fragments
15
Q
What happens in proofreading and repairing DNA?
A
- DNA polymerases proofread newly made DNA, replacing incorrect nucleotides
- repairs enzymes correct errors in base pairing in mismatch pairing
- can be damaged by exposure to harmful chemicals/physical agents/ cigarettes = X rays, undergo spontaneous changes
- Sequence changes become permanent = can be passed on to the next generation
