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Semester 1 - MCBG > 8. DNA structure and replication > Flashcards

8. DNA structure and replication Flashcards

1
Q

What is DNA wound around ?

A

DNA is wound twice around a histone core

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2
Q

Why is it necessary that the DNA is wound around his tones?

A

Important as it allows the DNA to fit in the nucleus and can help regulate transcription

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3
Q

What is the whole structure of dDNA around one histone protein called?

A

Nucleosome

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4
Q

What is the first structure of DNA packaging called?

A

Beads on a string

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5
Q

What is the second structure of packaging called?

A

Solenoid

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6
Q

What is euchromatin?

A

Euchromatin is beads on a string - where gene expression takes place because DNA is more accessible as it not as tightly packaged

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7
Q

What is heterochromatin?

A

Heterochromatin is the solenoid - DNA that is not transcribed because it is tightly wound and packaged so not accessible for transcription factors.

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8
Q

What causes the change from euchromatin(active chromatin) to heterochromatin(inactive chromatin)?

A

DNA methylation

Histone deacetylation

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9
Q

What causes the change from heterochromatin (inactive chromatin) to euchromatin(active chromatin)?

A

DNA demethylation

Histone acetylation

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10
Q

What do chromosomes consist of?

A

Chromosomes consist of many solenoids wrapped tightly around - meaning that genes are not expressed in a chromosome as the DNA is so tightly packed that it is not accessible for transition and translation

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11
Q

What are genes?

A
  • Genes are section of DNA that carry the code for proteins

* Genes have a fixed chromosomal location

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12
Q

What is the genome?

A

• Genome is the entire DNA sequence

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13
Q

How many chromosomes in the human genome?

A
  • Human Genome is 24 chromosomes

* (22 plus 2 sex chromosomes X and Y)

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14
Q

What is the difference between nucleoside and nucleotide?

A

Base + sugar = nucleoside

Base + sugar + phosphate = nucleotide

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15
Q

What are the two peso f pentose sugars?

A

Ribose and 2-deoxyribose

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16
Q

What is the difference between Ribose and 2-deoxyribose ?

A

In ribose, there is an OH group on carbon 2 whereas in deoxyribose, there is a H on carbon 2

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17
Q

What are the two types of nitrogenous bases?

A

Purines and pyrimidines

18
Q

What is the difference between purines and pyrimidines?

A

Purines have 2 rings

Pyrimidines have 1 ring

19
Q

What are the two main types of purines?

A

Adenine and guanine

20
Q

What are the 3 types of main pyrimidines?

A

Cytosine
Uracil
Thymine

21
Q

What are the two types of nucleotides?

A

Ribonucleotide and deoxyribonucleotide

22
Q

In RNA , what is adenine, guanine, uraciland cytosine called as a nucleoside and as a nucleotide?

A

Base - adenine, guanine, uracil, cytosine
Nucleoside - adenosine, guanosine, uridine, cytidine
Nucleotide - adenosine monophosphate, guanosine monophosphate, uridine monophosphate, cytidine monophosphate

23
Q

In DNA , what is adenine, guanine, uraciland cytosine called as a nucleoside and as a nucleotide?

A

Base - adenine, guanine, thymine, cytosine
Nucleoside - deoxyadenosine, deoxyguanosine, deoxythymidine, deoxycytidine
Nucleotide - deoxyadenosine monophosphate(dAMP), deoxyguanosine monophosphate(dGMP), deoxythymidine monophosphate, deoxycytidine monophosphate

24
Q

What are nucleotide joined via?

A

Phosphodiester bonds

25
Q

What is the polarity of the DNA chain?

A

5’ to 3’

26
Q

What are the two distinct chain ends in DNA and RNA?

A

5’ P and 3’OH

27
Q

By convention which direction is the top strand?

A

By convention top strand 5’ to 3’ from left to right !

28
Q

What are the base pairings and how many hydrogen bonds between each?

A

> Only G-C and A-T or A-U base pairing
G-C basepair has 3 hydrogen bonds
A-T basepair has 2 hydrogen bonds > A-U basepair has 2 hydrogen bonds

29
Q

What Rae the two features of DNA strands?

A

DNA strands are complimentary and anti-parallel

30
Q

What is the normal form of the double helix?

A

The normal form of the double helix is the b form which is the right handed double helix

31
Q

Describe what happens at each stage of the cell cycle

A

> G1 - Cell content replication
S phase - DNA replication
G2 - double cheek and repair
M - mitosis

32
Q

What is the best model for DNA replication?

A

the semi-conservative method

33
Q

What I the semi-conservative method for DNA replication?

A
  • where the two strand separate and each strand acts as a template.
  • Each DNA helix produced has one new strand and one old strand.
  • DNA polymerase catalyses reaction to join nucleotides together forming phosphodiester bonds
  • reaction driven by pyrophosphate hydrolysis
  • chain growth is directional, from 5’ to 3’
34
Q

What are the 2 stages of DNA replication in prokaryotes and eukaryotes?

A

Initiation
Elongation
Termination

35
Q

What happens during initiation of DNA replication

A

• Recognition of origin of replication
• DNA helix unzips - hydrogen bonds between base pairs broken by DNA helicase so strands separate
• Requires recruitment of DNA polymerase plus other specific proteins
• Requires a ‘kick-start’ by primase which adds a few of the nucleotides for the new strand
(as DNA polymerase can only extend a 3’end)

36
Q

What direction is DNA made in?

A

5’ to 3’

37
Q

Which direction is DNA read in?

A

3’ to 5’

38
Q

What happens during elongation of DNA replication?

A 
• Moving replication forks
 • Helicase unwinds double helix 
• DNA polymerase extends 3’ ends only
leading to leading strand (continuous), lagging strand (discontinuous) and Okazaki fragments
• DNA ligase joins fragments
39
Q

What happens during termination of DNA replication?

A

when two facing replication forks meet and DNA ligase joins final fragments

40
Q

Why does the lagging strand form?

A

The lagging strand arises due to the fact that the DNA helicase opens up the DNA bit by bit. This means that the DNA polymerase on the template strand goes from 3’ to 5’ so can make the leading strand continuously form 5’ to 3’. However on the strand that goes from template strand 5’ to 3’, the DNA polymerase will need to move back every time more of the helix opens to ensure that it reads from 3’ to 5’

41
Q

What is the difference between prokaryote DNA replication and eukaryote DBNA replication?

A

In prokaryotes, the DNA is circular so there is only one origin of replication and the replication fork will go round the circle.
In eukaryotes, there are many origins of replication and the replication fork will find each other and Joplin by DNA ligase

42
Q

Before replication and after replication, how many DNA molecules in a chromosome?

A

Before replication - one chromosome = one DNA molecule

After replication - one chromosome = two DNA molecule

Semester 1 - MCBG (18 decks)

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