Intro to DNA 1 Flashcards Preview

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Flashcards in Intro to DNA 1 Deck (27)
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1
Q

What chromosomes do normal humans have?

A

22 pairs of autosomes and 1 pair of allosomes

2
Q

What is heterochromatin?

A

DNA that is tightly packaged around the histone, so the genes are not expressed

3
Q

What is euchromatin?

A

Beads on a string model of DNA, so genes are expressed as the DNA is loosely packaged

4
Q

What is a nucleosome?

A

A section of DNA wrapped twice around a histone core

5
Q

What is the DNA between histones called?

A

Linker DNA

6
Q

How many proteins make up a histone?

A

8 (so it’s an octamer)

7
Q

What is a solenoid?

A

A section of heterochromatin

8
Q

Are genes expressed in chromosomes?

A

No

9
Q

What’s the difference between nucleotides and nucleosides?

A

Nucleotides are a base + sugar + phosphate, whereas a nucleoside is only a base + sugar

10
Q

What’s the difference between ribose and n-deoxyribose? What is n?

A

n=2, as the second carbon in ribose has an OH attached whereas in 2-deoxyribose it has a H

11
Q

What’s the difference between purines and pyrimidines?

A

Purines have two rings (adenine, guanine) (nucleoside ends in -sine) whereas pyrimidines have just one (cytosine, uracil, thymine) (nucleoside ends with -dine)

12
Q

Which nitrogenous bases are zwitterions?

A

Cytosine and guanine

13
Q

How are nucleotides joined?

A

Phosphodiester bonds between C5 and C3 of the pentose sugar

14
Q

Which way is the DNA chain usually written?

A

5’ (prime) to 3’

Only the top strand which runs 5’ to 3’ is written by convention

15
Q

What is at each end of a DNA chain?

A

At 5’ end - phosphate group

At 3’ end - OH group

16
Q

What is the name given to the way a DNA double helix twists?

A

Right handed helix

17
Q

How does the secondary structure of DNA affect gene expression?

A

In the major groove (bigger gap) genes are expressed, in the minor groove they aren’t

18
Q

Describe the cell cycle

A

1) Mitosis - cell division
2) G1 - cell content replication
3) S - DNA replication
4) G2 - double check and repair

19
Q

How does DNA polymerase catalyse the start of DNA replication?

A

It separates DNA strands (dNMP)n and catalyses the reaction of adding a deoxynucleoside triphosphate (dNTP) to the 3’ end of a DNA strand, extending the chain ((dNMP)n+1 and releasing a pyrophosphate (PPi) which is then hydrolysed by DNA polymerase to break it down into inorganic phosphate to release energy

20
Q

How did they first discover DNA replication?

A

Through circular DNA in prokaryotes

21
Q

What are the three steps of DNA replication in prokaryotes?

A

Initiation, elongation, termination

22
Q

What is initiation in terms of DNA replication in prokaryotes? What does it require?

A

Recognition of origin of replication
Requires recruitment of DNA polymerase plus other specific proteins
Requires a ‘kick-start’ by primase (as DNA polymerase can only extend a 3’ end)

23
Q

Which way does DNA polymerase read DNA?

A

3’ to 5’, as it has to add a dNTP on the 3’ end

24
Q

What breaks the bonds between base pairs, and what are those bonds called?

A

DNA Helicase

Hydrogen bonds

25
Q

What are the two strands which are formed from the antisense strand called during DNA replication?

A

Lagging strand and Leading strand (continuous)

26
Q

What are sections of replicated DNA strands called?

A

Okazaki fragments

27
Q

What joins Okazaki fragments?

A

DNA Ligase