DNA intro

Question 1

What is the smallest unit in DNA packaging?

Answer 1

A nucleosome
It’s DNA wrapped twice around one histone protein.

The DNA then links these nucleosomes together in a chain (beads on string)

Question 2

What is a solenoid?

Answer 2

All the nucleosomes are linked like beads on a string. This string then could together tightly to form a solenoid (also called a fibre)

Question 3

How are Heterochromatin a and euchromatin packaged differently?

Answer 3

The euchromatin sure like beads on a string it’s exposed and the genes can be expressed.

Heterodox chromatin is solenoid fibres, they are tightly bound so genes are not expressed.

Question 4

In what form are genes when in a chromosome in replication ?

Answer 4

They are tightly packaged solenoids and so the genes are not expressible.

Question 5

What are genes and where are they found?

Answer 5

They contain the coding for proteins and have a chromosomal location.

Question 6

What is a genome?

Answer 6

The genome is the entire DNA sequence.

The human genome is 24 chromosomes (22 autosomes + 2 sex chromosomes)

Question 7

What is the basic structure of DNA?

Answer 7

Bases, protected by a phosphosuagr backbone. Made from nucleotides and helixes
The strand run antiparrelel
Form a double right handed helix

Question 8

What is a nucleotide?

Answer 8

Contains a single base + pentose sugar + phosphate

Question 9

What is a nucleoside?

Answer 9

Base + pentose sugar (no phosphate)

Question 10

What the difference between RNA and DNA?

Answer 10

The pentose sugar.

On RNA its ribose, on DNA it loses a H from the 2nd carbon to become 2-deoxyribose.

Question 11

What is a purine?

Answer 11

A two ring base = adenine and guanine

Question 12

What is a pyrimidine?

Answer 12

A one ring base. = thymine and cytosine and uracil

Question 13

What is distinct about a DNA chain?

Answer 13

It has polarity 3” to 5”

The 3” is the OH end and the 5” is the P end.

Question 14

How are bases paired?

Answer 14

Hydrogen bonds.
2 between T/U and A
3 between C and G

Question 15

How is a DNA sequence written?

Answer 15

Conventionally it runs left to right 5” to 3”

Question 16

What is the accepted model for DNA replication?

Answer 16

The semi-conservative model

Question 17

What are the main points of DNA replication?

Answer 17

Catalysed by DNA polymerase 
Strands are separated 
It’s a stepwise reaction 1 base at time 
Reaction dire by pyrophosphate hydrolyses 
Chain grows from 5” to 3”

Question 18

What are the 3 steps of DNA replication in prokaryotes?

Answer 18

Initiation
Elongation
Termination

(Of a circular naked chromosome)

Question 19

What happens in the initiation step of prokaryotic DNA replication?

Answer 19

A replication fork forms and DNA polymerase joins the 3” end of the strand so it begins making 5” to 3”.

Question 20

What happens in the elongation step of prokaryotic DNA replication?

Answer 20

The DNA polymerase runs along the DNA from 3” towards 5” creating a new strand for each template strand.

DNA ligase puts together the Osaka fragments that are formed in the lagging strand .

DNA helicase continues to unwind the double helix.

Question 21

What happens in the termination stage of prokaryotic DNA replication?

Answer 21

The lagging strand and leading strand meet and are linked by DNA ligase, to form one strand.