1 - Intro To DNA

Question 1

What is the structure of DNA?

Answer 1

• Right handed double helix
• Antiparallel complementary strands held together by hydrogen bonds between complementary base pairs
• 2-deoxyribose
• Phosphodiester backbone
• Polar due to 5’ 3’ ends
• Major/minor groove

Question 2

What is chromatin?

Answer 2

DNA wrapped around histones (octomer of proteins) , which can then condense to form chromosomes

Question 3

What is the structure of euchromatin and heterochromatin?

Answer 3

Euchromatin: Light. Beads on a string, when DNA being replicated. Less dense as acetylated.

Heterochromatin: Dark, solenoids packed to form a 30nm fibre. Dense as methylated. Gene not expressed like this

Question 4

What is the name of DNA and a histone together?

Answer 4

Question 5

Where do proteins for DNA replication bind to DNA?

Answer 5

Major groove as easily accessible

Question 6

What is the process of forming a chromosome?

Answer 6

• DNA wraps around histones to form nucleosomes and beads on a string
• Nucleosomes wrap around one another and form solenoids
• Solenoids join together to become fibres
• Fibres zigzag over one another to become highly condensed loops

Question 7

What is the genome?

Answer 7

• Entired DNA sequence
• 24 chromosomes, 2 sex 22 auto

Question 8

What are nucleosides?

Answer 8

• Sugar and base, no phosphate
• Adenosine, Guanosine, Uridine, Deoxythymidine, Cytidine

Question 9

What are the two classifications of nucleotide bases?

Answer 9

• Purines (2 C ring): A,G
• Pyrimidines (1 C ring): T,C,U

Question 10

How would you find a gene on a chromosome if you knew the exact position?

Answer 10

LOOK AT THE BANDING PATTERNS

Question 11

Why can C only bind to G?

Answer 11

• 3 hydrogen bonds
• All bonds of nearly equal distance

Question 12

Why is DNA antiparallel?

Answer 12

Ensure the bases are close together and in the middle so they can form hydrogen bonds

Question 13

What is the nomenclature of DNA?

Answer 13

• Left to right 5’ to 3’
• Complementary is 3’ to 5’

Question 14

What is the cell cycle and where are the checkpoints?

Answer 14

Question 15

What is the equation for DNA replication?

Answer 15

(dNMP)n + dNTP –> PPi + (dNMP)_n+1

Question 16

What does DNA polymerase do?

Answer 16

• Reads in 3’ to 5’ direction
• Elongates in 5’ to 3’ direction
• Catalyses phosphodiester bond using energy from PPi hydrolysis
• Can proof read

Question 17

How is DNA replication started?

Answer 17

• Primase (RNA Polymerase) makes a primer which binds to the start of DNA wanting to be replicated
• DNA polymerase binds to primer to start elongation

Question 18

What is the process of DNA replication?

Answer 18

1. Initiation

• Topoisomerase and DNA helicase unwind the double helix to form replication forks with two template strands (one leading one lagging)
• Primase produces short primers that bind to the 3’ ends of the DNA

2. Elongation

• DNA polymerase binds to primers and reads in 3’ to 5’ direction, adding complementary base pairs to the primer in a 5’ to 3’ direction
• On the lagging strand (5’ TO 3’ orientation) there are lots of primers so okazaki fragments are formed and replication is discontinuous

3. Termination

• Replication forks meet
• Primers removed and replaced with appropriate bases
• DNA strand proofread
• DNA ligase joins okazaki fragments
• Semi conservative replication

Question 19

If DNA polymerase works at 100 nucleotides a second, and a DNA molecule is 6000 nucleotides long, how long will replication take?

Answer 19

• Impossible to know as there are so many replication forks running in different directions, not just one DNA polymerase

Question 20

How do prokaryotes and eukaryotes differ?

Answer 20

Prokaryotes have:

• Smaller ribosomes
• Nucleoid (no nucleus)
• Plasmid
• Slime capsule
• Flagella
• Cell wall of muerin
• No membrane bound organelles

Question 21

Why are nucleosides used for analogue drugs instead of nucleotides?

Answer 21

Nucleotides are charged so would be difficult to get them to cross the membrane