2.1, 2.2 Introduction To DNA and precision med

Question 1

What is a DNA molecule and its function? (3)

Answer 1

1. Deoxyribonucleic acid
2. Double helix
3. Contains genes - Length of DNA that codes for a protein

Question 2

How is DNA packaged to form a chromosome?

Answer 2

1. DNA wrapped around a histone forming ‘beads on a string’
2. Further compressed into a solenoid
3. Further folds to form our chromosome

Question 3

What is a piece of DNA wrapped around a singular histone called?

Answer 3

A nucleosome

Question 4

What is chromatin?

Answer 4

DNA + histone proteins

Question 5

Describe the structure, function and colour on microscopy of heterochromatin (2)

Answer 5

1. Solenoid form of DNA and histones
2. Genes are not expressed
3. Darker

Question 6

Describe the structure, function and colour on microscopy of euchromatin (2)

Answer 6

1. Beads on a string
2. Genes are expressed
3. Lighter

Question 7

What are genes?

Answer 7

1. Distinct sequence of nucleotides that carry a code for proteins

Question 8

What is the human genome?

Answer 8

Entire DNA sequence in humans i.e. Humans - 23 pairs of chromosomes

Question 9

What are autosomes and how many do we have? (2)

Answer 9

1. Chromosomes that contain genes that relate to anything but sex determination
2. We have 22 autosomal pairs (i.e. 44) and 1 pair of sex chromosomes (i.e 2)

Question 10

Name and describe the structure of the two pentose sugars that can be found within our bodies. Where are these located?

Answer 10

1. Ribose - pentose sugar with OH group on 2nd Carbon within ring - located in RNA
2. Deoxyribose - pentose sugar with H group on 2nd carbon within ring - located in DNA

Question 11

What is the difference between a nucleotide and nucleoside?

Answer 11

Nucleotide - phosphate + sugar + base

Nucleoside - sugar + base

Question 12

What are the two types of nitrogenous bases, name the base pairs that associate with them and how many rings each base has.

Answer 12

1. Purines - Adenine, Guanine - 2 rings

2. Pyramidines - Thymine, Cytosine, Uracil - 1 ring

Question 13

How many hydrogen bonds do the base pairs A and T and G and C make?

Answer 13

A and T - 2

G and C - 3

Question 14

Describe the two DNA strands that bond together forming our DNA molecule.

Answer 14

1. DNA strands are COMPLEMENTARY
2. run ANTI-PARALLEL to each other
3. By convention, top strand always written 5’ to 3’

Question 15

What bonds join nucleotides to each other forming the DNA strands? What parts of the nucleotide make this bond? (2)

Answer 15

1. Phosphodiester bonds
2. 3’ Carbon to the oxygen to the Phosphate
3. Distinct ends, 5’ Phosohate and 3’ OH

Question 16

Where does DNA replication occur within a cycle of mitosis?

Answer 16

Within the S phase

Question 17

What is the term describing the DNA replication process and the fact that each new molecules has 1 recycled strand?

Answer 17

Semi-conservative

Question 18

Describe the DNA replication process in eukaryotes

Answer 18

1. Initiation
   - DNA helicase unwinds DNA at origin of rep
   - single strand binding proteins keep strand separated
   - DNA primase kick starts addition of nucleotides by adding short sequences of RNA called primers
2. Elongation
   - leading strand - DNA polymerase takes over and elongates
   - lagging strand - okazaki fragments formed as DNA polymerase works in 5’ to 3’ direction continuously only on 3’ to 5’ strand.

• Exo/endonuclease proof reads replication
• polymerase reverses and corrects
• DNA ligand seals okazaki fragments into one continuous strand

3. Termination
   - two facing replication forks meet and DNA ligase joins final fragments

Question 19

Name a difference in prokaryotic and eukaryotic DNA rep

Answer 19

Eu - many origins of replication

Pro - 1 origin of replication

Question 20

Describe the DNA replication process in prokaryotes

Answer 20

1. Recognition of origin of replication
2. Primase
3. DNA polymerase + other specific proteins

Question 21

What drives the addition of nucleotides onto elongating strand?

Answer 21

Loss of pyrophosphate (PPi)

Question 22

One DNA molecule is called a chromosome, what are the two DNA molecules after replication called?

Answer 22

A chromosome too! Have sister chromatids which are identical.

Question 23

Briefly describe precision medicine

Answer 23

Moving from one-size-fits-all medicine to tailored therapy.

Involves pharmacogenetics - Study of how a persons genes affect their response to a drug

Question 24

What are immunotherapeutic checkpoint inhibitors?

Answer 24

Immune checkpoint inhibitors unleash a patients own T cells to kill tumours (e.g. For cancer)

Question 25

What is DNA ligase?

Answer 25

Joins nucleotides together by catalysing the formation of phosphodiester bonds

Question 26

What are okazaki fragments?

Answer 26

Newly synthesised DNA fragments formed on lagging parent strand during DNA replication

Question 27

What is epigenetics?

Answer 27

Study of changes in organisms caused by modification of gene expression as opposed to alteration to genetic code itself