1. Mol. med

Question 1

Describe how the information on DNA is used during transcription to construct polypeptides, including the role of mRNA, tRNA and the ribosomes

Answer 1

Transcription, occurring in the nucleus –
1. DNA molecule unwinds (topoisomerase unwinds the supercoil)
2. DNA strands separate (helicase – breaks H bonds)
3. Transcription factors
4. RNA mononucleotides line up against their complementary bases
primase
5. H-Bonds form between the complementary bases (RNA polymerase – works 5 prime to 3 prime end to only help align the mononucleotides) – AU 2 bonds, CG 3 bonds
RNA primase-helps it work backwards (lagging strand 3–>5)
6. Phosphodiester bonds form between adjacent RNA mononucleotides (RNA ligase)
7. mRNA molecule is formed
8. Leaves cell nucleus to enter cytoplasm and bind to a ribosome

Question 2

Define a single nucleotide polymorphism (SNP)

Answer 2

One base is changed in a sequence, but doesn’t lead to a change in amino acids so it’s not a pathogenic mutation (could be due to degenerate nature of genetic code)

Question 3

Describe how a single nucleotide alteration in DNA can result in structural and
functional change in its protein product, using haemoglobin S in sickle cell anaemia as an example

Answer 3

Single base is changed, but forms a pathogenic mutation as it results in a whole amino acid being changed (in sickle cell = valine to glutamine). Primary structure of the protein will be different due to a different amino acid sequence. This is an example of a mis-sense mutation.
This changes the shape of the tertiary and quaternary structure of the protein due to the positional changes of the bonds, meaning it will not function in the same way.
In sickle cell, it makes deoxyhaemoglobin less soluble, which makes the red blood cells more likely to adhere to the endothelium of blood vessels. Hb-S polymerises at low oxygen concentrations = makes the molecule longer and more likely to adhere to endothelial cells.
In sickle cell crisis – the larger/polymerised molecule causes endothelial damage which triggers an inflammatory response. The ischemic pain is caused by blockage of capillaries, reducing blood flow to the area. Triggered by alcohol, exercise, stress, smoking etc. this disease is more common in African-Caribbean people and in the heterozygous it’s protective against malaria. It’s an autosomal recessive condition, and hasn’t died out due to the protective effect it has against malaria.
Treated with hydroxycarbamide (hydroxyurea) – causes the gene expression of foetal haemoglobin instead to try and compensate for the low haemoglobin concentration they have.
Foetal haemoglobin = 2 gamma and 2 alpha chains rather than 2 beta and 2 alpha chains in adult haemoglobin.
Another symptom of sickle cell anaemia is jaundice due to increased haemolytic rate. This would be a type of pre-hepatic jaundice, so the blood level of unconjugated bilirubin will be high.

Question 4

Describe how the information on DNA is used during translation to
construct polypeptides, including the role of mRNA, tRNA and the ribosomes

Answer 4

Translation, occurring in cytoplasm -

1. mRNA binds to a ribosome (binding site on RNA) – rough endo reticulum?
2. tRNA anticodons bind to codons on mRNA
3. 2 tRNA molecules can be present in a ribosome at any one time
4. tRNA carry amino acids
5. Adjacent amino acids join together by peptide bonds to form a polypeptide chain
6. This then sent to smooth endoplasmic reticulum for modifying
7. Peptidyle transferase catalyses the formation of peptide bonds
8. Stop codon UAA, UAG, UGA

Question 5

Foetal and adult haemoglobin

Answer 5

Foetal haemoglobin = 2 gamma and 2 alpha chains rather than 2 beta and 2 alpha chains in adult haemoglobin.

Question 6

primary
secondary
tertiary
quaternary

Answer 6

sequence
sheets and spirals
R group bonds (hydrophillic)
multiple proteins

Question 7

RNA splicing

Answer 7

snurps + spliceosome

exons (kept bits) + introns

Question 8

start codon

stop codon

Answer 8

AUG

UAA, UGA, UAG

Question 9

DNA vs RNA

Answer 9

DNA= double stranded with compl. chain
RNA=single stranded, any double stranded is wiht itself. mRNA, rRNA, tRNA
DNA is present at all times many mRNA accumulate following cell stimulation

Question 10

mRNA

Answer 10

messenger

Question 11

tRNA

Answer 11

translating

Question 12

rRNA

Answer 12

ribo. binding site,

Question 13

DNA

Answer 13

deoxyribnucleic acid
per chromosome (tend to be in pairs)
polynucleotides
adenin-thyanin
cytosine-gluanine
uracil
double helix
sulphar phosphate bonds

Question 14

F. A gene sequence is coded in

Answer 14

Single strand DNA

Question 15

F. A promoter sequence is coded in

Answer 15

Single strand DNA

Question 16

F. Specific amino acids bind to

Answer 16

Transfer RNA

Question 17

F. The transcriptome is composed of

Answer 17

Messenger RNA

Question 18

F. Alternative splicing producing different gene products occurs in

Answer 18

Messenger RNA.

Question 19

F. A protein with two peptide chains held together by cross-links has this structure

Answer 19

Quaternary structure

Question 20

F. Cis/trans and L/D isomers are proteins that differ in

Answer 20

Tertiary stricture

Question 21

F. Alpha helixes and beta sheets are examples of protein

Answer 21

Secondary structure

Question 22

F. Sickle cell anaemia (HbS) is caused by

Answer 22

An autosomal recessive inherited condition substituting an amino acid in the beta globin chain

Question 23

F. In hypoxia, the abnormal HbS

Answer 23

Crystallises (insoluble

Question 24

F. The Hb structural change causes sickling by

Answer 24

Binding to the cytoskeleton

Question 25

F. The sickle cells cause capillary occlusion by

Answer 25

Binding to and activating endothelial cells causing inflammation

Question 26

F. An acute pain crisis is typically caused by capillary occlusion in the

Answer 26

Bone (most common presentation).

Question 27

F. Sickle cell disease can be treated with hydroxyurea because it

Answer 27

Increases synthesis of HbF (fetal Hb). HbF does not have an abnormal beta chain