Foundation Block Molecular Biology

Question 1

Define Gene

Answer 1

Basic functional unit of heredity. Specific DNA nucleotide sequence that acts as instructions to make functional molecules including proteins and various types of RNAs

Question 2

Define allele

Answer 2

Most genes are the same in all people but a small number of genes are slightly different. Alleles are forms of the same genes with differences in their DNA bases. Those differences can be disease-causing (pathogenic), can lead to difference in physical features or have no effect (benign)

Question 3

True or false: All genes encode proteins

Answer 3

False - Not all genes encode proteins

Question 4

Define Heterozygous

Answer 4

Two alleles of a gene are different from each other e.g. wild-type and mutated

Question 5

Define homozygous

Answer 5

Both the alleles are identical

Question 6

Define autosome

Answer 6

Non-sex chromosome

Question 7

What is the approximate percentage of DNA that is identical from person to person

Answer 7

99.9% identical (99.95% in coding regions)

Question 8

How many genes do we have in DNA and how many are active?

Answer 8

20000 genes
10000 are active in any one cell type

Question 9

What is the first step for synthesis of a protein?

Answer 9

Unpackaging the chromosome/250nm wide loop into strands of DNA. Then transcription and translation occurs

Question 10

Describe the process of transcription

Answer 10

The DNA is unwinded/’unzipped’/broken apart
Allows access for the bases that make up the RNA (ATP, GTP, CTP and UTP) to join the template strand via complementary base pairing
RNA polymerase joins the RNA nucleotides together via condensation reactions in a 5’ to 3’ direction
The RNA complex moves from left to right, unwinding, copying and rewinding as well as generating RNA as it goes along
DNA template strand is complementary and antiparallel to the coding strand
The produced RNA is identical to the coding strand (except Thymine which is replaced by Uracil)

Question 11

How can one gene make many different proteins?

Answer 11

Exons can be combined in different ways to generate multiple different options - “splice isoforms”
Alternative splicing is a regulated event; different isoforms or different ratios are produced in different cells/tissues/ or at different times

Question 12

What types of gene regulation are there?

Answer 12

Epigenetic Regulation
Transcriptional Regulation
Transcript Processing and Stability Regulation
Translation Regulation
Post Translational Regulation

Question 13

What type of epigenetic regulations are there?

Answer 13

DNA Methylation, Histone Acetylation and Protein Ubiquitylation

Question 14

What type of Transcriptional Regulations are there?

Answer 14

Transcription Factors, Enhancers and Repressors and Steroid Hormones

Question 15

What type of Transcript Processing and Stability Regulation are there?

Answer 15

Alternative Splicing, microRNA - mediated Degradation, Non-sense mediated degradation and Capping/polyA/RNA binding proteins

Question 16

What type of translation regulation are there?

Answer 16

Micro RNA and long-noncoding RNAs

Question 17

What type of Post Translational Regulation are there?

Answer 17

Phosphorylation (kinases/phosphatases), Glycosylation, Ubiquitylation/De-ubiquitylation

Question 18

How can you determine the amount of protein produced within a cell or tissue (gene product)?

Answer 18

Is the net difference between production and degradation
Production - degradation

Question 19

Define Dominant Mutation

Answer 19

Mutations that activates an (abbrant) function or alters a structure or in proteins that are very sensitive to abundance are likely to have a dominant effect. For example, prevents normal protein function or inhibits normal polymer assembly

Question 20

Define Recessive Mutations

Answer 20

Mutations that lead to a loss of function are likely to be recessive.

Question 21

Is Huntington’s disease dominant or recessive?

Answer 21

Dominant mutation

Question 22

Describe what happens in someone to cause Huntington’s disease?

Answer 22

In a normal individual we have somewhere under 35 (about 27) repeats of CAG motif within the Huntington protein. This encodes for a glutamate. With the Huntington Mutation, we have a rapid extension of CAG repeats to 100 or 200 repeats so more glutamate proteins produced. The more repeats means more neurodegeneration of parts of the brain known as the basal ganglia. The problem is that the protein acts as a poison for the neurone by aggregating and leading to oxidative stress leading to apoptosis

Question 23

What is Aniridia?

Answer 23

One functional copy of PAX6 gene and one non-functional copy of PAX6 gene.
Produces 50% of PAX6 protein
PAX6 is a transcription factor, it controls expression of many other genes. It’s function is dose dependent… too little expression and it doesn’t activate all the genes it needs to.
We refer to these conditions as “haploinsufficient”

Question 24

What is Cystic Fibrosis?

Answer 24

Caused by an autosomal recessive mutation in the Cystic Fibrosis Receptor (CFTR) which acts as an ion channel that allows chloride ions to move out.
Mutant form does not work as an ion channel.
However, in heterozygous individuals with one functioning ion channel, there are still enough areas where the ion channel works.

Question 25

What type of mutation is Sickle Cell Anaemia?

Answer 25

Recessive Mutation

Question 26

What is Sickle Cell Anaemia?

Answer 26

Caused by a mutation in normal beta-globin of CTC to CAC changing the protein coded for from Glu to Val. Every haemoglobin molecule is actually a tetramer of four parts, alpha, beta, alpha and beta and this mutation results in a change in a beta chain as a negative charge is lost.
Leads to concave, sickle-shaped red blood cells that end up clotting and blocking blood flow.