DNA function, structure and replication

Question 1

What are the functions of DNA? (3)

Answer 1

1. Storing and transferring genetic information
2. Template and regulator for transcription and protein synthesis.
3. DNA is the genetic material thus the structural basic of hereditary and genetic diseases.

Question 2

Where is DNA found?

Answer 2

In the nucleus and mitochondria

Question 3

How is DNA arranged?

Answer 3

• Arranged in a double helix with complimentary base pairing
• DNA coils around proteins (histones) and form nucleosomes > supercoils > chromosomes

Question 4

How many chromosomes are there?

Answer 4

46, 22 pairs and a pair of sex chromosomes (X,Y)

Question 5

What is a Karyotype?

Answer 5

number and appearance of chromosomes in a cell. Spreads are arranged in size order

Question 6

Prokaryotes and DNA?

Answer 6

No nuclear membrane, DNA arranged in a single chromsome

Question 7

Eukaryote and DNA?

Answer 7

• DNA is in a nucleus, bound to proteins (chromatin complex)
• Each chromosome is made of 2 identical strands of chromatids joined in the centre (centromere).
• Some DNA is found in mitochondria (purely maternal DNA.)

Question 8

What is the structure of a nucleotide base?

Answer 8

• Phosphate group (energy for reactions)
• Sugar group
• Nitrogenous base

Question 9

What is a duplication mutation?

Answer 9

sections repeating leading to an incorrect protein generated

Question 10

What is a deletion mutation?

Answer 10

Out of frame – sequence shifts meaning the reading frame of the gene is changed.

In frame – whereby one codon is removed thus only one amino acid is lost. Reading frame is not changed.

Question 11

What does a mutation of regulatory sequence mean?

Answer 11

coding sequence still intact, but gene itself is switched on or off etc

Question 12

How can DNA be damaged?

Answer 12

From chemicals, UV and radiation

Question 13

How can DNA have issues with repairing?

Answer 13

base or nucleotide excision, mismatch repair or transcription-couples repair

Question 14

What is a Non-Sense mutation?

Answer 14

Point mutation that produces a stop codon - results in an incomplete, usually non-functional protein. E.g. Duchenne’s muscular dystrophy

Question 15

What is a Mis-Sense mutation?

Answer 15

A point mutation in which a single nucleotide change results in a codon that codes for a different amino acid (substitution). This can have a varied affect and can result in a silent mutation and a non functional protein E.g Sickle cell disease where CAG was replaced with CTG.

Question 16

What is a spice site mutation?

Answer 16

Affects the accurate removal of an intron

Question 17

what is an expansion of tri-nucleotide repeat?

Answer 17

Huntington’s disease : CAG. Triple repeat is repeated several times in the first part of the coding sequence If > 36, the patient will develop Huntington’s-

Question 18

What is meant by the process anticipation?

Answer 18

In diseases such as Huntington’s, repeats get bigger when they are transmitted to the next generation resulting in earlier symptoms of greater severity t his process is called anticipation.

Question 19

What is meant by heterogeneity?

Answer 19

One gene one variant one disease e.g. Huntingtons

ALLELIC HETEROGENEITY - Lots of different variants in one gene e.g. cystic fibrosis
LOCUS HETEROGENEITY - Variants in different genes give the same clinical condition e.g. hypertrophic cardiomyopathy
Different variants in the same gene can give rise to different clinical conditions – genotype/phenotype correlations