DNA

Question 1

What does DNA stand for?

Answer 1

deoxyribonucleic acid

Question 2

Where is DNA found and what is it?

can be found in 3 places

Answer 2

The nucleus. One copy in two volumes, one from mother and one from father. Used in DNA profiling. High discrimination between individuals. Also found in mitochondria, smaller, circular, multiple copies, less susceptible to degradation, lower discriminatory power. Also found in chloroplasts.

Question 3

What are the base pairs in DNA and are they purines or pyrimidines?

Answer 3

Guanine = purine
Cytosine = pyrimidine
Adenine = purine
Thymine = pryrimidine

Question 4

What are the base pairings in DNA and RNA?

Answer 4

DNA:
Adenine + Thymine
Guanine + Cytosine
RNA: 
Adenine + Uracil 
Guanine + Cytosine

Question 5

What is the basic structure of DNA?

Answer 5

double helix
antiparallel strands in 5’ to 3’ direction
sugar-phosphate backbone

Question 6

What does a nucleotide consist of?

Answer 6

five carbon sugar
nitrogenous base
phosphate

Question 7

How many hydrogen bonds are between the bases?

Answer 7

A + T = 2 H bonds

G + C = 3 H bonds

Question 8

What is the total length of DNA in haploid?

Answer 8

3x10^9 base pairs

Question 9

What is the distance from one base pair to the next?

Answer 9

0.34nm

Question 10

Chromosomes

Answer 10

genome divided up into chains and packaged separately as chromosomes.
23 pairs (22 autosome pairs, 1 pair of sex cells)
two chromatids
held together by a centromere
short ‘p’ arm
long ‘q’ arm
telomere at end of each chromatid
proteins e.g histones important in packaging the DNA so it can form a chromosome.

Question 11

What percent of DNA is coding?

Answer 11

2%

Question 12

Repetitive DNA

Answer 12

Tandemly repeated DNA is very important as is what’s used for DNA fingerprinting and profiling.
satellites
minisatellites or VNTR’S = not used much
microsatellites or STR’s = current basis of DNA profiling

Question 13

Homozygous and Heterozygous

Answer 13

at each STR locus, there are two alleles
homozygous = both alleles same e.g. AGAT repeated 8 times, AGAT repeated 8 times, reported as 8,8 genome
heterozygous = alleles different e.g. AGAT repeated 8 times, AGAT repeated 5 times, reported as 5,8 genotype.

Question 14

Where can STR’s be found?

Answer 14

within genes (both coding and non-coding parts) and between genes.
in genome, there are often large stretches of DNA between genes.

Question 15

Example gene

Answer 15

Promoter, 1, intron, 2, intron, 3 , intron, 4, intron, 5

Question 16

What is the promoter?

Answer 16

control region, transcription factors and RNA polymerase binds to DNA double helix

Question 17

What is the 1-5 in the example gene?

Answer 17

exons

Question 18

Are exons coding or non-coding?

Answer 18

coding

Question 19

Are introns coding or non-coding?

Answer 19

non-coding

Question 20

Transcription

Answer 20

• proteins (TBP) bind to a region of the promoter called the TATA box.
• RNA polymerase binds to complex of proteins
• two strands of DNA are separated
• RNA polymerase proceeds to read one strand, it polymerises ribonucleotides into a strand of RNA called the primary transcript of pre-mRNA.
• the primary transcript is an RNA copy that includes both exonic and intronic sequences
• this primary transcript has to be modified to produce mature messenger RNA that can be translated.

Question 21

RNA processing - capping

Answer 21

add 7-methylguanylate to the 5’ end. Cap helps to prevent breakdown of mRNA by nucleases and is vital for ribosome assembly on the mRNA and therefore translation. The cap also aids the exit of mRNA from the nucleus.

Question 22

RNA processing - Polyadenylation

Answer 22

add a poly-A tail to 3’ end. About 200 ‘A’ residues are added to the 3’ end by polyA polymerase after the 3’ end of the DNA is shortened by cleaving it shortly after the polyA signal. The polyA tail helps to prevent breakdown of the mRNA by nucleases.

Question 23

RNA processing - Splicing

Answer 23

remove introns and join exons. This gives mature mRNA that can be exported from the nucleus and translated into proteins.

Question 24

Translation

Answer 24

translation start = AUG/methionine
translation stop = one of three stop codons
-areas at end are called untranslated regions
-code read in groups of 3