Module 1 - DNA Structure

Question 1

Why is DNA important>

Answer 1

Vital for all living things
Hold instructions for an organisms development, survival and reproduction
Long term storage = very stable

Question 2

Role of genes in cell

Answer 2

• Units of biological info
• Units of inheritence

Question 3

Nucelotide Structure

Answer 3

• DNA Polymer made up of nuleotides
• sugar = 2’ deoxyribose
• 3 phospahte groups: furthest from sugar is gamma, middle is beta, closest to sugar is alpha
• base = Adenine, Thymine, Guanine, Cytosine

Question 4

Bases

Answer 4

Purine - 2 rings = A & G
Pyrimadine - 1 ring = T & C
Base attached to sugar via B-N-glycosidic bond

Total number of purines is equal to number of pyrimadines (CHARGAFF’s Rule)

Question 5

Names of 4 nucleotides

Answer 5

2’-deoxyadenosine 5’-triphosphate (dATP)
2’-deoxyguanosine 5’-triphosphate (dGTP)
2’-deoxycytidine 5’-triphosphate (dCTP)
2’-deoxythymidine 5’-triphosphate (dTTP)

Question 6

Names of 4 nucleotides

Answer 6

2’-deoxyadenosine 5’-triphosphate (dATP)
2’-deoxyguanosine 5’-triphosphate (dGTP)
2’-deoxycytidine 5’-triphosphate (dCTP)
2’-deoxythymidine 5’-triphosphate (dTTP)

can be made synthetically via enzymes

Question 7

what type of bond joins nucelotides

Answer 7

phosphodiester bond

Question 8

direction of DNA

Answer 8

5’ -> 3’
5’ P terminus to 3’ OH terminus

Question 9

Who discovered DNA

Answer 9

James watson & Francis Crick in 1953
Based on research by Rosalind Franklin

Question 10

Structure of DNA double helix

Answer 10

Has sugar-phosphate backbone

In anti parallel orientation (5’ to 3’, other side upside down)

Major minor grooves

Held together by hydrogen bonds between base pairs (GC = 3 AT = 2)
really easy to take apart and put back together

Question 11

Complementary Base Pairing

Answer 11

AT 2 H bonds (purines)
GC 3 H bonds (pyrimadines)

explains chargaff’s rule

in humans, GC content is 40.3%
different organisms have different proportions of GC and AT
(probably through evolutionary needs)

Question 12

Three types of DNA helix

Answer 12

A-DNA = large (narrow,deep) major groove, small (wide, shallow) minor groove.
11 base pairs per turn

B-DNA = small (wide, deep) major groove, large (narrow, shallow) minor groove (more common)
Both right handed
10 base pairs per turn

Z-DNA = Left handed
No distinct major and minor groove tbh
Flat major groove
Narrow, deep minor groove
12 base pairs per turn

Question 13

Functions of types of DNA

Answer 13

B = common most predominent
A - rare, formed when not enough water around
Z - found naturally with B-DNA but only in certain regions within the strands, biologically active, but function unclear

Question 14

What is a gene

Answer 14

Segment of DNA molecule
seperated by intergenic DNA
Contiains biolofical info

Question 15

Units to measure length of DNA

Answer 15

Base pairs
BP
1000bp = 1kilobase (kb)
1000kb = 1 megabase (Mb)
6400 Mb diploid human genome
3200 Mb haploid human genome

Question 16

How long is a gene

Answer 16

Shortest genes = 100bp (tRNAs)
Longest genes - 2,400,000 bp = codes for human muscle protein dystrophin

DOESN’t contain 24,000 times more biological information
because genes are discontinuous

Question 17

What does it mean when we say genes are discontinuous

Answer 17

Split into exons - contain info to make protein
Split into introns

Question 18

What does it mean when we say genes are discontinuous

Answer 18

Split into exons - contain info to make protein
Split into intron - info not needed to make protein

Avg human gene contains 8 introns and 9 exons
Mean intron length = 3365 bp
Mean exon length = 145 bp
so intron can make up to 90% of total length

Question 19

Gene expressions

Answer 19

gene
(transcription)
RNA -> sometimes the final product and not further translated
(translation)
protein

Question 20

Functions of proteins

Answer 20

Structural - collagen, keratin
Motor - Myosin, dynein
Catalytic (enzymes) hexokinase, DNA Polymerase
Transport - hemoglobin, serum albumin
Storage - ovalbumin ferritin
Protective - immunoglobulins, thrombin
Regulatory - insulin, somatostatin

Question 21

what are the functional end products of gene expression

Answer 21

proteins & RNAs

Question 22

proportions of RNAtypes

Answer 22

4% coding RNA = mRNA
96% non coding RNA = e.g. rRNA etc.
still being discovered

Question 23

Simple multi gene family

Answer 23

all the genes are identical
these are when the gene product is needed in large amounts
e.g. ribosomal RNA genes

Question 24

complex multigene family

Answer 24

genes not identical but similar
code for similar proteins
provides proteins w/ slightly diff functions = increased organismal complexity
e.g. human globin genes

Question 25

human globin gene as complex multigene families

Answer 25

form two families:
alpha-globin gene chromosome 16 (3 types)
beta globin gene chromosome 11(5 types)

they’re expressed at different stages of development (remember Hb of higher O2 affinity needed at fetus stage - so slightly diff protein made)

Question 26

how do genes in multigene families arise

Answer 26

Gene duplication
during evolution - genes duplicate - gradually change - therefore slightly diff functions

usually the more time that’s passed, the more differences in gene duplication

Question 27

what is the molecular clock

Answer 27

the rate of which a gene changes
can be used to wokr out when a pair of genes were formed by duplication (estimate)

more of a difference in the sequence after gene duplication = more time has passed

Question 28

example of gene evolutionary tree

Answer 28

see the one for globins

Question 29

what is a pseudogene

Answer 29

genes without a function
- mutated to a point where the nucleotide sequence makes no sense
loses funciton

e.g. in the alpha globin family = 3 pseudogenes
beta globin = 1 pseudogene
so they genes are still present in sequence, but have no more function

Question 30

what is the beta-N- glycosidic bond

Answer 30

linkage between base and sugar of nucleotide