Module 1 - DNA Structure Flashcards
Why is DNA important>
Vital for all living things
Hold instructions for an organisms development, survival and reproduction
Long term storage = very stable
Role of genes in cell
- Units of biological info
- Units of inheritence
Nucelotide Structure
- 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
Bases
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)
Names of 4 nucleotides
2’-deoxyadenosine 5’-triphosphate (dATP)
2’-deoxyguanosine 5’-triphosphate (dGTP)
2’-deoxycytidine 5’-triphosphate (dCTP)
2’-deoxythymidine 5’-triphosphate (dTTP)
Names of 4 nucleotides
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
what type of bond joins nucelotides
phosphodiester bond
direction of DNA
5’ -> 3’
5’ P terminus to 3’ OH terminus
Who discovered DNA
James watson & Francis Crick in 1953
Based on research by Rosalind Franklin
Structure of DNA double helix
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
Complementary Base Pairing
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)
Three types of DNA helix
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
Functions of types of DNA
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
What is a gene
Segment of DNA molecule
seperated by intergenic DNA
Contiains biolofical info
Units to measure length of DNA
Base pairs
BP
1000bp = 1kilobase (kb)
1000kb = 1 megabase (Mb)
6400 Mb diploid human genome
3200 Mb haploid human genome
How long is a gene
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
What does it mean when we say genes are discontinuous
Split into exons - contain info to make protein
Split into introns
What does it mean when we say genes are discontinuous
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
Gene expressions
gene
(transcription)
RNA -> sometimes the final product and not further translated
(translation)
protein
Functions of proteins
Structural - collagen, keratin
Motor - Myosin, dynein
Catalytic (enzymes) hexokinase, DNA Polymerase
Transport - hemoglobin, serum albumin
Storage - ovalbumin ferritin
Protective - immunoglobulins, thrombin
Regulatory - insulin, somatostatin
what are the functional end products of gene expression
proteins & RNAs
proportions of RNAtypes
4% coding RNA = mRNA
96% non coding RNA = e.g. rRNA etc.
still being discovered
Simple multi gene family
all the genes are identical
these are when the gene product is needed in large amounts
e.g. ribosomal RNA genes
complex multigene family
genes not identical but similar
code for similar proteins
provides proteins w/ slightly diff functions = increased organismal complexity
e.g. human globin genes
human globin gene as complex multigene families
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)
how do genes in multigene families arise
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
what is the molecular clock
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
example of gene evolutionary tree
see the one for globins
what is a pseudogene
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
what is the beta-N- glycosidic bond
linkage between base and sugar of nucleotide
