Transcript Lect2 Genetics

Genetics
Nicky Mulder
Life as we know it
is specified by
genomes
They hold all the necessary
info to grow and function
Copyright-Anna Kramvis
2
Genomes
Prokaryotes
Eukaryotes
History of
genetics
1953
Watson and
Crick
discover
structure of
the DNA
double helix
Mendel’s genetics
Studied inheritance of seed
change –characterized dominant
and recessive phenotypes
Some genetics concepts
Diploid –two copies of each chromosome
 Two copies of each gene (allelles), if the
same then homozygous, if different –
heterozygous
 Alleles can be wild type or mutant
 Interactions between alleles can be
dominant or recessive

Central Dogma
DNA
Genomes
RNA
Protein
RNA genomes
Some viral genomes are RNA
 Retrotranscribed into DNA

DNA genomes
Prokaryotes
Composed of nucleic acids
Eukaryotes
Nucleic Acids -DNA





Deoxyribonucleic acid
Nuclear material, found in nucleus
Double stranded
Sugar: 2’-deoxyribose
Nucleotides




Adenine (A)
Cytosine (C)
Guanine (G)
Thymine (T)
Copyright-Anna Kramvis
11
Nucleic Acids -RNA






Ribonucleic acid
Genome of some viruses
Found in cytoplasm
Single stranded
Sugar: ribose
Nucleotides




Adenine (A)
Cytosine (C)
Guanine (G)
Uracil (U)
Nucleotides
purine
phosphate
OOO5’
γ
β
α
O- P O- P O- P O CH2
O
O
O
4’C
H
H
3’ C
pyrimidine
base
O
H
C1’
X
H
C 2’OH
OH
H
deoxyribonucleotides
Ribonucleotides
–extra OH
sugar
Bases
Copyright-Anna Kramvis
14
From nucleotide to ssDNA
Sense strand
= mRNA
http://haplogroup-i.com/img/DNA2.gif
Copyright-Anna Kramvis
15
Base pairing
Hydrogen
bonds
AT –weaker
bond (2 versus
3 for GC)
www.mun.ca
Copyright-Anna Kramvis
16
Representation of sequences

String of letters (ACGT) usually written 5’3’
5’-ATGCGTGGCCTAAACGTTCAGGTCGA-3’
3’-TACGCACCGGATTTGCAAGTCCAGCT-5’
Reverse complement = reverse strand written 5’ to 3’
Sequence formats: Fasta
> [title]
[sequence]
>example sequence
GGAAAATTAGATGCATGGGAAAAAATTA
GGATTAGACAAGATGGGAAACCGCATTA
Sequence formats: GenBank
LOCUS
525-42
1588 bp
DEFINITION 525-42 1588 bp
TITLE
525-42
FEATURES Location/Qualifiers
exon
39..70
/note="exon1 is believed to have an alternative splice donor site"
ORIGIN
1
51
101
151
ATGTT
AGGGG
AGCTG
TGTAA
AAGAG
GAAAG
GAAAG
ACAAA
GGGGA
AAATG
ATTTG
TAATG
AAATT
CTATA
CACTT
NAACA
AGATG
NGATA
AACCC
GATAC
CATGG
AAACA
TGGCC
AACCA
GAAAA
CCTAG
TTTTA
GCTCT
AATTA
TATGG
GAGAC
TCAGA
GGTTA
GCAAG
ATCAG
CAGGA
AGGCC
CAGGG
ANGGC
ACAGA
DNA structure continued
Base pairs stack into a helix
 Alternating sugars and phosphates form
backbone

www.dkimages.com
Double helix
DNA supercoiling
DNA denaturation
Unwinding of the strands and breaking of
base pairs
 Achieved by heat
 Denaturation temperature depends on
AT/GC content
 Required for replication, transcription, etc.
 DNA can also be degraded by
exonucleases

Central dogma of molecular biology
http://www.cem.msu.edu/~reusch/VirtualText/nucacids.htm
Copyright-Anna Kramvis
24
DNA replication
DNA polymerase can only extend 5’ to 3’. Leading strand is generated
normally, lagging strand goes opposite way so is done in ‘Okazaki’
fragments
cellbiology.med.unsw.edu.au
Copyright-Anna Kramvis
25
DNA repair and recombination
DNA polymerases can make mistakes ->
mutations
 DNA repair mechanisms
 Recombination can occur –cutting out and
insertion of pieces of DNA
 These can all leads to changes in genetic
material and thus changes in phenotype!

Base pairing exercise
1.Determine the complementary strand for the following
sequences:
•5’ATGCCATTAGCTTAGCATTGGAAAGTCATGCCATG3’
•5’CATCGGTAACTAGCTAATGGCCTACTGCCATGCCT3’
2. Determine the reverse complement of the strands above.
3. Transcribe the above sequences into RNA.
4. Work out the percent GC content. Which strand will have
stronger bonding between the two strands?
Copyright-Anna Kramvis
27
Additional questions
Which of these sequences will have the
higher denaturation temperature?
1) ATATCATATGATATGTA
2) CGGTACTCGCTCAGGT
 The base composition of a sequence was
determined, there are 20% adenines, what
is the % cytosine?
