Gene expression

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Gene expression
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Have you ever wondered how a frog grows?
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Native male frogs sit on the eggs and the young
froglets hatch almost fully formed.
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Why are their parts where they are?
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The answers lie in their cells.
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In particular the answer can be found in their
genetic material.
A right handed helix
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Lets revisit how we know that DNA is
important. Streptococcus pneumoniae
S smooth (virulent)
R rough (avirulent)
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DNA is the genetic material - Griffith 1928
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Avery, MacLeod McCarty 1944

• Chemically characterised the transforming
  extract from virulent cells observed by Griffith
• Removed the protein from transforming extract
• and it still transformed
• Removed RNA
• extract still transformed
• Removed DNA
• prevented transformation
• Therefore transforming substance was DNA
• Biochemically characterised the transforming
  extract, all its properties were consistent with
  DNA
• High Mw (centrifugation)
• High charge (electrophoresis)
• Characteristic UV absorbance
• Chemical analysis, ratio of nitrogen to phosphorus

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Hershey-Chase 1952

• Left, T2 virus protein radioactively labelled 35S
• Radioactivity outside
• Right T2 virus DNA radioactively labelled 32P
• Radioactivity inside
• THEREFORE genetic material infecting E.coli was
  DNA and not protein
• Genes are made from DNA (except some RNA viruses)

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Genes are encoded within DNA
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What is a gene?
Classical molecular gene A stretch of DNA
sequence that codes for a particular protein that
has a particular function.(10,11) This can be an
interrupted sequence within a chromosome.
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The gene concept has changed over time
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Other definitions of a gene
Evolutionary gene any portion of chromosomal
material that potentially lasts for enough
generations to serve as a unit of natural
selection.(39) As such a gene is an inherited
unit which is somewhere between a nucleotide and
a chromosome. Systemic Concept The gene is a
combination of (one or more) nucleic acid (DNA or
RNA) sequences, defined by the system (the whole
cell, interacting with the environment, or the
environment alone, in sub-cellular or
pre-cellular systems), that gives origin to a
product (RNA or polypeptide).(57)
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The central dogma
(Genotype)
(Phenotype)
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Transcription is the first step in the process.
http//vcell.ndsu.nodak.edu/animations/transcripti
on/advanced.htm
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How many genes does it take to make a person?
20,000-25,000
26,000
19,000
13,000
6,000
4,000
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DSCAM one gene 38,016 mRNAs An immunoglobulin
(Ig) superfamily member an axon guidance receptor
Drosophila melanogaster Dscam gene contains 115
exons spanning 60,000 bp 20 exons are
constitutively spliced (open boxes) and 95 exons
are alternatively spliced (shaded
boxes). Alternatively spliced exons are orgnized
into 4 clusters (exons 4,6, 9, 17) that contain
12, 48, 33 and 2 alternative exons each. Exons in
each cluster are spliced in a mutually exclusive
manner. Celotto Graveley 2001 Genetics
159599-608
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Immunoglobulin genes recombine within the DNA.
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So what if nuclei are the wrong shape?
85 mm
16 mm
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More or less matters!
Patau
Klinefelters (XXY)
Turners (X)
Edwards
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Albert Einstein (1955)
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30-35 of cells are aneuploid
4 aneusomy for chr 21
Affects survival, proliferation potential, and
protein imbalances
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Copy number affects your weight
Falchi et al. (2014) Nat Genetics 46492-498
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How big is a vertebrate cell?
http//medicalpicturesinfo.com/human-cell/
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Progeria (Hutchinson-Gilford progeria)
Children with this disease typically have a
stroke or heart attack caused by severe
atherosclerosis at an average age of 13 years.
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Nuclei in Progeria are the wrong shape.
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Shape directly affects the genes that are turned
on.
31 of the altered genes affect vasculature and
atherosclerosis 22 of the altered genes affect
skeletal, limb and cartilage
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Defects in transcription can cause problems. Who
amongst us is lactose intolerant?
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Lactase is encoded by a single gene
LCT gene 17 exons Chr 2q21
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The frequency of lactase persistence varies
dramatically in different populations.
Swallow Annu Rev Genet 200337197-219
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Pastoralists and milk drinkers tend to have
higher frequencies of lactase persistence than
nonpastoralists
Swallow Annu Rev Genet 200337197-219
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Translation is important too.
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tRNA the adapter
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What is the genetic code?
Redundant codons are all synonyms for the same
protein building block.
Degenerate codons differ in their third
positions e.g. both GAA and GAG code for the
amino acid glutamic acid.
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The genetic code is not always the same
Cys Euplotes
Trp Mycoplasma Spiroplasma
Gln Ciliates Acetabularia
Ser Candida
Nons. Mycoplasma
Nons. Micrococcus
Nons. Micrococcus
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Some people cant use Glucose.Typically they
have mutations in GLUT1
These mutations occur because the codons are
changed.
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GLUT1 mutations are often in helix 4
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Mitochondria in a mouse myoblast cell
Mitochondria are red Actin filaments are
green Nucleus is blue
Image taken by James Markworth (Liggins Institute)
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Differences in the human nuclear and
mitochondrial genetic codes
Trp
Met
Stop
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Protein structure is important as well.
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Prions and Alzheimers disease are examples of
pathological protein misfolding
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(No Transcript)
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Whats different between these bears?
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Polar bears and Brown Bears Divereged 479-343 kya
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Polar bears are adapted to high fat diets

• Lipids are the predominant energy source
• The polar bear has a lipid-rich diet (i.e. seals)
  throughout life.
• Extreme cholesterol levels
• Humans lt5.2 mmol/l
• Polar bear female 8.581.31 (n20)
• Male 6.61 2.06 (n20)
• Polar bear milk contains 27 fat
• Up to 50 of individuals body weight is adipose
  (subcutaneous and around organs)

Modified from Liu et al. Population genomics
reveal recent speciation and rapid evolutionary
adaptation in Polar bears. Cell (2014) 157,
785-794 and Ombostad, I. (2012) Relationships
between persistent organic pollutants (POPs) and
plasma clinical-chemical parameters in polar
bears (Ursus maritimus) from Svalbard, Norway.
Student thesis (Trondheim, Norway Norwegian
University of Science and Technology).
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The environment is affecting the genes that Polar
bears have.
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Polar bears have seven missense substitutions in
the LYST gene
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Chediak-Higashi syndrome Autosomal
recessive Mutation of lysosomal trafficking
regulator (LYST)
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What do Chimo and a Polar bear have in common?
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Lyst affects melanosome maturation The
organelle that is involved in synthesis, storage
and transport of melanin
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White fur is common in the arctic beluga
whales, polar bears, arctic hare, arctic fox
but not all due to Lyst mutations. Confers a
selective advantage?
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