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Gene Expression
AS 90715 (3.3) external (for Michael)
US 8931 Describing Gene expression.
US 8932 Gene - Gene Interactions.
Concepts to cover
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The role of DNA in gene expression.
DNA Replication
Protein synthesis
Hereditary metabolic disorders
Allele Interactions
Gene gene interactions
Gene Environment interactions
Mutations
Control of gene expression (feedback
mechanisms)
The basic unit of living organisms is
the cell
The Genetic Code
• Cell Structure
• Prokaryotic cells – simple single cell
bacteria, Chromatin material (DNA) not in
nucleus, easier to study.
• Eukaryotic cells – all cells with a true
nucleus. Chromosomes in nucleus.
• www.cellsalive.com to learn about
organelles.
Control the Cell
• Proteins are responsible for
– The enzymes that catalyse all the reactions
– The structural parts (hair, muscle)
– The carriers of oxygen (haemoglobin)
– The fighters of disease (white blood cells)
– Part of cell membranes (control movement
in/out of cell)
– hormones
What controls the proteins, controls
the cell.
• The proteins organise every activity in the
cell, so if you want to make a cell do or be
something, you need to manage whatever
it is that controls the proteins.
• The genes in the chromosomes control the
proteins. Every cell has the same genes
but only the genes for the proteins being
used by the cell are turned on in that cell.
• Connect genes to
proteins –use
Agresearch DNA
presentation.
What is DNA.exe
Eukaryotic Chromosome Structure
• Refer to Manual pg 60 (old book)
• Chromatin fibres, centromere.
• Each chromosome not usually visible (is
unwound so genes can be read during normal
cell activity)
• One chromatid, forms two chromatids (during
cell division)
• Coil of chromatin wrapped around histones.
• DNA double helix.
One double stranded DNA
molecule
DNA wrapped around
a ball of histone proteins
A chromosome is highly
packaged DNA
Karyotypes
• Prepared photographs of chromosomes,
used to identify pairs of chromosomes.
• Human chromosomes in the nucleus are
not normally visible in these shapes.
• Manual pg 62 (old )
Homologous Chromosomes
• Scientists worked out that chromosomes come
in pairs,
• The pair has the same genes on them,
• So you get two versions of each gene, one on
the chromosome from the mother and one on
the chromosome from the father.
• The genes are on matching locations on the pair
of chromosomes so they are called
Homo (same ) logous (location) chromosomes.
• One breakthrough scientists made was to
work out that one pair of chromosomes
control the gender (the sex),
• so that pair was called the sex chromosomes
(XX and XY)
• The other 22 pairs are called the autosomal
chromosomes.
The sex chromosomes are not homologous.
Chromosomes and DNA
• What do we know about DNA?
Deoxyribonucleic acid
• Nucleotide
A phosphate
A sugar (deoxyribose)
A base
• Adenine, Thymine
• Cytosine, Guanine
• Base Pairs match across DNA strands to make a
double helix. (purines pair with pyrimidines)
• Kb stands for kilobases – thousands of bases to
make one gene on a chromosome.
Other nucleic acids
• Nucleic acids are a family that have the same
structure – a phosphate, sugar and bases.
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RNA
has ribose instead of deoxyribose sugar
Single strand (not double)
No T, has Uracil (U) instead.
Comes in mRNA, tRNA.
• DNA comes in mitochondrial DNA as well.
Double stranded DNA
• One strand of the DNA is called the
template strand (the one the mRNA reads
to get the code).
• The other strand is called the coding
strand ( in fact it is identical to the mRNA
in the end).
• Manual pg 68, 69.Nucleic acids
• Manual pg 76 Creating a DNA model
DNA
exon
coding region
intron
non coding region
In the exons and introns are rows and rows of
matched up nucleotides. Scientists currently
working out the order of the bases to break the
genome to identify what the DNA is doing.
• Look at a genome for a bacterial virus.
• Manual pg 70.
• The genome is only one side of the DNA
double helix bases listed.
NOW THAT WE KNOW HOW DNA
IS SHAPED
WHAT DOES IT DO?
It does two things
1 Protein synthesis
(makes proteins so the cell functions)
2 DNA replication
(makes more chromosomes when the cell is
dividing)