Gene Expression

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Transcript Gene Expression

Gene Expression
From a gene to a protein
Central Dogma
• (Crick 1958)
• Determines the genetic flow of information
Central Dogma
First step: a genetic message from DNA is
to copied (transcribed) into mRNA, which
contains the code for making proteins
Second step: is to decode mRNA into a
polypeptide chain which builds a protein.
Functions of a Protein
Functions of Protein:
• Structural
– muscle, hair
• Chemical
– antibodies, hormones, enzymes (regulate
all chemical reactions in cells)
• Proteins are made, from mRNA, by joining
amino acids into long polypeptides (which
are proteins)
– There are only 20 naturally occurring amino
Review of DNA
• DNA is the genetic material
• DNA codes for different genes
– Genes are codes for a protein which
determines different traits
DNA is made up of nucleotides
Which contain:
- a phosphate group
- a sugar (deoxyribose)
- a nitrogenous base
Structure of DNA
• Involved in protein synthesis
• Made up of nucleotides:
–Nitrogenous bases (RNA only has
A, U, C, G there is no T!)
–A phosphate group
–A sugar (ribose)
Types of RNA
• There are three main types:
–Messenger RNA (mRNA)
–Transfer RNA (tRNA)
–Ribosomal RNA (rRNA)
• Messenger RNA (mRNA) carries copies of
instructions for assembling amino acids into
• Ribosomal RNA
• Along with proteins
make up ribosomes.
• During protein
construction, transfer
RNA (tRNA) transfers
each amino acid to the
• Flow of info: DNA -> mRNA
• Location: Nucleus
• mRNA is produced by copying part of the
– The mRNA leaves the nucleus and goes into
the cytoplasm and attaches to the ribosome.
• Messenger RNA is transcribed in the nucleus,
and then enters the cytoplasm where it attaches
to a ribosome.
The Genetic Code
• The genetic code is read from mRNA
– mRNA made off of a strand of DNA is read.
• mRNA is only 4 letters A, U, C, and G
• The code is read 3 letters/bases at a time
• Codon= three consecutive nucleotides
which are specific for an amino acid
• Flow of info: mRNA -> Proteins
• Location: Cytoplasm/Ribosomes
• Translation is decoding mRNA into a
polypeptide chain(protein)
Step 1 Translation
• mRNA attaches to a ribosome
• The start codon (AUG) is located by tRNA
• The matching tRNA, containing the
anitcodon UAC, will bind to AUG
• The tRNA carries the animo acid specific
to the mRNA sequence AUG, which is
Step 2
•The ribosome binds new tRNA molecules and
amino acids as it moves along the mRNA.
Step 3
As each new tRNA enters the ribosome, one leaves.
Before tRNA can leave the ribosome, the animo acids
will bond together to make a polypeptide chain
Step 4
The process continues until the ribosome
reaches a stop codon.
• Changes in genetic material
• Many have little effect on gene expression
or protein function
• A few can be harmful and then some are
– Harmful mutations can cause cancer and
genetic disorders
– Good mutation can make altered proteins
which may be beneficial in different/changing
Point Mutations
• Mutation of 1 or more nucleotides
– Substitution – changing one base, usually
only changes one amino acid
– Insertion – addition of 1 or more bases,
causes frameshifts
– Deletion – removal of 1 or more bases,
causes frameshifts
Point Mutations
Kinds of
usually affect no
more than a
single amino
Chromosomal Mutations
• Change in number or structure of a
– Deletion – loss of all or part of a chromosome
– Duplication – extra copies of parts of
– Inversion – reverse direction of parts of
– Translocation – chromosome breaks and
attaches to another
Chromosomal Mutations
• Occur during Meiosis
– Prophase I
– Anaphase I or Anaphase II
• Error in meiosis in which chromosomes fail
to separate.
Changes to Chromosome
• Monosomy 2n-1
– 45 chromosomes
– Turners (XO)
• Trisomy 2n+1
– 47 chromosomes
– Down syndrome(trisomy 21), Klinefelters
(XXY), Triple X (XXX), Jacobs (XYY)
• Polyploidy (Triploid, Tetraploid, etc)
Turners (45, XO)
• 1 in 3,000 female births
• Sterile females
Down Syndrome
•Mothers in early
20s 1 in 1,500 births
•Mothers over 35 1
in 70 births
•Mothers over 45 1
in 25 births
Klinefelters (XXY)
• 2 in 1000 male births
• Sterile males
Jacobs (XYY)
• 1 in 1000 male
• Tall
• Lower mental
• Tendency for