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 in decoding a genetic message
from DNA is to copy (transcribe) it into
mRNA, which contains the code for
making proteins
Second step in decoding, 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
• Proteins are made, from mRNA, by joining
amino acids into long polypeptides (which
are proteins)
– There are only 20 naturally occurring amino
acids
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
RNA
• Involved in protein synthesis
• Made up of nucleotides:
–A phosphate group
–A sugar (ribose)
–Nitrogenous bases (RNA only has
A, U, C, G there is no T!)
Types of RNA
• There are three main types:
–Messenger RNA (mRNA)
–Transfer RNA (tRNA)
–Ribosomal RNA (rRNA)
mRNA
• Messenger RNA (mRNA) carries copies of
instructions for assembling amino acids into
proteins.
rRNA
• Ribosomes are made
up of proteins and
ribosomal RNA
(rRNA).
tRNA
• During translation,
transfer RNA (tRNA)
transfers each amino
acid to the ribosome.
Transcription
• Flow of info: DNA -> mRNA
• Location: Nucleus
• mRNA is produced by copying part of the
DNA
• Where does the mRNA go?
– Cytoplasm/Ribosomes
Transcription
• 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 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 animo acid
Codons
Translation
• 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
methionine
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.
Mutations
• Changes in genetic material
• Many have little effect on gene expression
or protein function
• A few can be harmful and then some are
good
– Harmful mutations can cause cancer and
genetic disorders
– Good mutation can make altered proteins
which may be beneficial in different/changing
environments
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
Mutations
•Substitutions
usually affect no
more than a
single amino
acid.
Chromosomal Mutations
• Change in number or structure of a
chromosome
– Deletion – loss of all or part of a chromosome
– Duplication – extra copies of parts of
chromosomes
– Inversion – reverse direction of parts of
chromosomes
– Translocation – chromosome breaks and
attaches to another
Chromosomal Mutations
• Occur during Meiosis
– Prophase I
– Anaphase I or Anaphase II