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From DNA to Protein
Chapter 5
Ricin and your Ribosomes
DNA and RNA
DNA has one function: It
permanently stores a cell’s
genetic information, which
is passed to offspring.
RNAs have various
functions. Some serve
as disposable copies of
DNA’s genetic message;
others are catalytic.
DNA template
Transcription
mRNA
Translation
protein
stop
Amino acid
Gly
Amino acid
Glu
Amino acid
RNA in Protein Synthesis
2 Different Kinds of RNA:

Messenger RNA (mRNA)
Contains information transcribed from DNA

Transfer RNA (tRNA)
Delivers amino acids to ribosomes
Gene Expression

Gene expression
A multistep process in which genetic
information is converted into a structural
or functional part of a cell or body
Transcription: DNA to RNA

RNA polymerase assembles RNA by
linking RNA nucleotides into a chain
Transcription: DNA to RNA
DNA template
Transcription
mRNA
Base-Pairing in DNA Synthesis
and Transcription
Fig. 14-5a, p. 218
Post-Transcriptional
Modifications
gene
exon
DNA
cap
PremRNA
intron exon intron
exon
transcription into RNA
poly-A
tail
3’
5’
snipped out
snipped out
mRNA
Fig. 14-7, p. 220
mRNA – The Messenger

Codon-A sequence of 3 mRNA
nucleotides that codes for a specific
amino acid

The order of codons in mRNA determines
the order of amino acids in a polypeptide
chain
Genetic Information
• From DNA to mRNA to amino acid
sequence
codon
Translation
2 subunits
Ribosomes
made of
rRNA &
proteins
Codons of the Genetic Code
Common Mutations


Base-pair-substitution
Deletion or insertion
THREONINE PROLINE
GLUTAMATE GLUTAMATE
LYSINE
a. Normal
Hemoglobin chain
b. Base pair
substitution
THREONINE
PROLINE
VALINE
GLUTAMATE
LYSINE
c. Frame shift
THREONINE
PROLINE
GLYCINE
ARGININE
Fig. 14-13, p. 224
What Causes Mutations?
1.
Spontaneous mutations

2.
Uncorrected errors in DNA replication
Harmful environmental agents
a. UV radiation
b. chemicals
Inherited Mutations


Mutations in somatic cells of sexually
reproducing species are not inherited
Mutations in a gamete may be inherited,
with evolutionary consequences