Download The Genetic Code and Transcription Chapter 12 Honors Genetics

The Genetic Code and
Transcription
Chapter 12
Honors Genetics
Ms. Susan
Chabot
Molecular Genetics - From DNA to Protein
Characteristics of the Genetic Code
• mRNA is written in linear form using DNA as a
template for synthesis.
• Each “word” in the mRNA strand is composed of
a 3-letter sequence called a CODON.
• Each CODON specifies a SINGLE Amino Acid.
• There is 1 start codon for initiation of protein
synthesis and 3 stop codons for ending protein
synthesis for a specific protein.
• A given amino acid can have more than one codon
sequence.
The “Central Dogma” of Molecular Genetics
• DNA
Transcription
• mRNA
Translation
Protein
Folding
• Ribosome
There are Different RNAs with Distinct Functions
Transcription is a Key Step in Gene Expression
Transcription makes an mRNA copy of DNA.
This mRNA copy is complementary to the gene
sequence found on DNA.
DNA directs the synthesis of RNA in the nucleus.
RNA Review
RNA is a nucleic acid polymer that uses a slightly different
sugar than DNA and the base uracil in place of thymine.
RNA is Single-Stranded
Transcription
RNA polymerase acts here
The enzyme RNA polymerase opens the DNA strands and
synthesizes an RNA complement to only one of the DNA
strands.
A gene
The most important step in the control of gene
expression is WHEN to transcribe a gene.
Eukaryotic Genes are Segmented
Introns are removed from the primary transcript and
exons are spliced together to make mRNA.
In some genes, more than 90% of the pre-mRNA is
destroyed, never to appear in the mRNA.
The Genetic Language Uses 4 Letters Written
Into 3-Letter Words
What the Genetic Code Specifies:
AMINO ACIDS
Two examples
What Translation Accomplishes
The sequence of amino acids
determines the structure, and therefore
the function, of a protein.
During translation, information present in the mRNA is
read by the ribosome to synthesize a polypeptide.
Many
antibiotics
block steps in
translation
within
bacterial cells.
Translation requires:
ribosomes
mRNA
tRNA
amino acids
Ribosomes are
Complicated
Protein
Synthesizing
Machines
Translation Is a
Cyclic, Multistep
Process
Basic Genetic Mechanisms are Universal
The storage of genetic
information in DNA,
the use of an RNA
intermediate that is read
in three letter words,
and the mechanism of
protein synthesis are
essentially the same in
all organisms.
A tobacco plant
expressing the
firefly luciferase
gene.