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•6.2 exit slip•Protein Synthesis 6.3!•HW
–finish worksheet–Quiz 6.1
GENE TO PROTEINTranscription and Translation
DNA determines your unique characteristics. A Review…
• DNA is the instructions for making proteins.• Proteins play a big role in everything you do and
determine most of your characteristics
Examples of Proteins
Hormones
Pigments
Muscle
Fibers
Enzymes
Cytoskeleton
Carrier Molecules
Membrane
Channels
Antibodies
Connective
2 Stages
Transcription• DNA → mRNA
Translation• mRNA → Protein
mRNA? What’s that?
DNA → mRNA• Uracil replaces Thymine
• DO NOT say A turns into U. A codes for U• The DNA does not become or mutate into the
RNA
DNA nucleotide codes for
RNA nucleotide
Adenine (A) Uracil (U)Thymine (T) Adenine (A)Guanine (G) Cytosine (C)Cytosine (C) Guanine (G)
Transcription
• The enzyme RNA polymerase builds an RNA strand complementary to the DNA
The following diagram shows the strands of DNA unwinding and RNA nucleotides being added…
This diagram just shows how the RNA strand breaks off
from the DNA template…
Where Does Transcription Begin?• At the promoter (for our simulations the
TATAA box)• Proteins called
transcription factorshelp RNA Polymerasebind to the DNA
Prokaryotes vs. EukaryotesProkaryotes• No nucleus• Transcription and
translation happen relatively simultaneously
Eukaryotes• Transcription in nucleus• mRNA edited before
translation (beyond our scope)
• mRNA leaves nucleus for translation
Translation
• The mRNA serves as instructions for assembling a protein
How?• The sequence of mRNA nucleotides
determines the order of amino acids in the protein
• Every 3 nucleotides (codon) codes for one amino acid
So the process basically works like this….
Remember Amino Acids?
Order of Amino Acids Determine Protein Structure
Due to
Side Chains
Translation Details
• Occurs in the ribosome in both prokaryotes and eukaryotes
• mRNA brings the code from transcription
• tRNA carries in amino acids one by one
• Protein is assembled
How Does the tRNA “know” Which Amino Acid to Bring?
• The anticodon on the tRNA is complementary to the codon on the mRNA
Hydrogen bonds
More Realistic View
The Start and Stop CodonsStart Codon• Begins translation• Always AUG• So Met is always the
first amino acid
Stop Codon• DOES NOT code for
an amino acid• Stops translation
You can determine which amino acid is coded for by each codon by looking at the following table:
Start Codon
• The process continues until a stop codon is reached.
• The protein is then released from the ribosome.
To make the process of translation faster and to make many copies of a protein, multiple ribosomes can move along mRNA
at once looking something like this…
Review
DNA: AGCGCTATAAGCTACGCGCAGCATTmRNA: CGAUGGCGUCGUAAtRNA: UACCGCAGC
Protein Met-Arg-Ser
Promoter
Start CodonStop Codon
Rapid Review• Transcription makes mRNA based on the DNA
– Occurs in nucleus– Begins at promoter
• Translation assembles protein based on mRNA code– With help of tRNA in ribosome– Begins at start codon. Ends at stop codon
• The structure and shape of the protein depends on the DNA sequence
Keep in mind…• Genes don’t code for
traits• They code for proteins
(or parts of proteins) that can affect traits
• i.e. they can code for a protein that makes eyes brown
• Differences in DNA determine differences in proteins = differences in physical traits.
Transcription Animation
• http://www.hhmi.org/biointeractive/dna/DNAi_transcription_vo2.html
Basic Translation Animation
• http://www.youtube.com/watch?v=1PSwhTGFMxs• http://www.hhmi.org/biointeractive/dna/DNAi_tra
nslation_vo1.html
Detailed Translation Animation
• http://www.hhmi.org/biointeractive/dna/DNAi_translation_vo2.html