Download 6.4 RNA - Part 2 - Translation rna_2_s12

RNA 2
Translation
Big Picture
DNA
Gene
Segment of
4 bases
Base paring DNA @ specific
location.
Double helix
Instructions for
making
Protein
Trait
Observed
physical
Characteristics
Quick Review
What does a protein do?
“Machinery” of the cell: pumps,
enzymes, contraction, cytoskeleton...
Sure...but what are they?
Proteins are...
...polymers of amino acids
A “string of beads”
Amino acids have
1. Central carbon atom
2. Amino group
3. Acid Group
4. “Side Group”
There are 20 amino acids used in proteins, all with different
“side groups.”
Proteins
Protein Chains
The order and the properties of the amino
acids of the 20 different types give proteins
their unique characteristics and abilities.
how do we get from a gene
to a protein?
It’s all about the code...
We need a code that can tell us which amino
acids to put where to get the results we want.
Genetic Code
It takes 3 DNA nucleotides to “code for” the 20
possible amino acids
1 molecule would give us how many
options?
4 different bases in one location: A or T...
4 options or 41 (not enough)
2 molecules would give us...?
AA or AT or AG or...
16 options or 42 (not enough)
3 molecules gives us...?
64 options or 43 (plenty)
Using the 64
combinations
One combination “starts” the sequence
DNA sequence:
TAC
mRNA sequence: AUG
3 combinations “stop” the sequence
DNA sequences:
ATT, ACT, ATC
mRNA sequences: UAA, UGA, UAG
Each 3-letter mRNA sequence is called a
codon.
Codons
More than one codon can code for an
amino acid
Alanine = GCU, GCC, GCA, GCG
Each codon only codes for one amino
acid.
GCU is always alanine
The redundancy, or back-up duplicates, in
the code offer some protection from errors
Amino Acids
Phenylalanine (Phe)
Leucine (Leu)
Isoleucine (Ile)
Valine (Val)
Serine (Ser)
Proline (Pro)
Threonine (Thr)
Alanine (Ala)
Tryosine (Tyr)
Histidine (His)
Glutamine (Gln)
Asparagine (Asn)
Lysine (Lys)
Glutamic Acid (Glu)
Aspartic Acid (Asp)
Cystenine (Cys)
Tryptophan (Trp)
Argenine (Arg)
Glycine (Gly)
Methionine (Met)
Start codon
Codons
Codons are like words
The letters tell you what the word means
Which amino acid to use
The words for a sentence
The combination of amino acids that
produces the working protein.
How to we Read the
Amino Acid (AA) Chart?
The chart is read by looking at the codon on the
mRNA strand
Steps:
Read the mRNA codon and then look to chart
to find the corresponding amino acid
Left,
Up,
Right
DNA Strand:
•TAC
mRNA Strand:
•AUG
Amino Acid:
•Met
(Methionine)
DNA Strand:
•TACGTAAAT
mRNA Strand:
•AUGCAUUUA
Amino Acid:
•[Met][Tyr][Leu]
How do we actually
make proteins?
Translation
Steps of Making Proteins
Transcription:
mRNA Copy
√
Translation:
Protein Synthesis
Proteins
Making Proteins
Translation:
Protein Synthesis
• We already have:
• Protein making instructions (mRNA)
• We still need:
• A Workbench
• Amino Acids
mRNA to Proteins
• To start the process, the mRNA is transported
to a ribosome (workbench)
• In the ribosome, the mRNA will provide
directions for how to make proteins
• This process is called translation
• Translation = the creation of proteins by
linking chains of amino acids together
(polymers)
• Occurs in cytoplasm or attached to RER.
The Players
•
mRNA:
•
•
tRNA:
•
•
messenger RNA
transfer RNA
Ribosomes:*
•
rRNA + Proteins
Transfer RNA: (tRNA)
It’s job is to transfer amino acids
from cytoplasm to ribosome
1. Anticodon is located on the
bottom (base pairs to mRNA
codon)
•
Must match the mRNA codon
exactly in order to pair
2. Amino acid attaches to the top
•
The specific amino acid that the
tRNA carries is determined by its
anticodon
Ribosome
The ribosome has two major parts (called subunits)
The large and small subunits
Both are made from proteins and ribosomal RNA
(rRNA)
mRNA is pulled through and read only when the
subunits join together
Disclaimer:
You are not expected to know the
exact details of Translation, but it
sometimes is helpful to see how the
process works to better understand it.
I will tell you what you should and
should not know.
Translation
Three parts
Initiation
Elongation
Termination
Initiation
1. Ribosome locks around the mRNA
2. tRNA pairs with start codon AUG,
• tRNA amino acid is Met (methionine)
Elongation
•
Codon Recognition, an
incoming tRNA binds to
the codon in right site
• Bond formation, the
ribosome forms a bond
between the new amino
acid and the growing
protein chain
Elongation Continued
the tRNA in the right site
is moved to the middle
site, taking the mRNA
along with it, middle site
open to next tRNA
The tRNA in the right site
moves to the left site and
is released from the
ribosome, the ribosome
shifts the mRNA by one
codon
Termination
• When the ribosome reaches the termination codon
(UAG,UAA,UGA) on the mRNA
• The protein chain in released
•
Subunits separate
Practice
Turn to your neighbor...
Describe the summary of translation in
your own words
Switch and have the other neighbor try it
Be Prepared to share your summary with
the class
Translation Summary
mRNA is sent from nucleus to cytoplasm
Ribosome attaches to the mRNA in the cytoplasm
tRNA’s bring the amino acids to the ribosome
It is the anticodon of the tRNA that determines
which AA the tRNA carries
The first tRNA brings the AA Met to the start
codon
Translation Summary
The mRNA is read by the ribosome (pulled like a
tape)
The mRNA codon is matched to the tRNA anticodon
If the codon & anticodon match, the AA is added
to the protein chain
When the stop codon is reached on the mRNA, the
ribosome separates and the protein is released
Put it all together
Take out a half sheet of paper
Explain how a protein is made beginning
from DNA
Be sure to include Transcription &
Translation
This is a great level 3 question
Practice
•
Protein Synthesis
•
Snorks