Transcript 12-3 RNA and Protein Synthesis

DNA To RNA To Proteins
Transcription, Translation → Proteins
Which is
The Central Dogma of Biology
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The Structure of RNA
• Long Chains of Nucleotides
– 5 Carbon Sugar ( Ribose )
– Phosphate Group
– Nitrogenous Base
• A, G, C, U ( no T )
– Single Stranded
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Types of RNA
RNA Mostly For Protein Synthesis
Three Types of RNA
Messenger RNA, mRNA
Ribosomal RNA, rRNA
Transfer RNA, tRNA
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Types of RNA
mRNA
A Copy of the Recipe in the DNA. Transports the
Recipe to the Ribosome.
rRNA
Part of ribosome.
It Reads the Recipe in the mRNA
Puts the ingredients together
tRNA
Transports Amino Acids (the ingredients) from
cytoplasm to the Ribosomes in the Order
Needed to make the Protein (the Cookies)
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Transcription (mRNA)
The process of copying the DNA
nucleotide sequence into a
complementary sequence of RNA
( copying the recipe)
Requires a special enzyme:
RNA Polymerase
(Transcription Rate= ~60 nucleotides/second)
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RNA Polymerase
DNA
DNA
RNA
Polymerase
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Transcription
Key Concept:
During transcription, RNA
polymerase binds to DNA and
separates the DNA strands. RNA
Polymerase then uses one strand
of DNA as a template to
assemble nucleotides into RNA
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Transcription
Promoters
– Regions on DNA that show where
RNA Polymerase must bind to
begin the Transcription of RNA
– Specific base sequences act as
signals
– Other base sequences indicate
stopping points
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Transcription
The Devil is in the Details
RNA Splicing
After the DNA is transcribed into
mRNA:
Editing must be done to the mRNA
chain to make the mRNA functional
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Transcription
The Devil is in the Details
Introns need to be removed
• These are non-functional segments of the
mRNA strand copied from the DNA
• Snipped out of the chain in the nucleus
Exons need to be glued back together
• These segments contain the real recipe and
need to be reconnected to make the real,
functional mRNA
This Process is called: mRNA Splicing
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mRNA Splicing
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The Genetic Code
Proteins are:
–long chains of amino acids.
• There are 20 different amino acids
– The order of amino acids in the
protein determine its shape and
function
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The Genetic Code
There are 20 amino acids
but only 4 bases in RNA.
So, How Can You Design A Code?
Adenine
Cytosine
Guanine
Uracil
A
C
G
U
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RNA
Bases
The Genetic Code
The genetic code consists of
“words” three bases long
Each “word” is called a Codon:
A codon is three consecutive
nucleotides that code for a single
amino acid
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The Genetic Code
For Example:
UCGCACGGU = RNA Sequence
UCG - CAC - GGU = Codons
UCG
CAC
GGU
codes for Serine
codes for Histidine
codes for Glycine
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The Genetic Code
If you have 4 Bases and….
Codons are defined with 3 Bases…..
How many combinations of 3 can you make?
There Are 64 Possible 3-base codons
Since there are only 20 amino acids,
some amino acids are represented by
multiple codons
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Code Wheel
Table On
Page 303
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Code Table
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8 Essential Amino Acids
Essential AA = An Amino Acid That Can NOT Be Made, It Must Be Eaten
Essential AA
Meats
Grains
Legumes
Methionine


Tryptophan


Phenylalanine



Leucine



Threonine



Valine



Isoleucine


Lysine


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Translation
Translation is the process of
decoding the mRNA and chaining
Amino Acids together into the
polypeptide chain
(making the protein)
(See pages 245-247)
• Ribosomes
– Read mRNA and construct the proteins
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Translation
Step A
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Translation
Step B
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Translation
Step C
Step C
– Ribosome connects the
amino acids together as
they come into the
ribosome
– Ribosome disconnects
the the 3rd amino acid
from the ribosome to
float into the cytoplasm
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Translation
Step D
• Step D
– Polypeptide chain
grows until the
mRNA STOP Codon
is reached
– The ribosome then
releases the
polypeptide chain
into the cytoplasm
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The Roles of DNA & RNA
DNA =
The Cookbook
mRNA =
A copy of the
recipe from “The
Cookbook”
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Genes & Proteins
• Genes are instructions for
assembling proteins (recipes in a cookbook)
• Proteins (the cookies from the recipe) are
enzymes that catalyze and regulate
chemical reactions
– Pigments, antigens, regulators
– Proteins are the keys to biological
function
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