Download Transcription and Translation ppt

Topic: DNA Transcription and
Translation
Aim: How are proteins made from
DNA?
DNA
RNA
Amino Acids(Proteins)
• DNA contains the genetic information to
make amino acids
• Amino acids combine to make proteins
• These proteins determine the physical traits
of an organism and control cellular functions.
• Proteins do everything,
and DNA gets all the
credit!
• Think of them as tiny minions
who do all the work
RNA vs DNA
 RNA: ribonucleic acid
 Carries out protein synthesis
 Differences from DNA:
 different sugar (ribose)
 single strand
 different base
 no thymine
 URACIL instead
DNA and Protein Synthesis
3 Types of RNA:
• Messenger RNA:
(mRNA) carries nucleotide
sequence from nucleus to
ribosome
• Transfer RNA: (tRNA)
picks up amino acid in
cytoplasm and carries
them to ribosome
• Ribosomal RNA:
(rRNA)found in ribosome,
joins mRNA and tRNA;
forms protein
Steps of Transcription
Transcription- process that makes mRNA from DNA
1. DNA unzips into 2 separate strands
A. DNA Helicase is the enzyme that breaks H-bond
2. Free floating RNA NITROGEN BASES in the nucleus
pair up w/unzipped DNA NITROGEN BASES:
A. Cytosine(C) pairs with Guanine(G)
* (G) with (C)
B. Uracil(U) pairs with Adenine(A)
* (A) with (U)
C. Thymine (T) pairs with Adenine (A)
***remember (T) is only with DNA
3. After all the pairing is
done:
• a single strand of RNA
has been produced.
4. Genetic code from DNA
is transferred to mRNA
5. The code obtained from
DNA lets the mRNA know
which amino acids to pick
up:
• code is a set of 3
nitrogen bases = Codon
Transcription
Adenine (DNA and RNA)
Cystosine (DNA and RNA)
Guanine(DNA and RNA)
Thymine (DNA only)
Uracil (RNA only)
RNA
polymerase
DNA
RNA
DNA
RNA
Practice making mRNA using the DNA template
Remember:
RNA does not
have
T(Thymine); it’s
replaced by
U(Uracil)
A T T A C A
C U A A U G U
mRNA
Transcription Practice
Transcript the following segment of DNA into RNA
DNA: A U G T T T A G A C A T G G C
RNA:
Translation
• Conversion of RNA into amino
acid sequence that makes a
protein
• The mRNA leaves the nucleus and
enters the cytoplasm
• Ribosomes attach to mRNA
• tRNA (carrying anti-codon) picks
up the correct amino acids and
carries them to the mRNA strand
forming the protein
Ex:
– tRNA carries GAU (anti-codon)&
looks for CUA on mRNA
DNA and Protein Synthesis
• Codon: three bases code for a specific protein:
ex: AAA = Lysine
• The codons code for 20 amino acids
• Just like the alphabet has 26 letters to make all
the words we know, the 20 amino acids make
all the different proteins found in living
organisms
• The codons are the template for protein synthesis,
which takes place on the ribosomes (rRNA) in the
cytoplasm
Translation: changing mRNA into Amino Acids (Proteins)
• Amino acids are linked together in the same
order as the codons , creating a protein chain
• Just like linking letters to make words, linking
amino acids makes proteins
mRNA
CUA AUG UGC
Amino
Acid
Amino
Acid
Amino
Acid
DNA and Protein Synthesis - Summary
Translation
Nucleus
Lysine
Phenylalanine
Methionine
tRNA
Ribosome
mRNA
Start codon
mRNA
Translation (continued)
Growing polypeptide
chain
Ribosome
tRNA
Lysine
tRNA
mRNA
mRNA
Ribosome
Translation direction
• Summary of
transcription
and
translation
TRANSCRIPTION
DNA
mRNA
RNA
polymerase
Stage 1 mRNA is
transcribed from a
DNA template.
Amino acid
TRANSLATION
Enzyme
Stage 2 Each amino
acid attaches to its
proper tRNA with the
help of a specific
enzyme and ATP.
tRNA
Initiator
tRNA
mRNA
Figure 10.15
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Anticodon
Large
ribosomal
subunit
Start
Codon
Small
ribosomal
subunit
Stage 3 Initiation of
polypeptide synthesis
The mRNA, the first
tRNA, and the
ribosomal subunits
come together.
New
peptide
bond
forming
Growing
polypeptide
Codons
Stage 4 Elongation
A succession of tRNAs
add their amino acids to
the polypeptide chain as
the mRNA is moved
through the ribosome,
one codon at a time.
mRNA
Polypeptide
Stop Codon
Figure 10.15 (continued)
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Stage 5 Termination
The ribosome recognizes
a stop codon. The polypeptide is terminated and
released.
Lesson Summary
Transcription: changing DNA into RNA
– How to change DNA into RNA?
• Answer: Just follow Chargaff’s Rule:
– A always pair with T
– C always pair with G
– However, RNA does not have T(Thymine), it has
U(Uracil)
Translation: changing mRNA
into amino acids (proteins)
How to change mRNA into amino acids?
Answer:
Step 1: remember, 3 bases equal 1 codon
Step 2: look at the universal amino acids chart
to translate into the correct amino acids.