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Protein Synthesis
Transcription and Translation:the Central
Dogma
DNA
Transcription
RNA
Translation
Protein
RNA
 RNA: ribonucleic acid
 Carries out protein
synthesis
 Differences from DNA:
 different sugar (ribose)
 single strand
 different base
 no thymine
 URACIL instead
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
Process of Transcription
•
Transcription- process that makes mRNA from
DNA
1.
DNA unzips into 2 separate strands
A. DNA Helicase is the enzyme that breaks Hbond
2. Free floating RNA NITROGEN BASES in the
nucleus pair up w/unzipped DNA:
A. Cytosine(C) pairs with Guanine(G)
* (G) - (C)
B. Adenine (A) pairs with Uracil (U)
* (A) - (U)
C. Thymine (T) pairs with Adenine (A)
***remember (T) is only with DNA
Transcription
RNA Polymerase is the enzyme that
strings
together the complimentary strand of RNA
nucleotides .
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Transcription
DNA
ATCGTTACATGC
RNA
UAGCAAUGUACG
A-U
T-A
G-C
C-G
3. After all the pairing is done:
•
a single strand of RNA has been
produced.
Transcription
-
Genetic code from DNA is transferred to
mRNA
-The code obtained from DNA lets the mRNA
know which amino acids to pick up.
Transcription
Adenine (DNA and RNA)
Cystosine (DNA and RNA)
Guanine(DNA and RNA)
Thymine (DNA only)
Uracil (RNA only)
RNA
polymerase
RNA
DNA
Transcription
Similar to DNA Replication:
- Occur within the nucleus of eukaryotic cells.
- Both catalyzed by large, complex enzymes
- Both involve unwinding DNA
- Both involve specific base-pairing
Transcription
Different to DNA Replication:
- Cell may need hundreds or thousands of copies
of certain proteins.
- Makes a single stranded compliment of only a
segment of DNA and only when it is needed.
- Process can occur over and over again.
Translation
Converts the mRNA message into a polypeptide.
One or more polypeptides make up a protein
Translation
Nucleus
Lysine
Phenylalanine
Methionine
tRNA
Ribosome
mRNA
Start codon
mRNA
Translation
20 Amino acids are used as the “language” of
proteins.
Bases : Nucleic Acids
Amino Acids : Proteins
Translation
Codon: 3-nucleotide sequence that codes for an amino acid
* Many amino acids are coded for by more than one codon
Ex: Leu
* The first two nucleotides- generally most important in coding
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Translation
START CODON (AUG) : Methionine (MET)
STOP CODONS: UAA , UAG, UGA
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Translation
Codons must be read in the right order - reading frame
Change in the reading frame- change in the protein
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Translation
GENETIC CODE:
- Shared by almost all organisms- even viruses
- “Universal” code
- Common nature of the genetic code suggests that
almost all organisms arose from a common ancestor.
- Scientists can insert a gene from one organism into
another to make proteins
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Translation
DNA
TRY IT OUT!
TACCCGTTACGAATT
mRNA
Amino Acid
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Translation
DNA
TRY IT OUT!
TAC/CCG/TTA/CGA/ATT
mRNA
AUG/GGC/AAU/GCU/UAA
Amino Acid
Met-Gly-Asn-Ala-STOP
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Translation
MAKE A PROTEIN:
Write out a 30 base DNA sequence ( pink paper)
( Blue paper) Show DNA —> RNA —> Amino Acid sequence
Exchange pink sheet with a partner!
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Translation
Ribosomes- site where proteins are made
Small subunit: holds the mRNA strand
Large subunit: holds on to the growing protein
Translation
tRNA : Carries amino acids from the cytoplasm —> ribosome
One end is attached to a certain amino acid
Other end—> Anti-codon : recognizes a certain codon
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Translation (continued)
Growing polypeptide
chain
Ribosome
tRNA
Lysine
tRNA
mRNA
mRNA
Ribosome
Translation direction