1. Chapter 13: Protein Synthesis

2. Chapter 13 Protein Synthesis - Overview
The DNA of the gene is transcribed into RNA
Which is translated into protein
The flow of genetic information from DNA to RNA to Protein is called the CENTRAL DOGMA
DNA
Transcription
RNA
Translation
Protein

3. Chapter 13 Protein Synthesis (Overview)
Central Dogma - FLOW IS FROM DNA TO RNA TO PROTEIN

4. FLOW IS FROM DNA TO RNA TO PROTEIN
Chapter 13 Protein Synthesis (Overview)
FLOW IS FROM DNA TO RNA TO PROTEIN
Genes on DNA are expressed through proteins, which provide the molecular basis for inherited traits
A particular gene, is a linear sequence of many nucleotides
Specifies a polypeptide (long protein made of amino acids)

5. Chapter 13 Protein Synthesis (Overview)
Genes - discrete units of hereditary information comprised of a nucleotide sequence found in a DNA molecule.

6. 13-1 Messenger (mRNA) Monomer: nucleotide Parts of a mRNA Nucleotide
Ribose Sugar
Phosphate
Nitrogenous Base
Three main differences between mRNA and DNA
Ribose instead of deoxyribose
mRNA is generally single stranded
mRNA has uracil in place of thymine (U instead of T)

7. 13.1 RNA
Three Types of RNA
Messenger RNA (mRNA) – carries copies of genes (DNA) to the rest of the cell.
Ribosomal RNA (rRNA) – make up the ribosomes.
Transfer RNA (tRNA) – transfers the amino acids to the ribosomes as specified by the mRNA

8. 13.1 TRANSCRIPTION: The process of making mRNA from DNA
Why do you need this process?
Location of DNA? Nucleus
Location of Ribosome? Cytoplasm
mRNA takes code from DNA in the nucleus to the cytoplasm
Strand to be transcribed T A C
DNA A T G
Transcription A U G A A G U U U U A G
RNA
Start condon
Stop condon
Translation
Polypeptide
Met
Lys
Phe

9. 13.1 Transcription produces genetic messages in the form of mRNA
A close-up view of transcription
RNA
polymerase
RNA nucleotides
Direction of
transcription
Template
Strand of DNA
Newly made RNA T C A G U

10. 13.1 In the nucleus, the DNA helix unzips
And RNA nucleotides line up along one strand of the DNA, following the base pairing rules
As the single-stranded messenger RNA (mRNA) peels away from the gene
The DNA strands rejoin
RNA
polymerase
RNA nucleotides
Direction of
transcription
Template
Strand of DNA
Newly made RNA T C A G U

11. Transcription of a gene
RNA polymerase
DNA of gene
Transcription of a gene
Initiation
Elongation
Termination
Promoter
DNA
Terminator
DNA
1 Initiation
Area shown
In Figure 10.9A
2 Elongation
Growing
RNA
3 Termination
Completed RNA
RNA
polymerase

12. 13.1 Eukaryotic mRNA is processed before leaving the nucleus
Exon Intron Exon Intron Exon
DNA
Cap
Transcription
Addition of cap and tail
RNA
transcript
with cap
and tail
Introns removed
Tail
Exons spliced together
mRNA
Coding sequence
Nucleus
Cytoplasm
13.1 Eukaryotic mRNA is processed before leaving the nucleus
Noncoding segments called introns are spliced out leaving only the coding exons
A 5’ cap and a poly A tail are added to the ends of mRNA
Cap and tail protect mRNA 5’ 3’

13. T C C A A T A U T C T G U G A C C A U C C A C G A A T A G G T T
Direction of
transcription

15. 13.2 Translation tRNA molecules Growing polypeptide (protein)
mRNA
Small
subunit
Growing polypeptide (protein)
Large subunit

16. 13-2 Protein Synthesis - Translation
Translation is defined as going from mRNA to protein
tRNA which have amino acids attached are going to the ribosome.
What are amino acids? monomers of proteins
Does the order of amino acids matter? Yes, they must be in order for the protein to fold correctly.
How does the correct tRNA (with amino acid attached) bind to the mRNA? The tRNA contains an anticodon which matches up with the mRNA sequence (codon).

17. Transfer RNA (tRNA) molecules serve as interpreters during translation
Takes place in the cytoplasm
A ribosome attaches to the mRNA and translates its message into a specific polypeptide aided by transfer RNAs (tRNAs)
tRNAs can be represented in several ways
Amino acid
attachment site
Amino acid attachment site
Hydrogen bond
RNA polynucleotide chain
Anticodon
Anticodon

18. 13.2 Translation Each tRNA molecule A specific amino acid
Is a folded molecule bearing a base triplet called an anticodon on one end
A specific amino acid
Is attached to the other end
Amino acid
attachment site
Anticodon

19. Ribosomes build polypeptides (proteins)
13.2 Translation
Ribosomes build polypeptides (proteins)
A ribosome consists of two subunits
Each made up of proteins and a kind of RNA called ribosomal RNA
Translation at Ribosome
tRNA molecules
mRNA
Small
subunit
Growing polypeptide
Large subunit

20. 13.2 Translation The subunits of a ribosome
Hold the tRNA and mRNA close together during translation
tRNA-binding sites
Large subunit
Next amino acid to be added to polypeptide
Growing polypeptide
tRNA
mRNA- binding site
mRNA
Small subunit
Codons

21. An initiation codon marks the start of an mRNA message
mRNA, a specific tRNA, and the ribosome subunits assemble during initiation
Met
Initiator tRNA 1 2
mRNA
Small ribosomal subunit
Start codon
Large ribosomal subunit
A site U A C
A U G
P site

22. Elongation adds amino acids to the polypeptide chain until a stop codon terminates translation
Once initiation is complete amino acids are added one by one to the first amino acid
The mRNA moves a codon at a time
A tRNA with a complementary anticodon pairs with each codon, adding its amino acid to the peptide chain

23. Each addition of an amino acid
Occurs in a three-step elongation process
Amino acid
Polypeptide
P site
A site
Anticodon
mRNA
Codons 1
Codon recognition
mRNA movement
Stop codon 2
Peptide bond formation
New
Peptide bond
Figure 10.14 3
Translocation

24. Figure out the exact sequence of amino acids needed
Take the DNA and transcribe it into mRNA
Example: TAC ATA CTA GCG ACT
mRNA:
Take the mRNA sequence and decode it using the codon chart.
AUG
UAU
GAU
CGC
UGA
AUG = MET
UAU = TYR
GAU = ASP
CGC = ARG
Animation

25. 13.3 Mutations
Mutations – heritable changes in genetic information (changes to the DNA sequence)
Two types - gene and chromosomal mutations
Mutations can be caused by chemical or physical agents (mutagens)
Chemical – pesticides, tobacco smoke, environmental pollutants
Physical – X-rays and ultraviolet light

26. 13.3 Mutations Gene mutations
Point Mutation: mutations that affect a single nucleotide
Frameshift mutation: shift the reading frame of the genetic message.
Can change the entire protein so it doesn’t work
Gene Mutations Explained

27. 13.3 Mutations

28. 13.3 Chromosomal Mutations
Chromosomal mutation: mutation that changes the number or structure of chromosomes.

29. 13.3 Chromosomal Mutations
Types of chromosomal mutations:
Deletion: The loss of all or part of a chromosome
Duplication: A segment is repeated
Inversion: part of the chromosome is reverse from its usual direction.
Translocation: one chromosome breaks off an attaches to another chromosome.