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PROTEIN SYNTHESIS

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Protein Synthesis The production (synthesis) of proteins. 3 phases: 1. Transcription 2. RNA processing 3. Translation Remember: DNA RNA Protein DNA RNA ... – PowerPoint PPT presentation

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Title: PROTEIN SYNTHESIS


1
PROTEIN SYNTHESIS
2
Protein Synthesis
  • The production (synthesis) of proteins.
  • 3 phases
  • 1. Transcription
  • 2. RNA processing
  • 3. Translation
  • Remember DNA ? RNA ? Protein

3
DNA ? RNA ? Protein

Eukaryotic Cell
4
DNA ? RNA ? Protein

Prokaryotic Cell
5
Question
  • How does RNA (ribonucleic acid) differ from DNA
    (deoxyribonucleic acid)?

6
RNA differs from DNA
  • 1. RNA has a sugar ribose
  • DNA has a sugar deoxyribose
  • 2. RNA contains uracil (U)
  • DNA has thymine (T)
  • 3. RNA molecule is single-stranded
  • DNA is double-stranded

7
1. Transcription


Eukaryotic Cell
8
1. Transcription
  • The transfer of information in the nucleus from a
    DNA molecule to an RNA molecule.
  • Only 1 DNA strand serves as the template
  • Starts at promoter DNA (TATA box)
  • Ends at terminator DNA (stop)
  • When complete, pre-RNA molecule is released.

9
Question
  • What enzymes are responsible for the production
    of the RNA molecule?

10
Answer Helicase and RNA Polymerase
  • Helicase separates the DNA molecule by breaking
    the H-bonds between the bases.
  • RNA Polymerase moves along one of the DNA strands
    and links RNA nucleotides together.

11
1. Transcription

12
Question
  • What would be the complementary RNA strand for
    the following DNA sequence?
  • DNA 5-GCGTATG-3

13
Answer
  • DNA 5-GCGTATG-3
  • RNA 3-CGCAUAC-5

14
2. RNA Processing



Eukaryotic Cell
15
2. RNA Processing
  • Maturation of pre-RNA molecules.
  • Also occurs in the nucleus.
  • Introns spliced out by splicesome-enzyme and
    exons come together.
  • End product is a messenger RNA molecule (mRNA)
    that leaves the nucleus to the cytoplasm.

16
2. RNA Processing

17
Types of RNA
  • Three types of RNA
  • A. messenger RNA (mRNA)
  • B. transfer RNA (tRNA)
  • C. ribosomal RNA (rRNA)
  • Remember all produced in the nucleus!

18
A. Messenger RNA (mRNA)
  • Carries the information for a specific protein.
  • Made up of 500 to 1000 nucleotides long.
  • Made up of codons (sequence of three bases
    AUG - methionine).
  • Each codon, is specific for an amino acid.

19
A. Messenger RNA (mRNA)
20
B. Transfer RNA (tRNA)
  • Made up of 75 to 80 nucleotides long.
  • Picks up the appropriate amino acid floating in
    the cytoplasm (amino acid activating enzyme)
  • Transports amino acids to the mRNA.
  • Have anticodons that are complementary to mRNA
    codons.
  • Recognizes the appropriate codons on the mRNA and
    bonds to them with H-bonds.

21
B. Transfer RNA (tRNA)

22
C. Ribosomal RNA (rRNA)
  • Made up of rRNA is 100 to 3000 nucleotides long.
  • Important structural component of a ribosome.
  • Associates with proteins to form ribosomes.

23
Ribosomes
  • Large and small subunits.
  • Composed of rRNA (40) and proteins (60).
  • Both units come together and help bind the mRNA
    and tRNA.
  • Two sites for tRNA
  • a. P site (first and last tRNA will attach)
  • b. A site

24
Ribosomes
Large subunit

P Site
A Site
Small subunit
25
3. Translation



Eukaryotic Cell
26
3. Translation
  • Synthesis of proteins in the cytoplasm
  • Involves the following
  • 1. mRNA (codons)
  • 2. tRNA (anticodons)
  • 3. rRNA
  • 4. ribosomes
  • 5. amino acids

27
3. Translation
  • Three parts
  • 1. initiation start codon (AUG)
  • 2. elongation
  • 3. termination stop codon (UAG)
  • Lets make a PROTEIN!!!!.

28
mRNA Codon Translation Table
29
3. Translation
Large subunit

P Site
A Site
Small subunit
30
Initiation


anticodon
A
U
G
C
U
A
C
U
U
C
G
A
hydrogen bonds
codon
mRNA
31
Elongation
peptide bond
aa1
aa2


1-tRNA
2-tRNA
anticodon
U
A
C
G
A
U
A
U
G
C
U
A
C
U
U
C
G
A
hydrogen bonds
codon
mRNA
32
aa1
peptide bond
aa2


1-tRNA
U
A
C
(leaves)
2-tRNA
G
A
U
A
U
G
C
U
A
C
U
U
C
G
A
mRNA
Ribosomes move over one codon
33
peptide bonds
aa1
aa2
aa3
2-tRNA
3-tRNA
G
A
U
G
A
A
A
U
G
C
U
A
C
U
U
C
G
A
A
C
U
mRNA
34
peptide bonds
aa1
aa2
aa3
2-tRNA
G
A
U
(leaves)
3-tRNA
G
A
A
A
U
G
C
U
A
C
U
U
C
G
A
A
C
U
mRNA
Ribosomes move over one codon
35
peptide bonds
aa1
aa2
aa4
aa3
3-tRNA
4-tRNA
G
A
A
G
C
U
G
C
U
A
C
U
U
C
G
A
C
C
U
mRNA
36
peptide bonds
aa1
aa2
aa3
aa4
3-tRNA
G
A
A
4-tRNA
G
C
U
G
C
U
A
C
U
U
C
G
A
C
C
U
mRNA
Ribosomes move over one codon
37
aa5
aa4
Termination
aa199
aa200
primary structure of a protein
aa3
aa2
aa1
terminator or stop codon
200-tRNA
C
C
A
U
G
U
U
U
A
G
C
U
mRNA
38
End Product
  • The end products of protein synthesis is a
    primary structure of a protein.
  • A sequence of amino acid bonded together by
    peptide bonds.

39
Question
  • The anticodon UAC belongs to a tRNA that
    recognizes and binds to a particular amino acid.
  • What would be the DNA base code for this amino
    acid?

40
Answer
  • tRNA - UAC (anticodon)
  • mRNA - AUG (codon)
  • DNA - TAC

41
When things go wrong
  • Mutations changes in the DNA sequence, that may
    be passed along to future generations.
  • Point mutations a single base substitution
  • THE CAT SAW THE RAT
  • THE CAT SAW THE HAT
  • Deletion a small DNA segment is lost
  • THE CAT SAW THE RAT
  • THE ATS AWT HER AT
  • Insertion a segment of DNA is added
  • THE CAT SAW THE HAT
  • THE CAT SAW THE BHAT

42
Mutations
  • Frame-shift mutation modification of the reading
    frame after a deletion or insertion, resulting in
    all codons downstreams being different.
  • For example
  • THE RAT SAW THE CAT AND RAN
  • If you take out the R in RAT and shift the
    frames, you get
  • THE ATS AWT HEC ATA NDR AN
  • The resulting sentence (or mRNA message) is
    meaningless!

43
Mutations
  • Somatic mutations occur in body cells, or cells
    that do not lead to gametes.
  • Somatic mutations that occur in leaves, roots or
    stems are usually not passed on to future
    generations UNLESS the plant is reproduced
    asexually.
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