1. PROTEIN SYNTHESIS Chapter 9 Bio 2A

2. What are some examples of proteins?

3. Why are Proteins Important?
Structural Proteins
Keratin = skin and Myosin = muscle
Enzymes – speed up reactions
Hemoglobin-transports oxygen on RBC’s
Hormones – Insulin keeps blood sugar in check
Receptor proteins-allow things to enter and leave cells

4. Keratin

5. Myosin

7. Insulin Hormone

8. Enzymes

9. Receptor Proteins

10. DNA DNA contains genes, sequences of nucleotide bases
These Genes code for polypeptides (proteins)
Proteins are used to build cells and do much of the work inside cells

11. Genes & Proteins
Proteins are made of amino acids linked together by peptide bonds
20 different amino acids exist

12. Polypeptides
Amino acid chains are called proteins or polypeptides…all the same thing.

13. DNA Begins the Process DNA is found inside the nucleus
Proteins are made in the cytoplasm of cells at organelles called ribosomes
Ribosomes may be free in the cytoplasm or attached to the surface of rough ER

14. Why can’t DNA leave the nucleus?
Degradation, damage, distortion
Inefficient protein production…each protein would have to be made one at a time since there is only one DNA molecule.
It would have to have a nucleus reentry strategy

15. Starting with DNA
DNA ‘s code must be copied and taken to the cytoplasm
In the cytoplasm, this code must be read so amino acids can be assembled in the right order to make certain polypeptides (proteins)
This process is called PROTEIN SYNTHESIS

16. The Central Dogma of molecular genetics
Genes found within a DNA sequence are transcribed into messenger RNA. Messenger RNA exits the nucleus and is translated into protein by ribosomes in the cytoplasm

17. DNA  mRNA  Protein Eukaryotic Cell DNA Pre-mRNA mRNA Ribosome
Nuclear
membrane
Transcription
RNA Processing
Translation
DNA
Pre-mRNA
mRNA
Ribosome
Protein
Eukaryotic Cell

18. RNA and DNA
RNA has a sugar ribose
DNA has a sugar deoxyribose

19. RNA and DNA RNA contains the base uracil (U) DNA has thymine (T)
RNA molecule is single-stranded
DNA is double-stranded
RNA
DNA

20. Structure of RNA

21. Three Types of RNA .
Messenger RNA (mRNA) –copies DNA’s code & carries the genetic information to the ribosomes
Ribosomal RNA (rRNA) -along with protein, makes up the ribosomes
Transfer RNA (tRNA) -transfers amino acids to the ribosomes where proteins are synthesized

22. Messenger RNA Long Straight chain of Nucleotides Made in the Nucleus
Contains the Nitrogen Bases A, G, C, U ( no T )
Copies DNA & leaves through nuclear pores

23. Messenger RNA (mRNA)
Ribosomes make proteins using mRNA as the template.
Ribosomes read mRNA in a sequence of 3 bases at a time. This 3 base sequence is called a codon
AUG – methionine or start codon
UAA, UAG, or UGA – stop codons

24. Ribosomal RNA (rRNA) – RIBOSOMES
Made inside the nucleus of a cell
It’s made of rRNA and protein.
Can adhere to RER or float freely in cytoplasm
Site of protein synthesis

25. The Genetic Code
Each codon (three base sequence on mRNA) codes for a specific amino acid.
Scientists hae figured out which codon codes for which amino acid
Example: AUG codes for Methionine

26. Practice
GGG?
UCA?
CAU?
GCA?
AAA?

28. Transfer RNA (tRNA) Clover-leaf shape
amino acid
attachment site U A C
anticodon
Clover-leaf shape
Single stranded molecule with attachment site at one end for an amino acid
Opposite end has three nucleotide bases called the anticodon

30. Codons and Anticodons
The 3 bases of an anticodon are complementary to the 3 bases of a codon
Example: Codon ACU
Anticodon UGA
UGA
ACU

31. Some Characteristics of Protein Synthesis
All RNA is built in the Nucleus
mRNA is assembled from DNA in the nucleus
rRNA and tRNA travel and work outside of the nucleus
rRNA + protein = Ribosomes
tRNA = has the anticodon at one end and the proper amino acid at the other
mRNA travels out of nucleus to a ribosome to start making proteins

32. Step 1 - Transcription
The process of copying the sequence of one strand of DNA, the template strand
mRNA copies the template strand
Requires the enzyme RNA Polymerase

33. What would be the complementary RNA strand for the following DNA sequence?
DNA 5’-GCGTATG-3’

34. RNA Polymerase

35. http://vcell. ndsu. nodak. edu/animations/transcription/movie-flash

36. Transcription
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
Promoters are regions on DNA that show where RNA Polymerase must bind to begin the Transcription of RNA
Regions promoters start is called the TATA box
Specific base sequences act as signals to stop
Called the termination signal

37. Result of Transcription
New Transcript
Tail
CAP

38. mRNA Processing & Editing
After the DNA is transcribed into RNA, editing must be done to the nucleotide chain to make the RNA functional
Introns, non-functional segments of RNA are snipped out of the chain
Exons, segments of RNA that are expressed into proteins, are then rejoined by the enzyme ligase
A guanine triphosphate cap is added to the 5” end of the newly copied mRNA
A poly A tail is added to the 3’ end of the RNA
The newly processed mRNA can then leave the nucleus

39. mRNA Transcript
mRNA leaves the nucleus through its pores and goes to the ribosomes

40. Messenger RNA (mRNA) Primary structure of a protein A U G C aa1 aa2
start
codon
codon 2
codon 3
codon 4
codon 5
codon 6
codon 7
codon 1
methionine
glycine
serine
isoleucine
alanine
stop
codon
protein
Primary structure of a protein
aa1
aa2
aa3
aa4
aa5
aa6
peptide bonds 40 40

41. Translation
Translation is the process of decoding the mRNA into a protein
Ribosomes read mRNA three bases or 1 codon at a time and construct the proteins

42. Transcription Translation
Transcription occurs when DNA acts as a template for mRNA synthesis. Translation occurs when the sequence of the mRNA codons determines the sequence of amino acids in a protein.
Translation

43. Ribosomes Made of a large and small subunits
Composed of rRNA (40%) and proteins (60%)
Have two sites for tRNA attachment --- P and A
P= where peptide bond is made
A= where new amino acid is delivered by the tRNA

44. Ribosomes
Large
subunit P
Site A
Site
mRNA A U G C
Small subunit

45. Step 1- Initiation
mRNA transcript start codon AUG attaches to the small ribosomal subunit
large subunit attaches to the small ribosomal subunit
mRNA transcript

46. Step 2 - Elongation
As ribosome moves, two tRNA with their amino acids move into site A and P of the ribosome
Peptide bonds join the amino acids

47. Initiation G aa2 A U U A C aa1 A U G C U A C U U C G A codon 2-tRNA
anticodon A U G C U A C U U C G A
hydrogen
bonds
codon
mRNA

48. Elongation G A aa3 peptide bond aa1 aa2 U A C G A U A U G C U A C U U
3-tRNA G A
aa3
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

49. Ribosomes move over one codon
aa1
peptide bond
3-tRNA G A
aa3
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

50. peptide bonds G C U aa4 aa1 aa2 aa3 G A U G A A A U G C U A C U U C G
4-tRNA G C U
aa4
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

51. Ribosomes move over one codon
peptide bonds
4-tRNA G C U
aa4
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

52. peptide bonds U G A aa5 aa1 aa2 aa4 aa3 G A A G C U G C U A C U U C G
5-tRNA
aa5
aa1
aa2
aa4
aa3
3-tRNA
4-tRNA G A A G C U G C U A C U U C G A A C U
mRNA

53. Ribosomes move over one codon
peptide bonds U G A
5-tRNA
aa5
aa1
aa2
aa3
aa4
3-tRNA G A A
4-tRNA G C U G C U A C U U C G A A C U
mRNA
Ribosomes move over one codon

54. Termination aa5 aa4 aa3 primary structure of a protein aa2 aa1 A C U C
terminator
or stop
codon
200-tRNA A C U C A U G U U U A G
mRNA

55. Step 3- Termination
Once the ribosome reaches the stop codon on the mRNA, the protein is complete.
The protein detaches, is modified and will be transported to where it works in the cell.

56. End Product –The Protein!
The end products of protein synthesis is a primary structure of a protein
A sequence of amino acid bonded together by peptide bonds
aa1
aa2
aa3
aa4
aa5
aa200
aa199

57. Transport & Modification of Proteins
Protein must be modified –folded
Ex: Pepsin and Trypsin
Protein must be transported to where it will function.
Ex: outside of cell if hormone, to cell membrane if receptor, etc.
Faulty proteins (with errors) are broken down by proteosomes
Normal proteins will also be destroyed
Normal proteins have a life span
Ex: protein with Phe at end only survive a few minutes

59. Translation Errors
If the whole reading frame is shifted by a few nucleotides – Frameshift mutations
Ex: Insertion – nucleotide has been inserted on mRNA strand
Ex: Deletion – nucleotide has been deleted from mRNA strand

61. Point Mutations Involve the change in ONE nucleotide
Example: Substitution – when one base is substituted for another. May or may not affect protein.

63. Viruses Not made of cells, but replicate and divide
Consist of a Protein coat & a little genetic material
Contain DNA as genetic material or some contain RNA as genetic material
Some contain enzymes
Some contain membrane envelope – still not made of cells
Ex: Bacteriophage, HIV, Influenza

67. Viral Replication Same as for cells Two Patterns:
1. Lytic – the host (organism the virus is infecting) cells’ enzymes replicate the viral DNA. New viruses are made and the cell breaks open & releases them to infect new cells
2. Lysogenic- The Viral DNA inserts into cellular DNA & is copied when the cell replicates. Few or no new viruses are made unless a lytic cycle of replication occurs.

72. Impact of Viruses Live at the expense of the host
Replicate & evolve quickly
Can lie hidden or dormant
Viruses do not metabolize-antibiotics are useless against them.
Viruses can infect animals and plants
Reverse transcriptase- a viral enzyme that makes a DNA copy of the viral RNA. The viral DNA then directs production of new virus particles (HIV) by incorporating itself into the hosts DNA.

73. Retrovirus…like HIV
Retroviruses - employ the enzyme reverse transcriptase to produce DNA from the viral RNA. The newly produced DNA enters the nucleus and begins the process of viral replication