1. Protein Synthesis

2. Protein Synthesis Overview
The information in DNA is used to make proteins. These proteins are used for a variety of purposes within the body. (do you remember why our body needs protein?)

3. Introduction to Protein Synthesis

4. Protein Synthesis Overview
However there is a problem. The DNA never leaves the nucleus. But the ribosomes, (remember? they make proteins) are in the cytoplasm. How can the information get from the nucleus to the ribosomes in the cytoplasm?

5. Protein Synthesis Overview
The solution is that the cell makes a temporary copy of the DNA. The temporary copy is called RNA.

6. RNA Page 3 The letters RNA stand for: ribonucleic acid
Like DNA, RNA is made up of nucleotides
The structure of an RNA nucleotide:
1. phosphate (acid)
2. ribose (sugar)
3. nitrogenous base

7. RNA Page 3 What bases are present in RNA? Adenine (A)
Uracil (U) instead of thymine
Guanine (G)
Cytosine (C )
*All RNA is single stranded**
Page 3

8. 1. Messenger RNA The three main types of RNA
Acts as a messenger, carries a copy of the directions from the DNA in the nucleus to the ribosome in the cytoplasm

9. The three main types of RNA
2. Ribosomal RNA
3. Transfer RNA
part of the ribosome, the ribosome is made up of proteins plus rRNA.
Amino Acid
transfers an amino acid to the ribosome
Anti-codon

10. tRNA
Ribosome

11. Comparing DNA and RNA
DNA
RNA
similarities
differences
differences

12. Comparing DNA and RNA
DNA
RNA
similarities
differences
differences

13. Protein Synthesis Overview

14. Transcription Summary

15. RNA Polymerase makes mRNA RNA Polymerase breaks H-bonds
Deoxy-ribose P
Thymine
Cytosine
Adenine
Ribose P
Uracil
Ribose P
Guanine
Uracil
Adenine
Adenine
Deoxy-ribose P
Guanine
Thymine
---H---
Transcription
Ribose P
Guanine
RNA Polymerase makes mRNA
Strands move apart
mRNA exits nucleus
RNA Polymerase breaks H-bonds
DNA re-coils
---H---
Ribose P
Adenine
---H--- P

16. Transcription
Transcription is the first step in protein synthesis. The purpose is to make RNA, a copy of the information in DNA. This process occurs in the nucleus.
To get started you need:
DNA
Free RNA nucleotides
RNA polymerase

17. Step 1: Initiation RNA polymerase attaches to a promoter region of DNA
Draw This image
Step 1: Initiation
RNA polymerase attaches to a promoter region of DNA
RNA Polymerase

18. Draw This image
Step 2: Elongation
RNA polymerase opens the DNA helix. It makes a little bubble. One strand will act as a template.
RNA polymerase moves down the DNA molecule attaching complementary RNA nucleotides as it goes.
Everything is the same as DNA replication except:
The DNA A pairs with RNA U
Template Strand
Complimentary Strand

19. Step 3: Termination
Draw This image
Transcription stops when RNA polymerase reaches the terminator region of DNA.
RNA Polymerase
Stays in the nucleus

20. mRNA editing
Step 1
A cap and a tail are added to the ends of the mRNA

21. mRNA editing
The DNA and RNA contain portions called Exons and Introns.
After the RNA is made:
the Introns are removed
the Exons are “expressed”, they are used to make proteins.
The RNA leaves the nucleus and travels out to the cytoplasm.

22. RNA Splicing

23. Codons
A codon is . . .
Any three consecutive nucleotides.
Animation

24. Reading Frames

25. A brief detour DO bacteria have DNA?
Do bacteria do DNA replication? Where?
Do bacteria do transcription and translation? Where?

26. Protein Synthesis Overview
Animation

27. About proteins
Short review

28. Protein Structure Review
What are the monomers of proteins?
Amino Acids
How many different amino acids are there? 20
What are the three parts of the amino acid?
What are the four levels of organization?

29. Translation
Quick view

30. Translation Mechanism
MET
This process continues until a stop codon is reached, at which point the mRNA strand, tRNA units, and rRNA subunits all are released.
MET
ISO
PRO A U G C
tRNA
U A U
tRNA
U A C
tRNA
U A C
tRNA
U A U
tRNA
G G G
Start Codon (Methionine)
Large Ribosomal Subunit (rRNA)
E Site
A Site
P Site
mRNA A U G C
Small Ribosomal Subunit (rRNA)

31. Translation Location: In the cytoplasm Purpose: to make proteins
What we need to get started:
mRNA
small ribosomal subunit
large ribosomal subunit
charged tRNA

32. Translation - Initiation
Image 1 of 4
tRNA
mRNA
Draw This image
Box #1
Ribosome
The small ribosomal subunit binds to the mRNA cap and moves down the mRNA until it reaches the start codon (AUG).
Next the first tRNA (with the anti-codon UAC) and the large ribosomal subunit will bind to the small ribosomal subunit.

33. Translation - Elongation
Image 2 of 4
Peptide bond
tRNA
Met= methionine
met
mRNA
Draw This image
Box #2
Ribosome
A new tRNA molecule attaches to the ribosome in the A site. This tRNA will pair with the next codon of mRNA.
The ribosome will form a peptide bond between the amino acids attached to the first two tRNAs.

34. Translation - Elongation
Image 3 of 4
To be recharged
tRNA
mRNA
Draw This image
Box #3
Ribosome
Once the bond is formed the ribosome will move over causing the tRNA to exit the ribosome.

35. Translation - Termination
Image 4 of 4
AGC
Draw This image
Box #4
The ribosome will continue to move down the mRNA, adding amino acids to the growing string of amino acids until it reaches the stop codon.
No tRNA bonds to the ribosome and translation is over!
The complex will come apart.

36. Prokaryotic Eukaryotic

37. Post-translation . . .
The new protein is released. The string of amino acids fold-up into the shape of the protein.

38. How do cells control protein expression?
Transcription can be turned on and off using feedback mechanisms.
Control quantity of proteins by producing different numbers of mRNAs

39. Summary
The goal of translation is transfer information from RNA to Protein
Translation occurs in the cytoplasm of the cell.
Animation

40. From DNA to Protein

41. Reading the Code
mRNA
tRNA
Amino
acid

42. Codon Bingo

43. Alternate codon tables

44. Mutations
Despite its speed (50–500 pairs per second), replication is very accurate. It only makes approximately one mistake in every billion nucleotide pairs. Mistakes in the DNA sequences are called mutations. DNA polymerases and DNA ligase proofread the new daughter strands and fix these mistakes..
Replication assures that new cells will carry the same genetic information as each other and as the parental cell.

45. Mutations fall into two basic categories:
Types of Mutations
Mutations fall into two basic categories:
Gene mutations: changes in the nucleotide sequence that affects the gene
Chromosomal mutations: changes to a chromosome that affect many genes
Tell students: Mutations come in many different forms. The flower shown on the previous slide and the lion shown on this one are just two of countless examples.
Explain to them that all mutations fall into two basic categories.
Click to reveal each category.
Point out that a genetic condition called leucism leaves the lion shown without pigments in its hair, skin, and eyes.
Ask: Which type of mutation is likely to be more harmful?
Answer: A chromosomal mutation is likely to be more harmful because many genes are found on one chromosome.

46. Causes of Mutations Mistakes in base paring during DNA Replication
Cause of many genetic disorders
Chemicals: like tobacco
Can lead to cancer because it changes the genes that regulate mitosis
Radiation: including UV (sun) and X-ray

47. Gene Mutations: Point Mutations
A point mutation is a change in a single nucleotide.
There are three types of point mutations:
Tell students: Changes in a single nucleotide can affect the amino acid sequence of proteins.
Point mutations include three types: substitutions, insertions, and deletions.
Click to highlight these types.
Tell students: You will learn more about each mutation in the coming slides.
Point mutations generally occur during replication.
If a gene in one cell is altered, the alteration can be passed on to every cell that develops from the original one.
Ask: What can a mutation do to the outcome of transcription and translation?
Answer: Mutations change the code. This changes the mRNA code. This changes the amino acids in the protein. This changes the protein structure. This can affect the protein function.

48. Point Mutations: Substitutions
Point where one nitrogen base is substituted for another
Sickle Cell Anemia: substitute A for T
Explain to students that substitutions usually affect no more than a single amino acid, and sometimes they have no effect at all.
Ask: In the example shown, before the mutation, what is the second codon and what amino acid does it specify?
Answer: The second codon is CGU and it specifies arginine.
Click to highlight the arginine information.
Point out that when a single nucleotide is replaced, in this case thymine replacing cytosine, the codon is changed.
Ask: In the example shown, what change occurred in the codon?
Answer: The second codon is now CAU, which specifies histidine.
Click to highlight the histidine information.
Point out to students that not all mutations result in a change to the amino acid.
For example, if a mutation changed one codon of mRNA from CCC to CCA, the codon would still specify the amino acid proline.
Ask a volunteer to point out CCC and Proline.
Click to highlight the CCC.
Then ask the same volunteer to point out why CCA would result in the same amino acid.

49. Point Mutations: Insertions and Deletions
Insertion mutation: when a single extra base is added into the code
Deletion mutation: when a single base is removed from the code
Point out to students that the significance of either insertions or deletions can be dramatic.
Ask: Why do you think that an insertion or a deletion could have a dramatic effect?
Answer: Because the genetic code is read three bases at a time. If a nucleotide is added or deleted, the entire reading frame is shifted. Consequently, every amino acid after the mutation will likely be altered.
Tell students: Insertions and deletions are also called frameshift mutations for this reason.
These mutations can alter a protein so much that it is unable to perform its normal functions.
Activity: Write the following sentence on the board without spaces: Theboysawthetandogrun.
Tell students: Read the sentence three letters at a time.
Add an “x” after the first “The” and give the students the same directions to read the sentence.
Discuss how this example relates to frameshift mutations.

50. Frameshift Mutation Caused by insertions or deletions
Called a frameshift mutation because they shift the “reading frame”
Changes every amino acid after the mutation site to change such that the protein is unable to perform its normal functions.

51. Nonsense mutation Base substitution that results in a stop codon
Creates a shorter and probably non-functional protein.

52. Silent Mutation
Mutation that does not result in an amino acid change.

53. Effects of Mutations
Mutations can harm, help, or have no effect on an organism.
Most mutations have no affect.
Some mutations arise from mutagens—which are mutation causing chemicals or physical agents in the environment.
Chemical mutagens: certain pesticides, tobacco smoke, environmental pollutants
Physical mutagens: certain types of radiation such UV and X-rays.
Explain how the effects of mutations can be minimal, beneficial, or disastrous to an organism.
Explain to students that chemical mutagens include certain pesticides, a few natural plant alkaloids, tobacco smoke, and environmental pollutants.
Physical mutagens include some forms of electromagnetic radiation, such as X-rays and ultraviolet light.
Tell students: If these agents interact with DNA, they can produce mutations at high rates.
Cells can sometimes repair the damage, but when they cannot, the DNA base sequence changes permanently.
Ask: What would be the effect of a compound that interferes with base pairing?
Answer: It would increase the error rate of DNA replication.
Point out that other compounds can actually weaken the DNA strand, causing breaks and inversions that produce chromosomal mutations.

54. 6. Effects of Mutations: Harmful
Some of the most harmful mutations are those that dramatically change protein structure or gene activity.
Can cause cancer or inherited disorders such as sickle cell.
Example: Sickle cell disease affects the shape of red blood cells.
Tell students: Some of the most harmful mutations are those that dramatically change protein structure or gene activity.
The defective proteins produced by these mutations can disrupt normal biological activities and result in genetic disorders.
Some cancers, for example, are the product of mutations that cause the uncontrolled growth of cells.
Point out that sickle cell disease is a disorder associated with changes in the shape of red blood cells, as shown in this image.
Sickle cells are crescent- and star-shaped.
Click to highlight a normal red blood cell versus a sickle cell.
Explain that this disease is caused by a substitution mutation in one of the polypeptides found in hemoglobin, the blood’s principal oxygen-carrying protein. Among the symptoms of the disease are anemia, severe pain, frequent infections, and stunted growth.
Sickle cell
Normal red blood cell

55. 6. Effects of Mutations: Beneficial
Mutations often produce proteins with new or altered functions that can be useful to organisms as they adapt to different or changing environments.
Mosquitos have become resistant to pesticides
Humans: increase resistance to HIV, ability to drink milk, skin-color
Plant & Animal Breeding: use desired mutations to breed new and/or improved species.
Explain that some of the variation produced by mutations can be highly advantageous to an organism or species.
Tell students: Mutations have helped many insects become resistant to chemical pesticides and have enabled microorganisms to adapt to new chemicals in the environment.
Also explain that plant and animal breeders often make use of “good” mutations. For example, when a complete set of chromosomes fails to separate during meiosis, the gametes that result may produce triploid (3N) or tetraploid (4N) organisms. The condition in which an organism has extra sets of chromosomes is called polyploidy.
Ask: Based on this information, why might plant breeders want to encourage these “good” mutations?
Answer: Changes to the ploidy number of citrus plants can affect the size and strength of the trees as well as the quality and seediness of their fruit. Polyploid plants are often larger and stronger than diploid plants. Important crop plants—including bananas and limes—have been produced this way.