1. Protein Synthesis: Transcription

2. Objectives What is the Central Dogma of biology?
What are the steps of transcription?

3. Recall Why do we need proteins?
Muscles, hair, nails cartilage, tendons, ligaments
Enzymes
Hemoglobin
Antibodies

4. Central Dogma How genetic information flows in a system.
Must convert the code to RNA and then to a Protein
What does dogma mean ?
established opinion, believed to be true. Code of beliefs
So how do we make proteins that are so essential ??

5. What are proteins made of?
Amino Acids are the individual building blocks
Together to make one Protein
There are 20 types of amino acids, some
There are infinite combinations of amino acids
These long chains are called polypeptide chains
Amino acids are monomers, that make up the polymer, protein
Polypeptide, because the bond holding amino acids together are peptide bonds

6. Protein Synthesis
Protein synthesis is the process in which a cell makes protein based on the message contained within its DNA.
However:
DNA is only found in the nucleus
Proteins are only made outside the nucleus – in the cytoplasm.

7. Protein Synthesis
How do the many different messages within the DNA molecule get to the many ribosomes outside the nucleus?
A molecular cousin of DNA – RNA – is used to carry these messages.

8. Ribonucleic Acids - RNA
The job of RNA (ribonucleic acid) is to carry messages from the DNA (in the nucleus) to the ribosomes (in the cytoplasm).

9. Differences between RNA and DNA
Single Stranded
Ribose sugar group
Nitrogen Base Pairs
A-U, C-G
DNA
Double-stranded
Deoxyribose sugar group
Nitrogen Base Pairs
A-T, C-G
Nucleotides are made up of
Phosphate group
sugar
Nitrogen bases DNA vs RNA
Deoxyribonucleic acid and RiboNucleic acid
hydroxy group on RNA and not DNA – extra O does not allow to form a double helix

11. Types of RNA mRNA: carries the message from the DNA to the cytoplasm
tRNA: transports amino acids to the mRNA to make the protein
rRNA: make up the ribosomes, which help make the protein
mRNA – carries code into cytoplasm where translation will occur
tRNA – reads the code and carries the amino acid to be in protein
rRNA- found on the RNA itself. Helps make the peptide

12. Protein Synthesis Process
Occurs in TWO steps:
Transcription – the genetic information from a strand of DNA is copied into a strand of mRNA
Translation

13. Steps of Transcription
1. DNA unwinds
Enzymes help split apart base pairs to open the DNA double helix.
Transcription complex: RNA polymerase and proteins
Uses one strand as a template
2. Bases line up
Free nucleotides in the cell find their complementary base pairs on the DNA template strand
What will be different??

15. Steps of Transcription
3. RNA formed
The growing RNA strand hands greely as it is transcribed.
DNA strand must close back up
4. The completed RNA strand separates from the DNA template

16. Steps of Transcription

17. Try It! What will the RNA Strand be?
TACGCATGGCATGCAA

18. Try It! What will the RNA Strand be?
TACGCATGGCATGCA
AUGCGUACCGUACGU

19. Think, Pair, Share 1. What is the purpose of Protein Synthesis?
2. List 2 differences between DNA and RNA
3. Where in the cell does the process of transcription occur?
4. What enzyme completes the process of transcription?
5. What molecule is produced from transcription?
6. Where does this molecule go after it is made?

20. Introns and Exons The DNA that is copied contains both…
Introns: sequences of nucleotides not involved in coding for proteins.
AND
Exons: DNA sequences that code for proteins

21. By the end of the day today you should:
Objectives
By the end of the day today you should:
Know the steps of translation
Identify the differences in transcription and translation

22. Translation
Now that the mRNA has been made, the next step is for its’ message to be made into a protein
Translation: the mRNA, with the help of the ribosome, forms a chain of amino acids (eventually forming a protein) based on the information contained on the mRNA.
Occurs in the cytoplasm on the ribosome

24. Proteins Proteins are made of amino acids
20 different amino acids total
Adult humans can only make 12 out of the 24 amino acids
How do we attain the other 8 amino acids?
Some amino acids can be converted to each other, but not created from scratch. Some amino acids can be synthesized, but not rapidly enough to meet all our metabolic needs. And children can’t synthesize some of the amino acids that adults can.

25. Translation One Problem
There are 20 amino acids
There are 4 RNA bases
How can just four nucleotides—A, U, C, G—be translated into so many different amino acids?

26. Language of RNA
Just like the alphabet, 26 letters can make more than 26 words
Letters of RNA are put together in different ways.
Codon: three nucleotide sequence which codes for the insertion of a unique amino acid
Language of the genetic code
Multiple codons for the same amino acid
Anticodon: on one end of tRNA complementary to a specific mRNA codon
tRNA molecules carry different amino acids

28. Genetic Code
Start Codon – signals the start of translation (AUG- Methionine)
Stop codon – signal the end of the amino acid chain (3 total)

30. Translation
Before translation begins, a ribosome will be assembled from two ribosomal subunits (large and small). The ribosome contains three attachment sites for tRNA molecules.
On the large subunit: E site, A site and P site
On the small subunit: mRNA joins

31. Step 1: mRNA attaches to the small ribosomal unit
Step 1: mRNA attaches to the small ribosomal unit. The large subunit attaches to the small subunit. The first codon is aligned at the P site.

32. Step 2: A tRNA carrying the amino acid methionine attaches to the start codon, AUG, on the mRNA. This happens at the P site on the large ribosome

33. Step 3: Attachment of the first amino acid carrying tRNA to A binding site.

34. Step 4: The ribosome forms a peptide bond between the two amino acids and breaks the bond between the first tRNA and its amino acid.

35. Step 5: The ribosome pulls the mRNA the length of one codon
Step 5: The ribosome pulls the mRNA the length of one codon. The tRNA and polypeptide chain move to the P site. The first tRNA is shifted to the E site.

36. Step 6: tRNA is ejected from the E binding site and returns to the cytoplasm. The A site is now open for another tRNA.

37. Step 7: This process continues to translate the mRNA strand until it reaches a stop codon. The protein is released and the large and small ribosome disassemble.

38. st. olaf transcription animation
whfreeman animation

39. Mutations

40. Objectives
What are different types of mutations that can occur during protein synthesis?

41. Mutations Mutations are changes in the DNA sequence
DNA damage from environmental agents:
UV Light
Chemicals
Mistakes that occur when DNA is copied before cell division
Point Mutation: a change in a single base pair of a gene

42. No Mutation:
DNA Sequence: TACAAG
mRNA Sequence: AUGUUC
Amino Acid Chain: Met – Phen
Point Mutation:
DNA Sequence: TACATG
mRNA Sequence: AUGUAC
Amino Acid Chain: Met – Tyr

43. Other Types of Mutations
Substitution
change a codon to one that encodes the same amino acid and causes no change in the protein produced.
change a codon to one that encodes a different amino acid and cause a small change in the protein produced

44. Other Types of Mutations
Insertions
mutations in which extra base pairs are inserted into a new place in the DNA

45. Other Types of Mutations
Deletion
mutations in which a section of DNA is lost, or deleted.