Lecture 6 Protein Synthesis

Front 1

Gene

Back 1

segment of DNA coding for RNA which be produced to make a polypeptide

Front 2

How many genes are in a single strand of DNA?

Back 2

it can contain 1000s

Front 3

Each gene has

Back 3

a beginning and an end

Front 4

When replication is not occurring DNA is used as a blueprint for what?

Back 4

proteins

Front 5

Genetic Code

Back 5

DNA nucleotide sequence that codes for the order of amino acids in proteins

Front 6

Codon

Back 6

triplets of nucleotides that code for a specific amino acid

Front 7

There are 20 different amino acids, but how many possible codons?

Back 7

64 ( each of the 3 nucleic bases can be rearranged)

Front 8

Does only one single codon code for a amino acid?

Back 8

No it is some what redundant and can be several codons that all code for the same amino acid

Front 9

Where do we see the genetic code other than humans?

Back 9

Everywhere, it is universal in all organisms

Front 10

What is the first step to Protein synthesis?

Back 10

Transcription

Front 11

Transcription

Back 11

DNA is transferred to RNA

Front 12

Where does transcription occur?

Back 12

In the nucleus

Front 13

What types of RNA can be transcribed form DNA?

Back 13

mRNA

rRNA

TRNA

Front 14

mRNA

Back 14

messenger RNA, carries the coded message form DNA to ribosomes in the cytoplasm

Front 15

Stages of transcription

Back 15

1. Initiation

2. Elongation

3. Termination

4. Post transcriptional modifications

Front 16

Initiation

Back 16

begins by transcription factors binding at Promoter region and ends at termination sequence

Front 17

Promoter region of DNA

Back 17

TATA box informs RNA polymerase where to begin transcription

Front 18

RNA polymerase in Transcription

Back 18

binds to promoter (TATA)
unwinds DNA
Elongates the RNA segment

Front 19

Elongation of RNA Transcription

Back 19

1. RNA nucleotides added 5'-3' by RNA Polymerase

2. RNA nucleotides form temporary H+ bonds with DNA Template

3. As DNA helix reforms RNA peels away

Front 20

Termination

Back 20

Termination sequence causes RNA polymerase to stop added nucleotides and pre RNA dissociates from DNA

Front 21

Pre mRNA modifications

Back 21

5' Cap, guanine triphosphate

3' poly tail (about 250 AA)

Introns Spliced out

Front 22

Why purpose does a 5 ' cap have?

Back 22

guanine triphosphate signals for ribosomal attachment in cytoplasm

Front 23

What purpose does the 3'poly tail have ?

Back 23

protects RNA form being degraded by nuclease

Front 24

What are introns?

Back 24

sections of RNA found in eukaryotic cells that do not code for anything and must be removed by a spliceosome (snRNPs)

Front 25

Exons

Back 25

coding regions of mRNA in eukaryotic cells

Front 26

Post transcriptional modification of rRNA

Back 26

rRNA associate with proteins to form two units a small (40s) and a large (60s) and then it enters the cytoplasm

Front 27

Post Transcriptional modifications of tRNA

Back 27

folds into the clover shape, anticodon, 5' and 3'(amino acids attach)

Front 28

What happens after the RNA strands are transcribed and modified?

Back 28

They leave the nucleus and go into the cytoplasm

where translation occurs

Front 29

Translation

Back 29

going form the mRNA nucleotide code to amino acid code

Front 30

Where does translation occur?

Back 30

Cytoplasm

Front 31

Steps of Translation

Back 31

1. Initiation

2. Elongation

3. Termination

4. modifications

Front 32

Overview of translation

Back 32

mRNA is read by ribosome (rRNA) to determine the sequence of amino acids to produce a polypeptide

Front 33

Players in Translation

Back 33

mRNA

rRNa

tRNA

Enzymes

Front 34

rRNA

Back 34

Ribosomal RNA (AKA ribosomes)

Front 35

rRNA structure

Back 35

mRNA binding site
3 tRNA binding sites(large)
1. A-site
2. P-site
3. E- Site

Front 36

A- Site of rRNA

Back 36

amino-acyl binding site

Front 37

P- Site of rRNA

Back 37

Peptidyl binding site

Front 38

E- site of rRNA

Back 38

exit site

Front 39

tRNA structure

Back 39

folded into clover shape

has Anticodon

3' end has binding site for specific the amino acid it carries

Front 40

Anticodon

Back 40

3 base sequence that is complementary to the codon on the mRNA

Front 41

Initiation of Translation

Back 41

1. mRNA binds to 40s ribosome unit

2. 1st tRNA binds to mRNA at AUG at P-site of rRNA

3. anticodon of tRNA matches codon on mRNA

4. 60s ribosome unit arrives completing the initiator complex

Front 42

Initiator complex

Back 42

mRNA

40s and 60s ribosomes

tRNA with matching anticodon at AUG

Front 43

Start codon

Back 43

AUG, codes for methionine and is later removed by aminopeptidase

Front 44

Elongation of polypeptide chain

Back 44

1. Next tRNA enters at A site of rRNA
2. Peptidyl transferase forms peptide bond between amino acid on the P site to the new one on the A site,now amino acids in A site
3. Ribosome does translocation
4. tRNA that was at A-site is now at P-site, tRNA that was at P-site now at E-site exits
5. tRNA is Charged with new amino acid
Process continues

Front 45

Translocation

Back 45

rRNA or ribosomes move down the mRNA strand

Front 46

Charging of tRNA

Back 46

amino acids that are floating freely in the cytoplasm are attached to 3'end of tRNA by amino-acyl tRNA synthetase; requires ATP

Front 47

Termination of Translation

Back 47

Occurs at the stop codon along the mRNA strand
(UAA, UAG, UGA) causing the polypeptide to be released form the ribosome by a release factor (release factor binds to A site with no amino acid)

Front 48

Polysomes

Back 48

several ribosomes can simultaneously translate the same mRNA strand to make multiple copies of the same polypeptide

Front 49

Post- Translational Modifications

Back 49

1. Start methionine is removed by aminopeptidase

2. Proteins will undergo folding or modifications

Front 50

Protein modifications

Back 50

1. Cleavage into smaller fragments or joined with other polypeptides

2. Chemical: adding carbs or lipids

3. Transport to final destination

Front 51

Mutations

Back 51

change in the sequence of bases within a gene

Front 52

Causes of Mutations

Back 52

DNA replication (Rare)

Mutagens

Front 53

Types of Mutation

Back 53

1. Point mutations

2. Frame-shift mutations

Front 54

Point Mutations

Back 54

Aka substitutions; change in a single nucleotides, due to the genetic code redundancy it may be silent or may not change the amino acid

Front 55

Frame- Shift mutation

Back 55

caused by an insertion or a deletion of a nucleotide; changes reading frame of codons, usually not functional protein results

Front 56

Are all mutations bad?

Back 56

Not always, they are the source for the rich diversity of genes; and contribute to the process of evolution by natural selection

Front 57

example of initiation of transcription

Back 57

Blood glucose high so gene is turned on in beta cells (transcription factors or enzymes bind) signalling to the gene for insulin to be transcribed

Front 58

AUG

Back 58

always start codon "August" beginning of school or Fall semester

Front 59

What happens to polypeptides?

Back 59

may go to free ribosome to make polypeptide; mitochondria, peroxisome, etc.

or may go to fixed ribosome in ER and transported to Golgi apparatus, stay in cell or leave

Front 60

Germination mutations

Back 60

gametes (all cells in fertilized egg has muatation) can be silent and show up later ;cancer

Front 61

Somatic Mutation

Back 61

specfic tissues only; skin cells (all skin cells would be different but would not affect other tissues)(mutagens, or age etc)

Front 62

Types of mutations general

Back 62

Germination
Somatic