Chapter 12Protein Synthesis

Central Dogma: DNA RNA Protein(the flow of genetic information)

A. Gene • Segment of a DNA

molecule, which codes for specific messenger RNA (mRNA) molecule and controls a specific trait

• mRNA protein (enzyme which produces a trait)

B. DNA• Nucleic acid molecule• Controls cell activities

(cytoplasm) by determining the types of proteins (enzymes), a cell synthesizes

• Genes “make a specific protein”

2 Processes Essential to Protein Synthesis

1. Transcription – “Making a blueprint”– Synthesis of

messenger RNA from a segment of DNA (gene)

– Occurs in the nucleus– Controlled by RNA

polymerase

RNA Processing: pre-mRNA mature RNA1. RNA splicing introns removed and exons joined

together (NOW: mRNA is a continuous coding sequence)a. INTRONS- non-coding segments of nucleic acids (lie b/t exons)b. EXONS- coding segments of DNA (will be translated into AA during translation)

2. 5’ cap added to 5’ end of mRNA addition of modified form of guanine nucleotide

3. Poly-A tail added 3’ end of mRNA 50-250 A nucleotides

RNA Processing

RNA Splicing

Cont. 2 Processes Essential to Protein Synthesis

2. Translation– “Reading the blueprint” – Process at the ribosome where by genetic code

is made into a specific protein– Involves mRNA ,the tRNAs and rRNAs

(Write this Down in Notes:Steps in Translation

1. mRNA attaches to ribosome2. tRNA carries a specific AA to ribosome

(anticodon on tRNA base-pairs with codon on mRNA)* At P site3’ UAC 5’ tRNA 5’ AUG 3’ mRNA (*start codon)

3. The next tRNA enters A site and peptide bond forms (via peptide transferase) with that AA and the growing polypeptide chain- tRNA at P site leave via E site

4. Protein synthesis continues on until stop codon is read

5. After translation has ended, polypeptide is released

Steps in Translation

a. Ribosomes “factory” for protein synthesisb. mRNA “blueprint” for protein (codon)c. tRNA carry a specific a amino acid (anticodon)d. Amino Acids 20 different types (raw materials)e. ATP energy to form peptide bondsf. Peptide transferase ribosomal enzyme, which forms peptide bonds between amino acids in specific tRNA g. Activating enzymes20 different type of enzymes which link the appropriate amino acid to specific tRNA

Translation

Cont. 2 Processes Essential to Protein Synthesis

• Genes in the nucleus control enzymes and other cell proteins

• Enzyme determines the cell type and all its chemical reactions

Translation

3 Kinds of RNA

• All RNA’s are made (transcribed) from DNA templates in nucleus

1. mRNA (messenger RNA) (RNA processing occurs before they leave the nucleus)a. Found in both nucleus and cytoplasmb. Transcribes (copies) DNA codes into mRNA codes (CODONS- triplets/ 64 total that codes for 20 AA)c. Leaves the nucleus and carries the message to the ribosomes out into the cytoplasmd. May attach to several ribosomes (polysome) e. Exists as a short single-stranded moleculef. Processing occurs in nucleus (cut/splice-cap/tail)

Polysomes

The Genetic Code

The Genetic Code

Questions?

1. How many codons would it take to code 5 amino acids?

2. How many nucleotides would it take to code 5 amino acids?

Cont. 3 Kinds of RNA2. tRNA (transfer RNA)

a. Found only in the cytoplasmb. Specific amino acid attached to one end of

tRNAc. 3 letter ANTICODON found at other end of

tRNAd. Anticodon of tRNA will match codes of

mRNAe. Brings specific amino acids into position at

ribosomef. Exists as a single strand cloverleafg. Processing occurs in cytoplasm (charging

needs ATP, activating enzymes specific amino acid)

***NOTE: mRNA & tRNA have

similar structure, but have different functions

Cont. 3 Kinds of RNA3. rRNA (ribosomal RNA)

a. Found only making up structure of ribosomes

b. Is the largest of all RNA molecules

c. mRNA will attach to rRNA of ribosome and begin process of building protein

d. Composed of RNA and proteine. Comes in 2 pieces 50s (larger)

and 30s (small)f. Processing occurs in the

nucleolus

Overview of Protein Synthesis

Chapter 12: Mutations

Mutations changes in the DNA code due to:A. Point mutations: changes in the gene such as:

1. Substitution of one base to another - May have NO EFFECT on encoded protein 2. Insertion addition of an extra base in the code3. Deletion removal of a base from the sequence

*** #2 and #3 disastrous effect on resulting protein due to changes in reading frame

Point Mutation: Substitution

*** May have NO EFFECT on encoded protein!

Point Mutation: SubstitutionOR occasionally may cause detrimental effects sickle call anemia

Cont. MutationsB. Chromosomal Mutations: chromosome

rearrangements/ aberrations1. Deletion pieces of, or whole chromosome

missing2. Inversion piece of chromosome breaks off and

reattaches upside down3. Duplication extra piece of, or whole extra

chromosome4. Translocation piece of chromosome breaks off

and reattaches to nonhomologous chromosome

Mutagenic Agents any substance/ factor which causes either gene (point) or chromosomal mutations

1. Ultraviolet rays2. Gamma rays uncontrolled doses 3. X-rays cause formation of ions4. Chemicals w/in a cell

• Ions may interfere with:a. Normal pairing of one base with anotherb. Causes 2 bases that ordinarily do not combine, to form a pair ex) thymine may pair with guanine

• How would this affect DNA in cell replication? In protein synthesis?

Operona. Operon a group of genes

that operate togetherb. Promoter RNA polymerase

binding sitec. Operator (O) a regulatory

region where repressor binds to

d. Repressor enzyme that binds to O region/ turns operon “off” by preventing the transcription of genes

e. Regulatory gene synthesizes repressors (action of this protein determines whether genes are turned on/ off)

lac operon- w/o presence of lactose

In the absence of lactose, repressor switches off the operon by binding to the operator.

lac operon- w/ presence of lactose

• Inducible operon- usually turned off but can be INDUCED when lactose interacts w/ repressor protein• Repressor releases itself from operator- transcription starts!• Inducer- inactivates repressor (lactose)

trp operon• REPRESSIBLE OPERON- usually on, but can be inhibited (repressed) when tryptophan (trp) binds to repressor- Repressor binds to operator- transcription stops!- Corepressor- small mol (trp) that cooperates w/ repressor to switch off operon