Chapter 12 Protein 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 RNA 1.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  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 ribosome 2.tRNA carries a specific AA to ribosome (anticodon on tRNA base-pairs with codon on mRNA) * At P site 3’ 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 synthesis b. 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 bonds f. Peptide transferase  ribosomal enzyme, which forms peptide bonds between amino acids in specific tRNA g. Activating enzymes  20 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 cytoplasm b. 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 cytoplasm d. May attach to several ribosomes (polysome) e. Exists as a short single-stranded molecule f. Processing occurs in nucleus (cut/splice-cap/tail)

Polysomes

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 RNA 2. tRNA (transfer RNA) a. Found only in the cytoplasm b. Specific amino acid attached to one end of tRNA c. 3 letter ANTICODON found at other end of tRNA d. Anticodon of tRNA will match codes of mRNA e. Brings specific amino acids into position at ribosome f. Exists as a single strand cloverleaf g. 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 RNA 3. 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 protein e. 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 code 3. 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: Substitution OR occasionally may cause detrimental effects  sickle call anemia

Cont. Mutations B. Chromosomal Mutations: chromosome rearrangements/ aberrations 1. Deletion  pieces of, or whole chromosome missing 2. Inversion  piece of chromosome breaks off and reattaches upside down 3. Duplication  extra piece of, or whole extra chromosome 4. 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 rays 2. Gamma rays uncontrolled doses 3. X-rays cause formation of ions 4. Chemicals w/in a cell Ions may interfere with: a. Normal pairing of one base with another b. 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?

Operon a.Operon  a group of genes that operate together b.Promoter  RNA polymerase binding site c.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