1. Ribosomes and Protein Synthesis (Ch 13.2)

2. The genetic code Converting DNA to protein is a two step process
Transcription
Translation
Protein
Long chains of amino acids called polypeptide chains (macromolecule)
20 different amino acids can make polypeptide chains
Configuration of amino acids = properties of the protein (shape, function, etc.)
Genetic code: the language composed of the four bases in RNA (adenine, cytosine, guanine, uracil)
The genetic code is read three bases (letters)at a time – Each protein in three bases long (word) – each code corresponds to a specific protein
Codon: three consecutive bases (word) that specifies a single amino acid

3. Reading Codons Combinations
How many combinations can we have from 4 bases?
Amino Acids
One or many codons can specify an amino acids
Example: UUA / UUG / CUU / CUC / CUA / cug = leucine
Example: UGG = tryptophan
You have to use a genetic code table to understand the polypeptide chain that is being made (all the amino acids forming together)
Start /Stop codons
Polypeptide chains need to be told when to start or stop
Example: AUG = start codon

4. Translation Dna  Protein
Transcription: mrna copying the dna strand to leave the nucleus
Translation: mrna is translated into protein using rrna in ribosomes and trna
Ribosomes
Made up of rRna
Ribosomes use the codons in mrna to assemble amino acids and create polypeptide chains
Trna had an anticodon that base pairs with each codon  codes for an amino acid
Amino acids = polypeptide chains = proteins

5. Steps in Translation Step 1
A ribosomes attaches to an mrna strand in the cytoplasm
Codons pass through the ribosome  trna places anticodons on the codons
Anticodons: complementary code or base pair to the mrna codon
Trna anticodons code for amino acids that will continually attach to the growing chain (polypeptide chain)

6. Steps in Translation Step 2
Ribosome forms a peptide bond between the first two amino acids
The bond between the trna and the amino acid is broken
The trna leaves the ribosome and the next trna attaches to the next codon on the mrna strand

7. Steps in Translation Step 3
The process will continue until a stop codon is reached
Stop codon = polypeptide chain and mrna strand are released from the ribosome
Process completed!

8. Roles of rna mrna rrna trna
Mrna carries the coded message from the dna molecule in the nucleus to the cytoplasm outside of the nucleus
Transcription: Dna codes for the mrna strand that will be taken out of the nucleus and used to make proteins
Ribosomes are composed of protein and rrna molecules
They hold the ribosomes in place for translation and find the start of the mrna
They help in the chemical reaction that holds the amino acids together
Trna delivers the exact anticodon to the codons on the mrna strand – anticodons code for amino acids
It helps “read” the coded mrna strand and turn it into protein
Translation: turning mrna code into protein

9. Molecular basis for heredity
What does protein have to do with genes?
Proteins are enzymes that catalyze reactions
The proteins stimulate color in a flower, patterns of growth, etc.
Proteins build or operate components of a cell
Central dogma
Information is transferred from Dna  rna  protein
Helps to discuss gene expression
Exceptions: viruses work differently