1 Review How does a cell interpret the genetic code Explain What are codons and anticodons2 Review What happens during translation Compare and Contrast How is protein synthesis

different from DNA replication3 Review Why is the genetic code considered universal Infer In what way does controlling the proteins in an

organism control it’s characteristics4 Choose one component of translation. Write a

question about that component and use it to form a hypothesis that could be tested in an experiment

CH 13 RNA AND PROTEIN SYNTHESIS13.2 Ribosomes and Protein Synthesis

Proteins are made from long chains of amino acids or polypeptides

20 different amino acids Order of amino acids make proteins different.

Codon

Each three-letter “word” in mRNA Consists of three consecutive bases that specify a

single amino acid.

How to Read Codons

Four different bases in RNA, so 64 possible three-base codons (4×4×4 = 64)

To read a codon, start at the middle of the circle and move outward.

Starts with AUG Has three stop codons.

Translation

Decoding of an mRNA message into a protein From RNA to protein Different languages.

Translation Steps

mRNA is transcribed in the nucleus and then enters the cytoplasm for translation.

Ribosome attaches to an mRNA molecule

Ribosome reads each codon of mRNA

Directs tRNA to bring the specified amino acid

Ribosome then attaches each amino acid to the growing chain.

tRNA has three unpaired bases or anticodon which is complementary to one mRNA codon

Codon AUG Anticodon UAC.

Next codon is UUC tRNA molecule with an AAG anticodon brings the

amino acid to ribosome.

Ribosome helps form a peptide bond between 1st and 2nd amino acid

Bond between tRNA molecule and amino acid is broken

tRNA shifts to 3rd site.

Ribosome moves over one codon New tRNA enters ribosome Process repeats itself.

Translation continues until a stop codon Ribosome release polypeptide and mRNA.

Molecular Basis of Heredity

Most genes contain instructions for assembling proteins.

Proteins Can

Be enzymes Produce pigment or odor Regulate growth Trigger development Operate cell parts.

Gene Expression

What DNA actually ends up doing How the genes gets expressed or shown.

Genetic code is nearly universal in all living organisms.

1. A certain gene has the following base sequence GACAAGTCCACAATC

2. Write this sequence down 3. From left to right, write the sequence of mRNA

molecule transcribed from this gene4. Using the figure on pg. 311, read the mRNA from

left to right and write down the amino acid sequence

5. Repeat step 3 reading the codons from right to left.

Analyze and Conclude

1. Apply Concepts Why did steps 3 and 4 produce different polypeptides

2. Infer Do cells usually decode nucleotides in one direction only or in either direction