Trait

Chapter 12 Section 3

Ribonucleic acid

Responsible for the movement of genetic information from the DNA in the nucleus to

the site of protein synthesis in the

cytosol

1. RNA

A. Structure of RNA:–Single-stranded Nucleic acid made up of repeating units, like DNA

–Sugar molecule is RIBOSE (not deoxyribose)

–Thymine is replaced with URACIL (U)

1.Messenger RNA (mRNA)a. STRUCTURE= RNA nucleotides in a single uncoiled chain

b. FUNCTION= Carries genetic info from the nucleus to the ribosome

2.Transfer RNA (tRNA)

a. STRUCTURE= RNA nucleotides in a single chain folded into a cloverleaf shape

b. FUNCTION= binds to specific amino acids and helps form polypeptide chains

3. Ribosomal RNA (rRNA)

a. STRUCTURE = RNA nucleotides in a globular form

b. FUNCTION = makes up the ribosomes where proteins are made

•The production of proteins•The amount and kind of

proteins produced in a cell determine the structure and function of the cell

•Protein’s carry out the genetic instructions encoded in an organism’s DNA

•Proteins are POLYMERS•Made up of amino acids•There are 20 different amino acids that make up proteins

a. Transcription

•What is it???–making mRNA from DNA

•NOTE: –Transcribe = to copy

T r a n s c r i p t i o n

1.RNA polymerase binds to DNA at the promoter and separates the DNA strands.

2.RNA polymerase then uses one strand of DNA as a template. Using the template as a guide, nucleotides are assembled into a strand of mRNA.

T r a n s c r i p t i o n Steps

DO NOW: Transcription

• 1. Where does Transcription occur?

• 2. What is produced at the end of transcription?

• 3. What enzyme is used in transcription?

b. T r a n s l a t i o n

STEP 2 of PROTEIN SYNTHESIS

•The process TRANSLATING the message encoded in mRNA to assemble a protein.

•Process begins when mRNA leaves the nucleus through pores in the nuclear membrane

•The mRNA then migrates to a ribosome in the cytosol, the site of protein synthesis

T r a n s l a t i o n

THE GENETIC CODE

•The genetic information necessary for making proteins is encoded in series of three mRNA nucleotides

•Each combination of 3-mRNA nucleotides is called a CODON

•Each codon codes for a specific amino acid

tRNA carries the

“Anticodon”

. . . Allows tRNA to match up with mRNA

codon

Codons in mRNA

If the mRNA sequence is

A-A-U (codon)

then the tRNA sequence is

U-U-A (anticodon)

1.mRNA arrives at a ribosome

2.mRNA is pulled through the ribosome

3.Start codon signals tRNA to start arriving

T r a n s l a t i o n Steps

4. One tRNA matches up to the codons on mRNA to deposit an amino acid

5. Another tRNA comes in and adds another amino acid to the chain.

6. Process continues until stop codon is reached and enough amino acids have been linked to form a protein.

T r a n s l a t i o n

Mutations•Mutations = errors

–Mutations can occur as a “typo” in the sequence of nitrogen bases.

–For example if a sequence should be A-C-G, a mutation could occur and it is now A-G-C . . . What affect could this have on the protein produced?

PROTEIN SYNTHESIS ANIMATION