RNA & PROTEIN SYNTHESIS

Chapter 12

Section 3

Pages 300-306

I. RNA

A. What Is It?

1. RIBO-NUCLEIC ACID

- The “Middle-Man” between DNA (nucleus) & the ribosomes

(cytoplasm).

2. Structure

a. Ribose (Sugar)

b. Single-stranded, not double.

c. Thymine is replaced by URACIL.

- Adenine binds with Uracil.

d. RNA can be found inside and outside of the nucleus (DNA is always inside!)

II. What Codes For A Protein?

A. The genetic code allows for almost an infinite amount of different

proteins.

B. Every 3 bases of DNA (or mRNA) is referred to as a CODON.

- Each codon codes for 1 amino acid.

Example:

GCA codes for the amino acid Alanine.

C. Proteins are made outside the nucleus.Why?That is where they are needed the most!

III. Types of RNA

1. mRNA (Messenger RNA) a. A copy of the information

found in DNA.

b. Carries instructions to the ribosomes on how to

make a specific protein.

2. rRNA (Ribosomal RNA)

- make up ribosomes, which

direct the synthesis of a protein.

3. tRNA (Transfer RNA)

- carries amino acids to the

ribosomes where they are

connected to form proteins.

IV. STEPS IN PROTEIN SYNTHESIS

STEP 1: Transcription

A. The process whereby mRNA is made from DNA.

- Very similar to DNA Replication.

- Occurs inside the Nucleus.

1. An enzyme (RNA Polymerase) binds to

an area of DNA called a Promoter.

- Where Transcription will start.

2. RNA Polymerase unwinds & separates the DNA strand.

- One half will be used as a template to

make mRNA.

3. Complimentary “RNA” nucleotides

match up with each DNA base.

4. A single strand of mRNA continues to

grow until a “STOP” codon is reached.

Transcription in the nucleus

Transcription Animation

• http://www.biostudio.com/d_%20Transcription.htm

STEP 2: Translation

A. The process of converting the info. in mRNA into a protein.

- Occurs within the cytoplasm on a ribosome.

1. mRNA leaves the nucleus and binds to a ribosome, it will bind at AUG, which is the start codon for the amino acid methionine.

2. The ribosome moves along the mRNA and reads every three bases (codon).

3. tRNA (compliment of mRNA) picks up specific amino acids from the cytoplasm and attaches to the mRNA strand.

4. The “anticodon” of tRNA temporarily attaches to its complimentary codon on mRNA and adds its amino acid.• Amino acids are bonded with peptide bonds

forming a polypeptide

5. This process continues until a “STOP” codon is reached.

* When complete, a single protein has been produced.

Translation

Translation fill in

Translation Animation

• http://highered.mcgraw-hill.com/olc/dl/120077/micro06.swf

Mutations Pages 307-308

Ch. 12-4 Mutations

• Mutation – a change in a DNA sequence that affects genetic information

• Two types:

• 1. Gene mutation

• 2. Chromosomal

mutation

1. Types of MutationsA. Point Mutations

- A change in a single base pair.

Example:

Mrs. Cowley is cool! ATG TCA AAT CGA

Mrs. Cowley is _______? ATG TCA AAT GGA

B. Frameshift Mutations

- A mutation which causes an entire shift in the genetic message.

Examples:

ATG ACG GCA TTG TCT GGA

Deletion: ATG AGG CAT TGT CTG GA_

ATG ACG GCA TTG TCT GGA

Insertion: ATG ACT GGC ATT GTC TGG A

- The entire protein sequence has been changed!

Gene Mutations

C. Chromosomal Mutations

- Affects large sections of DNA rather

than smaller sections.

- Portions of a chromosome (s) can be added, deleted or reversed.

Example:

Down Syndrome (Trisomy 21)

- Child has 47, instead of 46 chromosomes.

* What are some characteristics of someone with Trisomy 21?

Deletion

Duplication

Inversion

Translocation