Review of Protein Functions

Protein Synthesis Protein synthesis is divided into two

phases: TRANSCRIPTION and TRANSLATION

I. TranscriptionA. RNA polymerase unzips DNA

(NOT making more DNA, just reading it)

– Free RNA nucleotides are base-paired with the exposed DNA nucleotides and assembled into a messenger RNA (mRNA) molecule by RNA polymerase.

C. The mRNA molecule leaves the nucleus and moves to a ribosome in the cytoplasm

Draw Fig 12-14, pg 301

RNADNA

RNApolymerase

Adenine (DNA and RNA)Cystosine (DNA and RNA)Guanine(DNA and RNA)Thymine (DNA only)Uracil (RNA only)

II. Translation (4 Stages)

A. Amino Acid Activation Stage1. The amino acids are attached to

their appropriate tRNA molecules.2. Specific enzymes bind each tRNA

with only one specific amino acid.3. This process begins during

transcription.4. A molecule of ATP transfers its high

energy bond to the activated tRNA.

B. Initiation Stage1. The ribosome moves along the mRNA

molecule, but nothing happens until the codon (AUG) is read.

2. AUG is known as the “Start Codon” and it codes for the amino acid f-methionine.

3. When this codon is reached, the elongation stage begins.

C. Elongation Stage (3 Steps)1. New incoming tRNA matches its anti-codon with the mRNA codon.

a. At the start, step 1 is repeated one time

mRNA

tRNAamino acid

Ribosome

b. Notice how the tRNA anti-codon pairs with the mRNA codon.

2. The amino acid on the first tRNA is transferred to the amino acid on newly arrived tRNA.

3. The empty tRNA leaves.

a. Now another tRNA positions itself beside the 2nd tRNA and amino acids are transferred from the 2nd tRNA to the 3rd tRNA

b. The ribosome continues along the mRNA molecule and steps 1,2 and 3 are repeated over and over again.

What do we call this string of amino acids?

D. Termination phase 1. Elongation continues until a stop

codon is reached.

a. An mRNA codon (UGA, UAG, UAA) for which there is no matching tRNA anticodon (ACU, AUC, AUU)

2. The amino acid chain (protein) is released and the process is complete.

Short Quiz

1. What brought each amino acid to the growing protein?The tRNA molecule

2. What determined which tRNA and amino acid would be place in order in the ribosome?The mRNA molecule

3. What determined the mRNA code?

The DNA molecule

III. DNA and GenesA. What is a gene?

A segment of DNA that codes for a proteinB. What does a gene start with?

An initiation codon (AUG)

C. What does a gene end with?A stop codon (UAG, UAA or UGA)

D. How many genes are in a DNA molecule?Depends on species, but can be thousands.

E. The Central Dogma DNA is transcribed into RNA, which is

then translated into a protein that is expressed as a trait

IV. MutationsA. A mutation is any change in an organisms’

DNA

B. Point mutations are a change in one or more nucleotides

1. Substitution – replacement of one nucleotide and its complementary partner with another pair of nucleotides

2. Frameshift – addition or deletion of a nucleotide shifts the codons, changing every amino acid that follows the point of mutation

Insertion

Deletion

C. Chromosomal mutations involve a change in the number or structure of chromosome

4 Types:

1. Deletion – loss of all or section of chromosome

2. Duplication – produces extra copies of sections

3. Inversion – reverse the direction of sections

4. Translocation – section breaks off and attaches to another chromosome

Deletion

Duplication

Inversion

Translocation

DRAW Chromosomal MutationsFigure 12-21, pg 308

Chromosome Mutation Movie

D. Significance of mutations1. Most mutations are neutral, but

some can result in a beneficial or harmful trait

2. Associated with many types of cancer

3. Source of genetic variability in species