Protein Synthesis

Definitions

1. Protein Synthesis: the construction of proteins directed by DNA

---------Consists of 2 steps, which are-----------

2. Transcription: copying DNA in the nucleus to mRNA

3. Translation: using mRNA as a guide to form a polypeptide (protein)

What part of the cell cycle?

S Phase G2 Phase

Mitosis

Definitions4. rRNA: ribosomal RNA

5. mRNA: messenger RNA

6. tRNA: transfer RNA

Where does protein synthesis happen?

• The ribosomes!

What are the monomers ribosomes use to build proteins?

• Amino acids

What are proteins used for?Type of Function

Example Function

Enzymes amylase Promotes breakdown of starch

Hormones insulin Regulates blood sugar levels

Structural keratin Hair, wool, nails, horns, hoofs, etc.

Transport hemoglobin Carries oxygen in blood

Immune defense antibodies Rid the body of foreign proteins

Contractile actin Contracting fibers in muscles

How does protein synthesis happen?

This is known as the

central dogma

of Biology.

3 Differences between DNA & RNA

DNA:• Deoxyribose sugar• Contains thymine (T)

A-T and C-G

• Double-stranded

RNA:• Ribose sugar• Contains uracil (U)

instead of thymineA-U and C-G

• Single strand

3 Types of RNA

1. rRNAa. Location: nucleus and ribosomes

b. Function: combines with proteins to make ribosomes

3 Types of RNA2. mRNA

a. Location: nucleus and cytoplasm

b. Function: brings instructions from DNA in nucleus to ribosomes in the cytoplasm

mRNA

3 Types of RNA3. tRNA

a. Location: nucleus and cytoplasm

b. Function: brings amino acids to ribosome to build polypeptides (proteins)

tRNA

How are proteins made?

• Step 1: Transcription – RNA polymerase splits open DNA and copies it to form a strand of mRNA. mRNA leaves the nucleus.

How are proteins made?• Step 2: Translation – mRNA in the

cytoplasm binds to a ribosome. Ribosome reads it 3 bases at a time, and matches these with bases on tRNA attached to an amino acid. An amino acid chain is formed from many peptide bonds.

How are proteins made?

• Step 3: Protein folding – polypeptide is folded, and combined with other polypeptides to form a protein.

What is a codon?

• mRNA is read 3 bases at a time – a codon is the 3 base code, or triplet code, of mRNA.

What is a polypeptide?

• A long chain of amino acids linked by peptide bonds

How many different amino acids can each codon specify?

• Only one (CUC only codes for leucine)

Can an amino acid have more than one codon?

• Yes! (ex.: phe, leu, pro, thr, ala, val, gly, etc.)

Transcribe the DNA into mRNA, then translate it into amino acids.

Animations of Protein Synthesis

http://www.wisc-online.com/objects/index_tj.asp?objID=AP1302

http://www-class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a3.html

http://library.thinkquest.org/20465/g_DNATranscription.html

GAME:

http://learn.genetics.utah.edu/content/begin/dna/transcribe/