Chapter 10

Protein Synthesis

DNA has the code to make proteins

• DNA contains the instructions for the cell:– It tells it how to make copies of cells:

• Body (somatic) cells are copied by mitosis• Sex cells are copied by meiosis

– It tells it how to make proteins which have many functions in the cytoplasm of the cell.

Proteins are important

• Proteins make up genes, which determine your genetic traits (hair color, height, etc.)

• Proteins act as catalysts to speed up chemical reactions.

• Proteins direct the chemical reactions in your cells and “tell the cell organelles” what to do.

• IN SUMMARY – Proteins are the instructions of the DNA in action.

DNA review

• Nucleic acids are made up of monomers of units called nucleotides:

Sugar, phosphate and base

• DNA sugar is DEOXYRIBOSE• There are two strands in DNA (the two sides)• The bases in DNA are : A,T,C,G• AG are purines, CG are pyrimidines• DNA NEVER LEAVES THE NUCLEUS

RNA is a little different

• RNA is a single strand• R stands for RIBOSE which is the sugar.• There are two kinds of RNA:

– mRNA which is formed in the nucleus– tRNA which is in the cytoplasm

• The bases of RNA are : C,G and A, U (not T)• mRNA LEAVES the nucleus and goes to the

ribosome where protein synthesis occurs.

Protein synthesis is a series of STEPS

• 1. mRNA gets instructions from DNA– This is called TRANSCRIPTION

• 2. mRNA leaves the nucleus and takes the instructions to the ribosome.

• 3. mRNA gives the message to the t RNA– This is called TRANSLATION

The tRNA attaches AMINO ACIDS together to FORM PROTEINS

– This is called Protein Synthesis• 4. PROTEINS coil up to form shapes that can act as

enzymes and bond with substrates.

STEP 1 – called TRANSCRIPTION

A. DNA uncoils when an enzyme tells the DNA to unwind. This creates a REPLICATION FORKB. The RNA POLYMERASE puts the mRNA nucleotides together along the DNA strands, adding the complementary bases and proofreading them.

Step ONE

Step 2

• mRNA leaves the nucleus and takes the instructions to the ribosome.

Step 2

Step 3

A. mRNA gives the message to the t RNAThis is called TRANSLATION

B. The tRNA carries Amino Acids on it (every 3 bases on tRNA has an amino acid attached - these are called CODONS)C. The tRNA attaches AMINO ACIDS together to FORM PROTEINS

This is called Protein Synthesis

TRANSLATION

tRNA with amino acid attached

mRNA template

Protein formed from amino acids

Step 4: The Protein then coils up

The protein then can do its job

• Like catalyze (speed up) reactions when acting as an enzyme:

products

ACTIVE SITE

Reactant Substrate

EnzymeCatalyst

THE “CODE”

• The code for the tRNA to use to attach the amino acids together into the protein strand is found on the mRNA base sequence.

• Three bases make up the base sequence.• The three bases are called the CODON.• Scientists use tables to determine the correct

match of codon to amino acids.• There are 21 amino acids in the body.

Table found in Ch. 10Second nucleotide

Another type of codon table