date goes here - crestwood middle school - translation.pdf · uag • don’t try to memorize the...

PROTEIN SYNTHESIS

Do these people represent DNA or RNA?

How do you know?

DNA

• DNA contains genes, sequences of nucleotide bases

• These Genes code for polypeptides (proteins)

• Proteins are used to build cells and do much of the work inside cells

Genes & Proteins

Proteins are made of amino acids linked together by peptide bonds

20 different amino acids exist

Amino Acid Structure

Polypeptides

• Amino acid chains are called polypeptides

Pathway to Making a Protein

DNA

mRNA

tRNA (ribosomes)

Protein

Protein Synthesis

The production or synthesis of polypeptide chains (proteins)

Two phases: Transcription

Translation

mRNA must be processed before it leaves the nucleus of eukaryotic cells

The Genetic Code • A codon designates an amino acid • An amino acid may have more than one codon

• There are 20 amino acids, but 64 possible codons

• Some codons tell the ribosome to stop translating

Codons

• Sets of 3 Base Pairs

• Each codes for an amino acid

• Redundancy

• Start codon AUG

Name the Amino Acids

• GGG?

• UCA?

• CAU?

• GCA?

• AAA?

What does it mean to translate?

To change from one form into another

Big Picture overview of transcription and translation:

Transcription: Making an RNA copy of the DNA

Translation: Making a protein from the RNA copy

How do we refine the central dogma to include transcription and translation?

Why not just use the DNA to make a protein?

So what is the biological understanding of TRANSLATION?

the process of matching amino acids to corresponding sets of three bases (codons) and linking them into a protein.

What are codons? AUGCCGUUAUUA

Each series of corresponding three bases

What are amino acids? 20 different small molecules that link together in

long chains to form proteins. Often referred to as the "building blocks" of

proteins.

How does TRANSLATION work?

1. You have a your resulting RNA strand from transcription

UGACUUGGACUA

2. Each codon is translated into a specific AMINO ACID

a. The tRNA reads the code on the mRNA and brings the right amino acid

b. The ribosome links the amino acids into a chain to make a protein

. Three Types of RNA

• Messenger RNA (mRNA) copies DNA’s code & carries the genetic information to the ribosomes

• Ribosomal RNA (rRNA), along with protein, makes up the ribosomes

• Transfer RNA (tRNA) transfers amino acids to the ribosomes where proteins are synthesized

Messenger RNA (mRNA)

• Long chain of nucleotides that carries the information for a specific protein

• Made in the Nucleus (500 – 1000 nucleotides long)

• Contains the Nitrogen Bases A, G, C, U ( no T )

• Copies DNA & leaves through nuclear pores

Transfer RNA (tRNA) • Clover-leaf shape

• Each tRNA carries a specific amino acid

• Single stranded molecule with attachment site at one end for an amino acid

• Opposite end has three nucleotide bases called the anticodon

– Anticodon: three tRNA nucleotides that will hydrogen bond with the mRNA codon

Codons and Anticodons

• The 3 bases of an anticodon are complementary to the 3 bases of a codon

• Example: – Codon ACU

– Anticodon UGA

U G A

A C U

Transfer RNA amino acid

attachment site

U A C

anticodon

Ribosomal RNA (rRNA)

• rRNA is a single strand 100 to 3000 nucleotides long

• Globular in shape

• Made inside the nucleus of a cell

• Associates with proteins to form ribosomes

• Site of protein Synthesis

Ribosomes

• Made of a large and small subunit

• Composed of rRNA (40%) and proteins (60%)

• Have two sites for tRNA attachment: – P and A

Ribosomal RNA (rRNA)

Messenger RNA (mRNA)

Ribosome

Transfer RNA (tRNA)

Amino acid

Codon

•Messenger RNA •Carries the message from the DNA

to the ribosome to build a protein

•Transfer RNA •Transfers amino acids

onto the protein as it is

being made

•Ribosomal RNA •Part of the ribosome

Translation

• Translation is the process of decoding the mRNA into a polypeptide chain

• Ribosomes read mRNA three bases or 1 codon at a time and construct the proteins

Key things to remember

• A protein always begins with the same START codon: RNA codon AUG and the amino acid methionine (met).

• A protein is finished when it reaches a STOP codon: RNA codons: UAA, UGA, UAG

• Don’t try to memorize the code. It will be given to you. Just learn the start codon.

Site of Translation: Ribosomes

P

Site

A

Site

Large subunit

Small subunit

mRNA

A U G C U A C U U C G

Step 1- Initiation

• mRNA transcript start codon AUG attaches to the small ribosomal subunit

• Small subunit attaches to large ribosomal subunit

mRNA transcript

Initiation

mRNA


2-tRNA

G

aa2

A U

A

1-tRNA

U A C

aa1

anticodon

hydrogen bonds codon

Step 2 - Elongation

• As ribosome moves, two tRNA with their amino acids move into site A and P of the ribosome

• Peptide bonds link the amino acids together

mRNA


1-tRNA 2-tRNA

U A C G

aa1 aa2

A U

A

anticodon

hydrogen

bonds codon

peptide bond Elongation

mRNA


1-tRNA

2-tRNA

U A C

G

aa1

aa2

A U

A

peptide bond

3-tRNA

G A A

aa3

Ribosomes move over one codon

(leaves)

mRNA


2-tRNA

G

aa1

aa2

A U

A

peptide bonds

3-tRNA

G A A

aa3

A C U

mRNA


2-tRNA

G

aa1 aa2

A U

A

peptide bonds

3-tRNA

G A A

aa3

4-tRNA

G C U

aa4

A C U

(leaves)


mRNA

G C U A C U U C G

aa1 aa2

A

peptide bonds

3-tRNA

G A A

aa3

4-tRNA

G C U

aa4

A C U

mRNA

G C U A C U U C G

aa1

aa2

A

peptide bonds

3-tRNA

G A A

aa3

4-tRNA

G C U

aa4

A C U

U G A

5-tRNA

aa5


37 mRNA

A C A U G U

aa1

aa2

U

primary

structure

of a protein

aa3

200-tRNA

aa4

U A G

aa5

C U

aa200

aa199

terminator

or stop

codon

Termination

38

End Product –The Protein!

• The end products of protein synthesis is a primary structure of a protein

• A sequence of amino acid bonded together by peptide bonds

aa1

aa2 aa3 aa4 aa5

aa200

aa199

Lysine

1. mRNA is transcribed in the nucleus.

NUCLEUS

mRNA

tRNA

RIBOSOME

2. mRNA enters cytoplasm & attaches to ribosome at the “start codon.”

3. tRNA with the correct anti-codon brings in the next amino acid in the sequence.

mRNA Start codon

Phenylalanine

Methionine

Lysine

mRNA

D i r e c t i o n o f t r a n s l a t i o n

tRNA

RIBOSOME

tRNA

RIBOSOME

Growing polypeptide chain

5. The ribosome moves along the mRNA to bind new tRNA molecules and amino acids.

6. The process continues until the ribosome reaches a stop codon.

4. The ribosome joins the two amino acids & releases the tRNA.

Key things to remember

• A protein always begins with the same START codon: RNA codon AUG and the amino acid methionine (met).

• A protein is finished when it reaches a STOP codon: RNA codons: UAA, UGA, UAG

• Don’t try to memorize the code. It will be given to you. Just learn the start codon.

Practice

Replication

DNA Strand:

A C T A C G T T A G A A C T

Complimentary Strand?

T G A T G C A A T C T T G A

Practice

Transcription

DNA:

A C T A C G T T A G A A C T

mRNA:

U G A U G C A A U C U U G A

Practice (use your amino acid decoder)

Translation

mRNA:

U G A U G C A A U C U U G A

Amino acid sequence:

met – gln – ser - STOP

date goes here - crestwood middle school - translation.pdf · uag • don’t try to memorize the...

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