PROTEIN SYNTHESIS Higher Level

Lesson Objectives At the end of this lesson you should be able to Outline the steps in protein synthesis Understand that a strand of DNA is copied by transcription Understand the role of mRNA Know the function of a ribosome in protein synthesis Understand the process of translation that leads to the formation of a new protein Know that the shape of a protein determines its function

For Protein Synthesis You need: A supply of amino acids – cytoplasm Instructions as how to join the amino acids together – genetic code An assembly line – ribosomes A messenger to carry information from DNA to ribosomes

Protein Synthesis - Steps 3 stages: 1. Transcription 2. RNA processing 3. Translation Remember: DNA  RNA  Protein

RNA is composed of 3 parts Ribose: smaller sugar than deoxyribose of DNA Phosphate 4 Nitrogenous Bases A,G,U,C RNA is single stranded and thus smaller & able to leave the nucleus of the cell

DNA  RNA  Protein Eukaryotic Cell Transcription Translation DNA mRNA Nuclear membrane Transcription RNA Processing Translation DNA mRNA Ribosome Protein Eukaryotic Cell

Prokaryotic Cell – No nucleus DNA  RNA  Protein Transcription Translation DNA mRNA Ribosome Protein Prokaryotic Cell – No nucleus

Learning Check What is RNA composed of? How does RNA (ribonucleic acid) differ from DNA (deoxyribonucleic acid)? What are the three stages in Protein synthesis?

1. Transcription Eukaryotic Cell DNA mRNA Ribosome Protein Nuclear membrane Transcription RNA Processing Translation DNA mRNA Ribosome Protein Eukaryotic Cell

1. Transcription The transfer of information in the nucleus from a DNA molecule to an RNA molecule. Only 1 DNA strand serves as the template Starts at promoter DNA (AUG) Ends at terminator DNA (stop) When complete, mRNA molecule is released into the cytoplasm

Video Clip available in extra material folder

Transcription Takes places in the nucleus of the cell The process by which the information from DNA is transferred to RNA. DNA uncoils and unzips. The exposed DNA bases are matched up with RNA bases in the nucleus to form mRNA.

1. Transcription DNA mRNA RNA Polymerase Enzyme

It was made in the nucleus by transcription from a DNA molecule. This is a molecule of messenger RNA. It was made in the nucleus by transcription from a DNA molecule. codon A U G G G C U U A A A G C A G U G C A C G U U mRNA molecule

Learning Check What type of RNA molecule is responsible for taking the DNA copy from the nucleus into the cytoplasm What parts of the cell do you find RNA in? Can you outline the stages in transcription?

2. RNA Processing Eukaryotic Cell DNA mRNA Ribosome Protein Nuclear membrane Transcription RNA Processing Translation DNA mRNA Ribosome Protein Eukaryotic Cell

2. RNA Processing Occurs in the nucleus. Non- Coding regions taken out by enzyme and Coding regions come together. End product is a mRNA molecule that leaves the nucleus to the cytoplasm.

mRNA Takes places in the nucleus of the cell The process by which the information from DNA is transferred to RNA. DNA uncoils and unzips. The exposed DNA bases are matched up with RNA bases in the nucleus to form mRNA.

Types of RNA Three types of RNA: A. messenger RNA (mRNA) B. transfer RNA (tRNA) C. ribosome RNA (rRNA) Remember: all produced in the nucleus!

A. Messenger RNA (mRNA) Carries the information for a specific protein. Made up of 500 to 1000 nucleotides long. Made up of codons (sequence of three bases) Each codon is specific for one amino acid.

A. Messenger RNA (mRNA) Primary structure of a protein A U G C aa1 aa2 start codon codon 2 codon 3 codon 4 codon 5 codon 6 codon 7 codon 1 methionine glycine serine isoleucine alanine stop codon protein Primary structure of a protein aa1 aa2 aa3 aa4 aa5 aa6 peptide bonds

B. Transfer RNA (tRNA) Made up of 75 to 80 nucleotides long. Picks up the appropriate amino acid floating in the cytoplasm Transports amino acids to the mRNA. Has anticodons that are complementary to mRNA codons. Recognizes the appropriate codons on the mRNA and bonds to them with H-bonds.

C. Ribosomal RNA (rRNA) Made up of rRNA is 100 to 3000 nucleotides long. Important structural component of a ribosome. Associates with proteins to form ribosomes.

Ribosomes Large and small subunits. Composed of rRNA (40%) and proteins (60%). Both units come together and help bind the mRNA and tRNA.

Ribosomes Large subunit mRNA A U G C Small subunit

Learning Check What are the three types of RNA? Where is each type produced? What is the function of each type of RNA?

3. Translation Eukaryotic Cell DNA Pre-mRNA mRNA Ribosome Protein Nuclear membrane Transcription RNA Processing Translation DNA Pre-mRNA mRNA Ribosome Protein Eukaryotic Cell

Video Clip available in extra material folder

3. Translation Synthesis of proteins in the cytoplasm Involves the following: 1. mRNA (codons) 2. tRNA (anticodons) 3. rRNA 4. ribosomes 5. amino acids

3. Translation Three parts: 1. initiation: start codon (AUG) 2. elongation: 3. termination: stop codon (UAG)

Translation In the cytoplasm, translation occurs. The mRNA binds to a ribosome. The strand of mRNA is pulled through the ribosome three bases at a time, in triplets. Each of these triplets on the mRNA strand is called a codon.

It was made in the nucleus by transcription from a DNA molecule. This is a molecule of messenger RNA. It was made in the nucleus by transcription from a DNA molecule. codon A U G G G C U U A A A G C A G U G C A C G U U mRNA molecule

A ribosome on the rough endoplasmic reticulum attaches to the mRNA molecule. A U G G G C U U A A A G C A G U G C A C G U U

Amino acid U A C tRNA molecule A transfer RNA molecule arrives. It brings an amino acid to the first three bases (codon) on the mRNA. anticodon The three unpaired bases (anticodon) on the tRNA link up with the codon. A U G G G C U U A A A G C A G U G C A C G U U

U A C C C G Another tRNA molecule comes into place, bringing a second amino acid. Its anticodon links up with the second codon on the mRNA. A U G G G C U U A A A G C A G U G C A C G U U

C C G A A U Another tRNA molecule brings the next amino acid into place. A U G G G C U U A A A G C A G U G C A C G U U

C C G C C G A peptide bond joins the second and third amino acids to form a polypeptide chain. A U G G G C U U A A A G C A G U G C A C G U U

A C G G U C The process continues. The polypeptide chain gets longer. This continues until a termination (stop) codon is reached. The polypeptide is then complete. A U G G G C U U A A A G C A G U G C A C G U U

tRNA Transfer RNA (tRNA), reads the strand of mRNA and translates it into a strand of amino acids. A molecule of tRNA has at one end a set of three bases that will complement the mRNA strand; this is called the anticodon.

tRNA If the 3 base anticodon of the tRNA complements the 3 base codon of the mRNA, they briefly combine. The amino acid is left behind when the tRNA leaves. As each codon is read, the next tRNA brings in a new amino acid and the polypeptide (protein) chain grows. This requires enzymes and ATP.

End Product 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

Functional Protein The protein now has to undergo folding and the addition of bonds Folding allows the Protein to reach its 3D (Tertiary Shape) which influences its Function.

Learning Check The anticodon UAC belongs to a tRNA that recognizes and binds to a particular amino acid. What would be the DNA base code for this amino acid?

Answer: tRNA - UAC (anticodon) mRNA - AUG (codon) DNA - TAC

What have you learned? Can you ………………  Outline the steps in protein synthesis Understand that a strand of DNA is copied by transcription Understand the role of mRNA Know the function of a ribosome in protein synthesis Understand the process of translation that leads to the formation of a new protein Know that the shape of a protein determines its function

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