UNDERSTANDING HEREDITY

PROTEIN SYNTHESIS

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Genes & ProteinsGenes & Proteins• Genes - sequences of

nucleotide bases• Genes code for proteins• Proteins - amino acids linked

together by peptide bonds• 20 different amino acids exist

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Genes & ProteinsGenes & Proteins•Amino acid

chains are called polypeptides

• So: Protein = polypeptide

Ribbon Structure ofMouse Cholera

Antibody

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Starting with DNAStarting with DNA• DNA - found inside the

nucleus• Proteins are made in the

cytoplasm of cells by organelles called ribosomes

• Ribosomes may be free in the cytoplasm or attached to the surface of rough ER

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Starting with DNAStarting with DNA• DNA ‘s code must be

copied and taken to the cytoplasm

• In the cytoplasm, this code must be read so amino acids can be assembled to make proteins

• This process is called protein synthesis

RNARNA

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Roles of RNA & DNA•DNA = COOKBOOK

•RNA = KITCHEN CREW

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Roles of RNA & DNARoles of RNA & DNA• RNA is a RNA is a disposabledisposable copy of a copy of a

portion of DNAportion of DNA• It is used to It is used to constructconstruct a a proteinprotein• Comparison of RNA and DNAComparison of RNA and DNA

RNA DNA

Sugar Ribose Deoxyribose

Nitrogen Bases C G A U(racil) C G A T

Structure Single Helix Double Helix

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. Three Types of RNAThree Types of RNA

• Messenger RNA - mRNA• Ribosomal RNA - rRNA• Transfer RNA - tRNA

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Messenger RNA (recipe)

• Long chain of nucleotides

• Made in the nucleus• Transcribes DNA &

leaves through nuclear pores

• Carries information for a specific protein to ribosome

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Ribosomal RNA (head chef)

• rRNA is a single strand 100 to 3000 nucleotides long

• Globular in shape• Made in the

nucleolus of a cell• Reads mRNA and

assembles proteins

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Transfer RNA (kitchen Transfer RNA (kitchen staff)staff)

• Clover-leaf shape

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

• Found out in the cytoplasm

• Brings amino acid to ribosome

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The Genetic Code• Codon - a set of three RNA

bases

• Codon - designates a specific amino acid

• An amino acid may have more than one codon and there are 64 codons

TranscriptiTranscription and on and TranslationTranslation

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Protein SynthesisProtein 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

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TranscriptionTranscription• The process of mRNA copying

the sequence of one strand of DNA

• During transcription, RNA polymerase binds to DNA and separates the DNA strands

• RNA Polymerase then uses one strand of DNA as a template to assemble nucleotides into RNA

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• What would be the mRNA strand for the following DNA sequence?

DNA 5’-GCGTATGAA-3’DNA 5’-GCGTATGAA-3’

mRNA 3’-CGCAUACUU-5’mRNA 3’-CGCAUACUU-5’

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STEPS OF TRANSCRIPTON:STEPS OF TRANSCRIPTON:1.RNA polymerase binds to DNA just before code for protein begins2.Nucleotide bases are added to make strand of mRNA3.RNA polymerase detaches from DNA and mRNA4.Enzymes proofread the mRNA sequence before it leaves nucleus

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mRNA Transcript•mRNA leaves the nucleus through its pores and goes to the ribosomes

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TranslationTranslation

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

•Ribosomes read mRNA three nucleotide bases or 1 codon at a time

STEPS OF TRANSLATION:1.mRNA transcript start codon AUG attaches to the ribosome2.Amino acids are brought to the ribosome by tRNA3.tRNA plugs into the mRNA with an anticodon4.The amino acids are attached like beads on a string5.tRNA is released to cytoplasm; mRNA is disassembled6.Stop codon tells ribosome to release protein

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Summary of Protein Summary of Protein SynthesisSynthesisTranscription Translation

DNA mRNA tRNA amino acid protein code copy anticode assemble product

Mutations are Mistakes• Mistakes in gene code cause

mistakes in the protein• These mistakes are called

mutations• In protein synthesis mutations

involving one base are called point mutations

• Some mutations may do nothing to the final protein others may do serious damage

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