understanding heredity protein synthesis 1. genes & proteins genes - sequences of nucleotide...
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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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