Chapter 14: Protein Synthesis

Chapter 14 Protein Synthesis - Overview The DNA of the gene is transcribed into RNA Which is translated into protein The flow of genetic information from DNA to RNA to Protein is called the CENTRAL DOGMA DNA Transcription RNA Translation Protein

Chapter 14 Protein Synthesis (Overview) Central Dogma - FLOW IS FROM DNA TO RNA TO PROTEIN

FLOW IS FROM DNA TO RNA TO PROTEIN Chapter 14 Protein Synthesis (Overview) FLOW IS FROM DNA TO RNA TO PROTEIN Genes on DNA are expressed through proteins, which provide the molecular basis for inherited traits A particular gene, is a linear sequence of many nucleotides Specifies a polypeptide (long protein made of amino acids)

Chapter 14 Protein Synthesis (Overview) Genes - discrete units of hereditary information comprised of a nucleotide sequence found in a DNA molecule.

Messenger (mRNA) Monomer: nucleotide Parts of a mRNA Nucleotide Ribose Sugar Phosphate Nitrogenous Base Three main differences between mRNA and DNA Ribose instead of deoxyribose mRNA is generally single stranded mRNA has uracil in place of thymine (U instead of T)

RNA Three Types of RNA Messenger RNA (mRNA) – carries copies of genes (DNA) to the rest of the cell. Ribosomal RNA (rRNA) – make up the ribosomes. Transfer RNA (tRNA) – transfers the amino acids to the ribosomes as specified by the mRNA

TRANSCRIPTION: The process of making mRNA from DNA Why do you need this process? Location of DNA? Nucleus Location of Ribosome? Cytoplasm mRNA takes code from DNA in the nucleus to the cytoplasm Strand to be transcribed T A C DNA A T G Transcription A U G A A G U U U U A G RNA Start condon Stop condon Translation Polypeptide Met Lys Phe

Transcription produces genetic messages in the form of mRNA A close-up view of transcription RNA polymerase RNA nucleotides Direction of transcription Template Strand of DNA Newly made RNA T C A G U

In the nucleus, the DNA helix unzips And RNA nucleotides line up along one strand of the DNA, following the base pairing rules As the single-stranded messenger RNA (mRNA) peels away from the gene The DNA strands rejoin RNA polymerase RNA nucleotides Direction of transcription Template Strand of DNA Newly made RNA T C A G U

Transcription of a gene RNA polymerase DNA of gene Transcription of a gene Initiation Elongation Termination Promoter DNA Terminator DNA 1 Initiation Area shown In Figure 10.9A 2 Elongation Growing RNA 3 Termination Completed RNA RNA polymerase

Eukaryotic mRNA is processed before leaving the nucleus Exon Intron Exon Intron Exon DNA Cap Transcription Addition of cap and tail RNA transcript with cap and tail Introns removed Tail Exons spliced together mRNA Coding sequence Nucleus Cytoplasm Eukaryotic mRNA is processed before leaving the nucleus Noncoding segments called introns are spliced out leaving only the coding exons A 5’ cap and a poly A tail are added to the ends of mRNA Cap and tail protect mRNA 5’ 3’

T C C A A T A U T C T G U G A C C A U C C A C G A A T A G G T T Direction of transcription

13.2 Translation tRNA molecules Growing polypeptide (protein) mRNA Small subunit Growing polypeptide (protein) Large subunit

Protein Synthesis - Translation Translation is defined as going from mRNA to protein tRNA which have amino acids attached are going to the ribosome. What are amino acids? monomers of proteins Does the order of amino acids matter? Yes, they must be in order for the protein to fold correctly. How does the correct tRNA (with amino acid attached) bind to the mRNA? The tRNA contains an anticodon which matches up with the mRNA sequence (codon).

Transfer RNA (tRNA) molecules serve as interpreters during translation Takes place in the cytoplasm A ribosome attaches to the mRNA and translates its message into a specific polypeptide aided by transfer RNAs (tRNAs) tRNAs can be represented in several ways Amino acid attachment site Amino acid attachment site Hydrogen bond RNA polynucleotide chain Anticodon Anticodon

Translation Each tRNA molecule A specific amino acid Is a folded molecule bearing a base triplet called an anticodon on one end A specific amino acid Is attached to the other end Amino acid attachment site Anticodon

Ribosomes build polypeptides (proteins) Translation Ribosomes build polypeptides (proteins) A ribosome consists of two subunits Each made up of proteins and a kind of RNA called ribosomal RNA Translation at Ribosome tRNA molecules mRNA Small subunit Growing polypeptide Large subunit

Translation The subunits of a ribosome Hold the tRNA and mRNA close together during translation tRNA-binding sites Large subunit Next amino acid to be added to polypeptide Growing polypeptide tRNA mRNA- binding site mRNA Small subunit Codons

An initiation codon marks the start of an mRNA message mRNA, a specific tRNA, and the ribosome subunits assemble during initiation Met Initiator tRNA 1 2 mRNA Small ribosomal subunit Start codon Large ribosomal subunit A site U A C A U G P site

Elongation adds amino acids to the polypeptide chain until a stop codon terminates translation Once initiation is complete amino acids are added one by one to the first amino acid The mRNA moves a codon at a time A tRNA with a complementary anticodon pairs with each codon, adding its amino acid to the peptide chain

Each addition of an amino acid Occurs in a three-step elongation process Amino acid Polypeptide P site A site Anticodon mRNA Codons 1 Codon recognition mRNA movement Stop codon 2 Peptide bond formation New Peptide bond Figure 10.14 3 Translocation

Figure out the exact sequence of amino acids needed Take the DNA and transcribe it into mRNA Example: TAC ATA CTA GCG ACT mRNA: Take the mRNA sequence and decode it using the codon chart. AUG UAU GAU CGC UGA AUG = MET UAU = TYR GAU = ASP CGC = ARG Animation

Mutations Mutations – heritable changes in genetic information (changes to the DNA sequence) Two types - gene and chromosomal mutations Mutations can be caused by chemical or physical agents (mutagens) Chemical – pesticides, tobacco smoke, environmental pollutants Physical – X-rays and ultraviolet light

Mutations Gene mutations Point Mutation: mutations that affect a single nucleotide Frameshift mutation: shift the reading frame of the genetic message. Can change the entire protein so it doesn’t work Gene Mutations Explained

Mutations

Chromosomal Mutations Chromosomal mutation: mutation that changes the number or structure of chromosomes.

Chromosomal Mutations Types of chromosomal mutations: Deletion: The loss of all or part of a chromosome Duplication: A segment is repeated Inversion: part of the chromosome is reverse from its usual direction. Translocation: one chromosome breaks off an attaches to another chromosome.