Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
DNA and Protein Synthesis Biology 12 Chapter 24 Overview/Objectives • Part 1: DNA I. DNA structure II. Functions of DNA III. DNA Replication • Part 2: Protein Synthesis (Gene Expression) I. RNA II. Protein Synthesis a. b. Transcription Translation III. Mutations Part 1: DNA DNA = Deoxyribonucleic Acid = The genetic material of all living things = Contains all of the “instructions” needed for life I. DNA structure • Determined by Watson and Crick in the early 1950’s • Made up of nucleotides each nucleotide has 3 subunits: o Phosphate group o Pentose sugar (deoxyribose) o Nitrogen-containing base • 4 possible bases: Purines (Double Ring) Pyrimidines (Single Ring) Adenine (A) pairs with Thymine (T) Guanine (G) pairs with Cytosine (C) Complementary base pairing Done by hydrogen bonds • DNA is a double stranded molecule o Strands are held together by hydrogen bonding o Alternate Sugar-Phosphate backbone o Strands twist to form a double helix o Two strands run antiparallel (in opposite directions) II. Functions of DNA 1. Store information: control cell activity via. Genes 2. Have mutations: allows for evolution 3. Replicate: make copies of self before cell division to ensure daughter cells get equal amount of DNA III. DNA Replication • Needed when a cell divides each new cell needs a copy of the DNA • Semi-conservative replication each new double helix has one old strand and one new strand Steps to DNA Replication 1. Enzyme DNA helicase unwinds and unzips the double-stranded DNA, breaking the hydrogen bonds 2. New nucleotides base-pair to parent strands helped out by enzyme DNA polymerase 3. Enzyme DNA ligase seals the sugarphosphate backbone 4. 2 double helix molecules identical to each other, having one parent and one new strand Part 2: Protein Synthesis (Gene Expression) • Gene: A segment of DNA that specifies the amino acid sequence of a protein • Genes pass their info to RNA RNA is involved in protein synthesis I. RNA • RNA = Ribonucleic Acid • Type of nucleic acid consisting of: o Ribose sugar o Phosphate o Base: adenine, guanine, uracil, cytosine o Single stranded RNA vs. DNA Sugar Ribose Deoxyribose Bases AGUC AGTC Strand single double Helix no yes Types of RNA 3 types: • Messenger RNA (mRNA): Takes a message from DNA to ribose • Ribosomal RNA (rRNA): Along with proteins, make up the ribosomes (location of protein synthesis) • Transfer RNA (tRNA): Transfers amino acids to the ribosome II. Protein Synthesis • Two steps involved with protein synthesis a) Transcription genetic information is transferred from DNA to RNA b) Translation RNA transcript directs the sequence of amino acids in the polypeptide (protein) a) Transcription (step 1) • Process of creating mRNA from a DNA template 1. Enzyme RNA polymerase binds to a promoter (special nucleotide sequence) on DNA, and opens up the DNA helix a) Transcription (step 2) 2. Complementary base pairing occurs and RNA polymerase joins the RNA nucleotides, forming an RNA molecule a) Transcription (step 3) 3. Processing of RNA I. One end is “capped”(addition of altered guanine nucleotide) Addition of poly-A-tail to the other end II. Introns removed, exons joined a) Transcription (step 4) 4. Mature mRNA leaves the nucleus through a nuclear pore and enters cytoplasm The Genetic Code • Triplet code every 3 bases of mRNA codes for 1 amino acid – Each 3 letter (nucleotide) unit of mRNA is called a codon • tRNA brings amino acids to ribosomes: one end holds the amino acid, the other end contains an anticodon a group of 3 bases complementary to a codon on mRNA Example: Reading the Genetic Code Which amino acid sequence is formed from the DNA strand: GGT ACA TAG CAC DNA CCA UGU AUG GUG mRNA proline-cysteine-isoleucine-valine amino acids Use table 24.8 p.492 b) Translation • The step by which gene expression leads to protein synthesis • 3 steps: 1. Chain initiation 2. Chain elongation 3. Chain termination b) Translation (step 1) Chain Initiation • Smaller ribosomal subunit binds mRNA • Initiator tRNA binds • Larger ribosomal subunit binds, completing the ribosome b) Translation (step 2) Chain Elongation • tRNA binds in 2nd binding site of ribosome • Peptide bond forms between amino acids • tRNA in 1st binding site leaves, ribosome moves down mRNA (translocation) • tRNA in 2nd binding site has moved to 1st binding site… cycle continues… b) Translation (step 3) Chain Termination • Stop codon on mRNA reached • Polypeptide (amino acid chain) is cleaved from the last tRNA • Ribosome separates and releases mRNA III. Mutations Mutation= any alteration in the code or expression of the code (DNA) Causes of Mutations: • Errors in Replication • Mutagens (environmental influences) • Transposons (DNA sequences that move between chromosomes) Types of Mutations: • Frame shift mutation (nucleotides are inserted or deleted) • Point mutation (substitution of one nucleotide for another)