Unit 6 DNA Griffith Experiment DNA Structure DNA

Unit 6 DNA

Griffith Experiment

DNA Structure • DNA is a polymer made of monomers called nucleotides • Each nucleotide is made of: – A phosphate group – Deoxyribose (sugar) – Nitrogen containing base

DNA Structure • DNA is in the shape of a double helix • Each nucleotide is paired

Types of Nucleotides • C – Cytosine Pyrimidines • T – Thymine • A – Adenine Purines • G – Guanine

Base-Pairing Rules • Nucleotides always pair in the same way – Thymine (T) always pairs with Adenine (A) – Cytosine (C) always pairs with Guanine (G) – Ex. TTACGTAG AATGCATC

DNA Replication • Replication is a process by which DNA is copied • Occurs during the S stage of the cell cycle

DNA Replication • Enzymes are responsible for splitting and copying DNA • DNA polymerase- enzyme that binds DNA strands together

DNA Replication _____ • Steps of Replication: 1. DNA strand is unzipped 2. Free nucleotides bind to each template strand 3. Two identical DNA strands are formed

DNA Transcription • Transcription is the process of copying a sequence of DNA into a message called RNA • RNA is a temporary copy of DNA • Three types of RNA: 1. m. RNA- message 2. r. RNA- forms part of ribosomes 3. t. RNA- transfers amino acids to help make proteins

DNA Transcription Animation • Steps of transcription: 1. Gene is recognized, DNA unwinds 2. RNA strand binds to template strand - G C, T A, A U (not T) 3. Completed RNA strand separates

DNA Translation • Translation- process converts, m. RNA message into a polypeptide – Polypeptides make up proteins • Codon- 3 nucleotide sequence that codes for an amino acid

DNA Translation

Steps of Translation 1. The start m. RNA codon attracts a complimentary t. RNA anticodon 2. Each amino acid is added to the next t. RNA 3. Process continues until a stop codon is reached. 4. Protein is then released

Gene Expression • Genes can make a lot of protein, little, or none • Transcription is controlled by promoters and operators • Promoter- DNA segment that allows a gene to be transcribed • Operator- DNA segment turns a gene “on” or “off”

Gene Expression • Operon– region of DNA that includes a promoter, operator and genes that code for certain proteins

m. RNA Processing • Sometimes pieces of m. RNA are not needed 1. Introns are removed 2. A cap and tail are added 3. Molecule joins together

Mutations • mutation- change in an organism’s DNA • Single gene mutations usually occur in replication • Mutations affecting a group of genes happen in meiosis

Mutations • Types of mutations: 1. Point mutation- one nucleotide is substituted for another 2. Frameshift mutation 1. Insertion- addition of a nucleotide 2. Deletion- removal of a nucleotide 3. Gene duplication 4. Gene translocation

Point mutation Gene duplication Frameshift Translocation