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

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.mRNA- message 2.rRNA- forms part of ribosomes 3.tRNA- transfers amino acids to help make proteins

DNA Transcription 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 Transcription Animation

DNA Translation Translation- process converts, mRNA 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 mRNA codon attracts a complimentary tRNA anticodon 2.Each amino acid is added to the next tRNA 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

mRNA Processing Sometimes pieces of mRNA 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