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 – CytosinePyrimidines

• 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 unzipped2. Free nucleotides bind to each template

strand3. 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- message2. rRNA- forms part of ribosomes3. tRNA- transfers amino acids to help make

proteins

DNA Transcription

• Steps of transcription:1. Gene is recognized, DNA unwinds2. RNA strand binds to template strand

- GC, TA, AU (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 Translation1. 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 removed2. A cap and tail are

added3. 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

another2. Frameshift mutation

1. Insertion- addition of a nucleotide2. Deletion- removal of a nucleotide

3. Gene duplication4. Gene translocation

Point mutation Gene duplication

Frameshift

Translocation