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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