Lecture 8 - DNA Structure

What are three needed characteristics for hereditary material

1. A code that can be expressed - has genotypic instructions for phenotype

2. A code that can be replicated accurately so genotype is successfully passed to new cells

3. SMALL amount of error to allow mutations/evolution to occur → generates new traits (deleterious and beneficial)

Bacterial colonies

Clones of thousands of bacterial cells

IIIS Virulent

Contains a polysaccharide capsule

IIR Nonvirulent

Does NOT contain a polysaccharide capsule

Describe Griffith’s experiment

Demonstrated bacterial transformation where non-virulent bacteria turned virulent upon exposure to heat killed virulent straints

What are the results from Griffith’s experiments?

• IIIS boiled → no death

• IIR → no death

• IIR + IIIS boiled → DEATH

What did Avery, MacLeod, and McCarty’s experiments prove?

The transforming agent in DNA samples from heat killed IIIS CANNOT be destroyed by proteases or RNAses, BUT can be destroyed by DNAse → Contaminants (RNA and protein) in DNA are NOT responsible for tranforming nonvirulent bacteria into virulent bacteria

What did the Hershey and Chase bacteriopgage experiment prove?

DNA is the genetic material and NOT protein

DNA is responsible for replication and propagation of bacteriophages

What are three basic components of nucleotides?

Phosphates, deoxyribose, bases

Purine

double ring

Pyrimidine

single ring

nucleoside

base, ribose, NO phosphate

What are four characteristics of DNA

• double helix

• antiparallel

• complimentary base pairing

• can unzip to form a template for replication

What are three things that DNA’s structure tells us?

1. Genetic information can be carried in the base sequences (genetic code)

2. Complementary base pairing is its copy mechanism

3. Changes in information can be due to copy errors → Mutation

Gel electrophoresis

A lab technique that is used to separate mixtures of biological molecules based on their physical properties

• Can be used to estimate the length of DNA

What does the number of different sized DNA molecules correspond with?

The number of chromosomes

What is the relationship between DNA length and organismal complexity?

• Chromosome number does NOT correspond with organismal complexity

• Genome size tends to increase with organismal complexity. Some simple organisms have larger genomes than mammals