UNIT 3 BIO

How are the components of DNA organized?

DNA is a polymer (many repeating units) and each unit is called a nucleotide

Double helix structure, with two strands of nucleotides linked by hydrogen bonds

What does DNA helicase do?

It is a protein that goes to the site of replication and unwinds the double helix by breaking hydrogen bonds that hold the complementary bases together.

What does DNA polymerase III do? How does it synthesize DNA?

• Used to build a new complementary strand

• Synthesizes DNA by adding free floating deoxyribonucleoside triphosphates (dNTPs)

Transcription

Information found in DNA is copied in the form of a single stranded nucleic acid called mRNA

Translation

• Ribosomes use the mRNA as a blueprint to make protein

• Occurs in our DNA code

What is a promoter and what does it do?

A specific site on the DNA where the enzyme RNA polymerase binds, upstream of the gene to be transcribed, and unzips it.

What is the function of tRNA in protein synthesis?

Matching amino acids with their corresponding codons in mRNA

Lac operon

• Activated when lactose is present (high levels induce the operon)

• Lacl repressor protein binds to the operator when lactose levels are low

Trp operon

• Normally active, but deactivated when Trp is high (high levels repress the operon)

• Trp repressor protein binds to the operator when tryptophan levels are high

Silent mutations

No effect on cell operation, usually occur in non-coding regions of DNA and are very common

Missense mutations

A codon is altered, resulting in a different amino acid being included in the protein sequence

Nonsense mutations

• A change in the DNA sequence causes a stop codon to occur too early

• Harmful to the cell because a large part of the protein might not be made

Translocation mutations

• involve errors in the overall chromosomes

• A segment of DNA attaches to a non-homologous chromosome (a different chromosome, not part of the pair)

What can cause mutations?

1. Errors in genetic machinery

2. Point mutations

3. Exposure to mutagenic agents

Restriction endonucleases definition

Restriction enzymes

Allow DNA to be cut at specific base pair sequences

Sticky vs blunt ends

Sticky - overhangs left on the DNA when cut (makes them easier to rejoin)

Blunt - DNA strands separate but there is no overhang

What are methylases and how do they work?

• Enzymes that protect DNA from restriction enzyme cutting

• Put methyl groups on certain bases at the recognition site which protects it from being destroyed

Explain the 3 cycles of PCR

1. Denaturation - double stranded DNA are heated to separate the strands

2. Annealing - primers bind to flanking regions of DNA

3. Extension - DNA polymerase extends the end of each primer along the template strands

   • these steps are repeated to exponentially produce exact copies of the target DNA

What do restriction enzymes do?

• RFLP can detect differences in DNA sequences based on restriction enzyme cutting sites

• DNA is digested with a particular restriction enzyme. The pieces are then put through a gel and the segments are seen as a bonding pattern in the gel

Outcome of RFLP analysis?

A unique blotting pattern characteristic to a specific genotype

Can be used to match suspect’s DNA or detect genetic disorders