BIOLOGY UNIT 4 STUDY GUIDE

Repressor proteins

Stop gene activity

activator proteins

bind to enhancer sequence and stimulates transcription

Operator sites

Sites where repressors bind.

Enhancer sites

Sites where activators bind.

Polytene chromosome puffs

Indicate active gene transcription due to activation proteins.

mRNA transcript processing controls

(1) Alternative splicing, (2) Poly-A tail length.

Translational controls

(1) RNA degradation, (2) Blocking 5' cap.

Post-translational controls

(1) Allosteric controls, (2) Phosphorylation of proteins.

Operon

Controls the expression of groups of genes together.

Lac operon

High lactose: transcription occurs; promoter is free (repressor binds lactose). Low lactose: blocks transcription; repressor binds promoter.

Restriction enzymes

Cut DNA at a specific sequence.

DNA ligase

Joins 2 DNA strands.

Plasmid

Small circle of bacterial DNA; acts as cloning vector.

Transgenic organism

Organism with genes inserted from another organism.

Example of a transgenic organism

Featherless chicken, goat producing drugs, insulin-producing organisms, etc.

DNA fingerprinting

Cut DNA with restriction enzymes, run DNA on gel electrophoresis; compare banding patterns.

PCR

Rapid technique to make large quantities of a specific DNA sequence.

Gel electrophoresis

Separation of DNA using gel electrophoresis.

Recombinant DNA

DNA used to create transgenic organisms.

CRISPR

Targeted gene editing; replaces one version of a gene with another.

Transcription

Copying DNA segment into mRNA — occurs in the nucleus (eukaryotes).

RNA polymerase

Binds DNA to the promoter for a gene.

Gene promoter

Binding site for RNA.

Stop signal

Nucleotide sequence in mRNA; signals end of protein synthesis.

RNA transcript modifications

1. Capping - adds modified G to start. 2. Splicing - removes introns and joins exons. 3. Polyadenylation - adds adenine (A) tail to end.

Translation

Converts genetic info in mRNA into amino acid sequence to form protein — occurs at ribosomes.

mRNA codons

(Example shown: 5' TAGACATT → mRNA: AU CUGU AA S).

Role of ribosomes & tRNA in translation

Ribosomes read mRNA; tRNA carries correct amino acids to ribosomes.

Base-pair substitutions

One nucleotide base error (wrong amino acid).

Gene insertion or deletion

DNA sequence changes from adding or removing nucleotides.

Frameshift mutations

Gene insertion or deletion.

Mutagen

Any physical or chemical agent that causes permanent change in DNA.

Types of mutagens

Radiation (UV, X-ray), chemicals (tobacco, pesticides), viruses.

Selectively expressed genes

Specific genes are turned on or off.

Methylation of DNA

Transcriptional control; blocks promoter.

Acetylation of DNA

Transcriptional control.

Discovery of Miescher

Isolated nuclear material.

Discovery of Griffith

Isolated 2 strains of Streptococcus pneumoniae.

Discovery of Avery

Treated transforming bacteria.

Discovery of Hershey & Chase

Created/labeled bacteriophages.

Discovery of Watson & Crick

Double helix structure (2 nucleotide strands).

DNA nucleotides

Adenine, Guanine, Thymine, Cytosine.

Characteristics of DNA (Watson & Crick model)

1. Double helix. 2. Strands held by hydrogen bonds. 3. A binds T; G binds C. 4. Strands run in opposite directions. 5. 2 nucleotide strands.

Functions of replication enzymes

• Helicase: Unwinds DNA.- DNA polymerase: Attaches primers; nucleotides in 5'→3' direction.- Ligase: Fills gaps between fragments and connects segments.

Semi-conservative replication

Each DNA strand creates one new complementary strand.

Lagging strand in DNA replication

Okazaki fragments.

Order of events for protein synthesis

DNA transcribed to form RNA; RNA translated to form polypeptides (proteins).

Difference between RNA and DNA

DNA = double-stranded; RNA = single-stranded.

Types of RNA and functions

• rRNA: Makes ribosomes; where translation occurs.- mRNA: Codes for proteins.- tRNA: Transfers amino acids to ribosomes.