Weeks 8–10 Bacterial Genetics, Genetic Engineering, and Virus Key Concepts

Protein functions

Enzymes, structure, transport, signaling, defense, toxins, antibodies

Gene

Segment of DNA encoding a protein or functional RNA

Gene expression

Transcription + translation to produce gene products

Transcription

Using DNA template to synthesize RNA by RNA polymerase

Translation

Using mRNA to build protein at ribosome

DNA polymerase

Adds nucleotides to growing DNA strand, proofreads

Primase

Makes RNA primers for DNA replication

Helicase

Unwinds DNA at replication fork

Ligase

Seals Okazaki fragments on lagging strand

Topoisomerase / Gyrase

Relieves supercoiling/tension in DNA

Leading strand

Synthesized continuously toward fork

Lagging strand

Synthesized in fragments (Okazaki) away from fork

Okazaki fragments

Short DNA segments on lagging strand

Origin of replication

Where DNA replication begins

Genome

All DNA in an organism

Promoter

DNA region where RNA polymerase binds

Operon

Group of genes regulated together in prokaryotes

Inducer

Substance that turns ON gene expression

Repressor

Protein that blocks transcription

lac operon

Inducible; ON when lactose present & glucose low

trp operon

Repressible; OFF when tryptophan present

β-galactosidase / permease / transacetylase

Lac operon enzyme products

Mutation

Change in DNA sequence

Missense mutation

Changes single amino acid

Silent mutation

No amino acid change

Nonsense mutation

Stop codon introduced → truncated protein

Frameshift mutation

Addition/deletion not in 3s → shifted reading frame

UV damage

Thymine dimers; repaired by nucleotide excision

Ames test

Detects mutagens using histidine-dependent Salmonella

Horizontal gene transfer

Movement of DNA between bacteria

Transformation

Uptake of naked DNA from environment

Conjugation

Plasmid transfer via sex pilus

Transduction

Phage-mediated DNA transfer

F+ cell

Has F plasmid; donor in conjugation

F- cell

Recipient cell

Hfr cell

F plasmid integrated in chromosome → transfers chromosomal DNA

R plasmid / R factor

Antibiotic resistance plasmid

Bacteriophage

Virus that infects bacteria

Plasmid

Extra-chromosomal circular DNA in bacteria

Generation time

Time it takes population to double

Central dogma

DNA → RNA → Protein

Virus definition

Obligate intracellular parasite; requires host machinery

Virion

Complete infectious viral particle

Genome (virus)

DNA or RNA, single or double-stranded

Capsid

Protein coat around genome

Capsomere

Protein subunit of capsid

Envelope

Outer lipid membrane (only in some viruses)

Spikes

Surface proteins for attachment/entry

Helical virus

Rod-shaped capsid

Polyhedral virus

Many-sided; usually icosahedral

Enveloped virus

Envelope-covered capsid

Complex virus

Structure with head/tail (e.g., phage)

Plaque method

Phage infect bacteria → clear zones = PFU

PFU

Plaque forming units (measures phage)

Attachment

Virus binds host cell receptors

Penetration

Genome enters host

Biosynthesis

Viral nucleic acid & proteins produced

Maturation

Assembly of virions

Release

Lysis or budding of virions

Lysogenic cycle

Phage integrates into host DNA as prophage

Prophage

Phage DNA integrated in bacteria chromosome

Lysogenic conversion

Virus adds new trait to bacteria (e.g., diphtheria toxin)

+ssRNA virus

Genome acts as mRNA

-ssRNA virus

Must synthesize +RNA first

dsRNA virus

Uses viral polymerase to copy genome

Reverse transcriptase

Makes DNA from RNA

Provirus

Viral DNA permanently integrated in host genome

HIV replication

Fusion → reverse transcription → integration → assembly → budding

Oncogenic virus

Virus that can cause cancer

Prion

Infectious misfolded protein causing neurodegeneration

Viroid

Infectious RNA (plants only)

DNA vs RNA

DNA double-stranded, thymine; RNA single-stranded, uracil

Genotype vs phenotype

Genotype = genetic makeup; phenotype = expressed traits

Gene vs chromosome

Gene = sequence encoding product; chromosome = DNA molecule with many genes

Replication vs transcription vs translation

Replication = DNA copy; transcription = DNA→RNA; translation = RNA→protein

Haploid vs diploid

1 chromosome set vs 2 sets

mRNA vs rRNA vs tRNA

mRNA = template; rRNA = ribosome; tRNA = amino acid carrier

Spontaneous vs induced mutation

Natural vs caused by mutagens

Codon vs anticodon

mRNA triplet vs tRNA complement

Lysogeny vs latency

Bacteria vs animal cell genome dormancy

Naked vs enveloped virus

Naked = no envelope, hardy; Enveloped = lipid coated, uses fusion/entry

Lytic vs temperate phage

Immediate lysis vs lysogenic first

Productive vs latent infection

Active virion production vs dormant

ss vs ds nucleic acid

Single vs double strand

CJD vs Mad cow vs CWD

All prion diseases; human vs cow vs deer

DNA vs RNA oncogenic viruses

DNA viruses integrate near growth genes; RNA (retroviruses) carry oncogenes

Bacteriophage vs animal virus

Infect bacteria vs infect eukaryotic cells