MBIO - Course 2

What is genetics?

Study of heredity

What is molecular biology?

Study of DNA and protein synth

What is a genome?

Total DNA in a cell (chromosomes & plasmids)

What are genes?

Sections of DNA that code for traits

What is a DNA?

Macromolecule made of nucleotides

What does each DNA nucleotide consist of?

N base, deoxyribose sugar, phosphate

What shape is DNA?

Double helix

What is the base pairing rule?

A - T, C - G

How are nucleotides linked together?

Phosphodiester bonds

What is the flow of genetic information?

1. Replication

2. Gene expression

   1. Recombination (DNA flow between 2 dif bacterial cells)

What happens during DNA replication?

Helicase unzips DNA while primase produces RNA primer, marking a start point for DNA polymerase to read each strand and create a complementary strand

What is the leading strand?

The strand that follows the replication fork

What is the lagging strand?

The strand that goes away from the replication fork; creates Okazaki fragments that is joined together by DNA ligase afterwards

What are the parts of gene expression?

1. Transcription

2. Translation

What are the 3 types of RNA?

1. mRNA

2. rRNA

3. tRNA

What is the first step in transcription?

RNA polymerase bond to promoter and copies the template strand

What is the second step in transcription?

As RNA polymerase synthesizes new RNA, DNA rewinds behind it

What happens during the third step in transcription?

RNA polymerase hits terminator, making it drop the newly synth RNA strand

What are codons?

Set of 3 nucleotides

What does mRNA do?

Info from DNA used to make proteins

What are stop codons?

UAA, UAG, UGA; signals end of protein synth

What happens in the first step of translation?

Ribosome assembles on mRNA; F-Met enters P-site, then next amino acid based on codons in A-site enters and F-Met binds to it using peptide bonds

What happens in the second step of translation?

Ribosome goes done mRNA, adding corresponding amino acids based on codons in A-site to the growing polypeptide chain in P-site, and releasing used tRNA at the E-site

• Continues until stop codon

What happens in the third step in translation?

Ribosomes disassemble and releases polypeptide which then folds into its shape and becomes a protein

• Disassembled ribosomes can be used again

How does genetic change happen in bacteria?

Mutation and horizontal gene transfer

What is mutation?

Change in nucleotide sequence of DNA which may change the original protein

What is horizontal gene transfer?

Gene info passed from one cell to another from the same gen

What is base substitution?

Single nucleotide is replaced by another, resulting in a base pair when DNA replicates

• Missense mutation after translation (incorrect amino acid in protein)

What is frameshift mutation?

Insertion/Deletion of 1 or 2 nucleotides, changing reading frame of mRNA

• Non-functional protein

How do mutations happen?

Spontaneous or induced mutations

What is spontaneous mutation?

Happens in absence of mutagens because of mistakes during DNA replication

What is induced mutation?

Happens because of mutagens - damages DNA and causes changes in its sequence

What is silent mutation?

No effect on protein - remaining functional

What is missense mutation?

Protein with a different amino acid sequence w/ dif function

What is nonsense mutation?

Incomplete protein because of early stop codon

What are plasmids?

Self replicating DNA molecules that have non-essential genes

What are F Plasmids?

Fertility factors - carry gene to make F pilus (sex factor) which is involved in conjugation

What is conjugation?

Transfer of gene material between bacteria

What are R plasmids?

Resistance factors - Genes for antibiotic resistance

What are Vir plasmids?

Virulence factors - Genes for toxin production

What are the steps in horizontal gene transfer?

1. Transformation

2. Transduction

3. Conjugation

What happens during the first step of horizontal gene transfer?

Pieces of “naked” DNA taken up by bacterial cell

• Can be integrated into chromosome for recombination

What happens in the second step of horizontal gene transfer?

Fragments of DNA transfer between bacteria thru bacteriophage which attaches to the cell wall - injecting DNA inside so that phage DNA can replicate inside

• Chance of transducing particles which can pass to another cell

What are transducing particles?

Bacteria DNA instead of phage DNA in newly made phages

What happens in the third step of horizontal gene transfer?

Transfer happens when donor (F+) cell forms F pilus to attach to recipient (F-) cell; Recipient cell becomes (F+)

What are viruses?

Acellular microbes that can infect and cause disease in host cells

Why do viruses need hosts?

Requires the host cell’s metabolic system to multiply, disrupting host’s normal function

What are some features that viruses have?

• No plasma membrane

• DNA or RNA with protein coat

What are viruses’ host range?

Most are single host species specific

What structures make up a virus?

• Nucleic acid

• Capsid

• Envelope

What are capsids?

Protein coat that surround nucleic acid that is made up of capsomeres

What does the viruses’ envelope consist of?

Lipid bilayer from the host cell with spikes (viral proteins) inserted in it

What are the morphology of viruses?

• Polyhedral

• Helical

• Enveloped

• Complex

Describe the polyhedral shape of viruses

Icosahedral - shape with 20 triangular faces

Describe the helical shape of viruses

Long rods that can be rigid and flexible

Describe the enveloped shape of viruses

Roughly spherical

Describe the complex shape of viruses

Polyhedral head w/ helical tail; only in bacteriophages

Classification of viruses

1. Nucleic acid type

   • DNA or RNA

   • Single or double stranded

   • Segmented or single

2. Capsid structure

   • Polyhedral

   • Helical

3. Presence of envelope

What is the naming structure of viruses?

Family ends with -viridae; Genus ends with -virus; Descriptive name instead for species

Process of animal virus multiplication

1. Adsorption

2. Penetration

3. Uncoating

4. Biosynthesis

5. Maturation & Assembly

6. Release

What happens during adsorption?

Attach to host cell - virus attachment sites recognize protein/glycoprotein of host membrane

What happens during penetration?

Entry into host - enveloped viruses enter thru fusion, naked enter thru endocytosis

What happens during uncoating?

Viral nucleic acid freed from capsid

What happens during biosynthesis?

Viral nucleic acid replicated (DNA in nucleus, RNA in cytoplasm), viral proteins (capsomeres) synth in cytoplasm

What happens during maturation and assembly?

New virions assembled:

• Capsid → Capsomeres

• Nucleic acid enter capsid → Nucleocapsid

What happens during release?

• Naked: Burst out → host cell dies

• Enveloped: Bud out → host cell lives and steadily releases more

What are the different types of infections?

• Acute

• Persistent viral

• Chronic viral

• Latent viral

What is an acute infection?

Result from tissue damage, short, host may have long immunity

What is an example of an acute infection with late complications?

Measles → subacute sclerosing panencephalitis

What is a persistent viral infection?

Infection where virus is present with maybe no symptoms

• Host can act as reservoir and transmit virus to others

What is a chronic viral infection?

After acute, virus remains with maybe no noticeable symptoms

What is a latent viral infection?

Acute with symptomless period; virus gives copy of DNA into host and remain dormant until reactivation years later

What is a provirus?

Virus that’s integrated into DNA of host cell

What is an example of a latent viral infection?

Varicella-Zoster virus (herpes) which causes chicken pox in children and can be reactivated later and cause shingles

What is a tumor?

Abnormal growth of tissue

What is a benign tumor?

A tumor that doesn’t spread

What is a malignant tumor?

Tumor that metastasize and invade nearby tissue (cancer)

Which genes control cell growth?

• Proto-oncogenes

• Tumor suppressor genes

What is a proto-oncogene?

Gene that stimulates cell growth

What is a tumor suppressor gene?

Gene that inhibit cell growth

What leads to tumor formation and cancer?

Mutations in proto-oncogene or tumor suppressor gene

What are oncogenes?

Genes that alter cell’s control mechanisms

What does Hepatitis B and C cause?

Liver cancer

What does the Epstein-Barr virus cause?

Infectious mononucleosis; may cause cancers of WBC (lymphoma) and of nose and throat

What does the Human Papillomavirus (HPV) cause?

Genital warts and cervical cancer

What are viroids?

Naked RNA w/o protein coat

• Cause disease in plants

What are prions?

Infection protein particles w/o gene material that’s linked to human and animal diseases

What are the modes of infection?

Through food: destroyed at 480*C or autoclave in SOH-

What is innate immunity?

Immunity you’re born with; non-specific, no memory, and always present which means it responds fast

What defenses does innate immunity have?

First line defense (phys & chem barriers to prevent entry) and second line defense (eliminate microbe from body)

What are the physical barriers?

Skin, mucous membrane, fluid flow

What is the job of the skin?

Frequently sheds (remove microbes), dry (inhibit growth), rarely penetrated by microbes

What is the job of the mucous membrane?

Fluid/gas exchange, lines tracts and secrete mucous (glycoprotein) that traps microbes and cilia sweep it away

What is the job of fluid flow?

Bodily secretions that moves microbes away from the body

What are the chemical barriers?

Acidity of body fluids & skin, lysozome, lactoferrin, defensins, and normal microbiotaW

What is the job of acidity of body fluids and skin?

• Stomach acid (pH 2) destroys bacteria & toxins

• Skin fatty acid & lactic acid (pH 3-5) prevent growth

What is the job of lysozome?

Degrades peptidoglycan

What is the job of lactoferrin?

Iron binding proteins in mill & mucous that makes it slow microbe growth

What are the jobs of defensins?

Short polypeptide that poke holes in membranes

• produced by epithelial cells

What are the jobs of normal microbiota?

Prevents growth of pathogens thru comp exclusion & microbial antagonism