MBIO - Course 2

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What is genetics?

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What is genetics?

Study of heredity

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What is molecular biology?

Study of DNA and protein synth

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What is a genome?

Total DNA in a cell (chromosomes & plasmids)

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What are genes?

Sections of DNA that code for traits

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What is a DNA?

Macromolecule made of nucleotides

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What does each DNA nucleotide consist of?

N base, deoxyribose sugar, phosphate

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What shape is DNA?

Double helix

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What is the base pairing rule?

A - T, C - G

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How are nucleotides linked together?

Phosphodiester bonds

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What is the flow of genetic information?

  1. Replication

  2. Gene expression

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

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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

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What is the leading strand?

The strand that follows the replication fork

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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

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What are the parts of gene expression?

  1. Transcription

  2. Translation

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What are the 3 types of RNA?

  1. mRNA

  2. rRNA

  3. tRNA

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What is the first step in transcription?

RNA polymerase bond to promoter and copies the template strand

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What is the second step in transcription?

As RNA polymerase synthesizes new RNA, DNA rewinds behind it

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What happens during the third step in transcription?

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

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What are codons?

Set of 3 nucleotides

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What does mRNA do?

Info from DNA used to make proteins

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What are stop codons?

UAA, UAG, UGA; signals end of protein synth

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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

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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

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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

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How does genetic change happen in bacteria?

Mutation and horizontal gene transfer

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What is mutation?

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

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What is horizontal gene transfer?

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

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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)

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What is frameshift mutation?

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

  • Non-functional protein

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How do mutations happen?

Spontaneous or induced mutations

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What is spontaneous mutation?

Happens in absence of mutagens because of mistakes during DNA replication

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What is induced mutation?

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

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What is silent mutation?

No effect on protein - remaining functional

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What is missense mutation?

Protein with a different amino acid sequence w/ dif function

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What is nonsense mutation?

Incomplete protein because of early stop codon

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What are plasmids?

Self replicating DNA molecules that have non-essential genes

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What are F Plasmids?

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

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What is conjugation?

Transfer of gene material between bacteria

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What are R plasmids?

Resistance factors - Genes for antibiotic resistance

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What are Vir plasmids?

Virulence factors - Genes for toxin production

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What are the steps in horizontal gene transfer?

  1. Transformation

  2. Transduction

  3. Conjugation

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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

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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

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What are transducing particles?

Bacteria DNA instead of phage DNA in newly made phages

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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+)

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What are viruses?

Acellular microbes that can infect and cause disease in host cells

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Why do viruses need hosts?

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

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What are some features that viruses have?

  • No plasma membrane

  • DNA or RNA with protein coat

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What are viruses’ host range?

Most are single host species specific

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What structures make up a virus?

  • Nucleic acid

  • Capsid

  • Envelope

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What are capsids?

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

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What does the viruses’ envelope consist of?

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

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What are the morphology of viruses?

  • Polyhedral

  • Helical

  • Enveloped

  • Complex

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Describe the polyhedral shape of viruses

Icosahedral - shape with 20 triangular faces

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Describe the helical shape of viruses

Long rods that can be rigid and flexible

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Describe the enveloped shape of viruses

Roughly spherical

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Describe the complex shape of viruses

Polyhedral head w/ helical tail; only in bacteriophages

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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

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What is the naming structure of viruses?

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

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Process of animal virus multiplication

  1. Adsorption

  2. Penetration

  3. Uncoating

  4. Biosynthesis

  5. Maturation & Assembly

  6. Release

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What happens during adsorption?

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

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What happens during penetration?

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

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What happens during uncoating?

Viral nucleic acid freed from capsid

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What happens during biosynthesis?

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

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What happens during maturation and assembly?

New virions assembled:

  • Capsid → Capsomeres

  • Nucleic acid enter capsid → Nucleocapsid

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What happens during release?

  • Naked: Burst out → host cell dies

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

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What are the different types of infections?

  • Acute

  • Persistent viral

  • Chronic viral

  • Latent viral

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What is an acute infection?

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

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

Measles → subacute sclerosing panencephalitis

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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

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What is a chronic viral infection?

After acute, virus remains with maybe no noticeable symptoms

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What is a latent viral infection?

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

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What is a provirus?

Virus that’s integrated into DNA of host cell

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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

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What is a tumor?

Abnormal growth of tissue

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What is a benign tumor?

A tumor that doesn’t spread

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What is a malignant tumor?

Tumor that metastasize and invade nearby tissue (cancer)

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Which genes control cell growth?

  • Proto-oncogenes

  • Tumor suppressor genes

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What is a proto-oncogene?

Gene that stimulates cell growth

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What is a tumor suppressor gene?

Gene that inhibit cell growth

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What leads to tumor formation and cancer?

Mutations in proto-oncogene or tumor suppressor gene

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What are oncogenes?

Genes that alter cell’s control mechanisms

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What does Hepatitis B and C cause?

Liver cancer

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What does the Epstein-Barr virus cause?

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

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