Mcat Biology Lecture 3

Front 1

Virus

Back 1

Tiny infectious agents (smaller than bacteria - size of large protein)

Consists of:
1. Capsid
2. DNA or RNA genes

Some surround themselves with a lipid-rich envelope

All organisms experience viral infections

Not considered organisms

Reproduce with host's reproductive machinery (transfer of genetic information)

Do not metabolize organic nutrients, use ATP from host

In active form, not separated from external environment like cell wall or membrane

Possess either DNA or RNA, not both

Can be crystallized without losing ability to infect

Front 2

Capsid

Back 2

Protein coat

Also know as head

Contains nucleic acids
DNA or RNA genes inside

Front 3

Envelope

Back 3

Lipid-rich

Either borrowed from host cell or synthesized in host cell cytoplasm

Contains virus-specific proteins

Front 4

Virion

Back 4

Mature virus outside host cell

Front 5

Host

Back 5

Cell being infected

Front 6

Viral infection

Back 6

Begins when virus absorbs to a specific chemical receptor site on host

1. Landing
2. Attachment
3. Tail contraction
4. Penetration and injection

Most viruses that infect eukaryotes are engulfed via endocytosis

Once inside cell, 2 paths:
1. lysogenic infection
2. lytic infection

Front 7

Chemical receptor

Back 7

Usually specific glycoprotein on host cell membrane

Virus cannot infect cell if specific receptor is not available

Front 8

Bacteriophage

Back 8

Virus that infects bacteria

Made up of:
1. Capsid or head
2. Tail
3. Tail fiber

Nucleic acid is injected through the tail after viral enzymes have digested a hole in the cell wall

Front 9

Lytic infection

Back 9

Virus takes control of host's reproductive machinery and makes new viruses

Front 10

Eclipse period

Back 10

Brief period before first fully formed virion appears

Front 11

Latent period

Back 11

Period from infection to lysis (fill with new viruses until it bursts)

Encompasses the eclipse period

Front 12

Virulent virus

Back 12

Virus following a lytic cycle

Front 13

Lysogenic infection

Back 13

Viral DNA is incorporated into host genome

If RNA, DNA is reverse transcribed from RNA and then incorporated into host genome

When host cell replicates DNA, viral DNA is replicated as well

Temperate virus - host may show no symptoms of infection

Front 14

Reverse transcriptase

Back 14

Enzyme that reverse-transcribes RNA into DNA

Front 15

Dormant or Latent

Back 15

When viral DNA remains incorporated in host DNA - no symptoms

Front 16

Provirus

Back 16

Prophage if virus is in bacterium

Virus that is dormant or latent

Front 17

Virulent

Back 17

When virus is not longer dormant or latent and becomes active

Front 18

Plus-strand RNA

Back 18

Virus that is unenveloped

Ex: common cold

Plus-strand indicates that proteins can be directly translated from RNA

Front 19

Retroviruses

Back 19

Virus with enveloped plus-strand RNA

Ex: HIV/AIDS

Carries reverse-transcriptase enzyme to create DNA from RNA - then DNA is incorporated into host genome

Front 20

Minus-strand RNA

Back 20

Virus with minus-strand RNA

Minus-strand RNA is complement to mRNA and must be transcribed to plus-RNA before being translated

Ex: measles, rabies, flu

Front 21

Types of Viruses:

Back 21

1. Plus-strand RNA
2. Retrovirus
3. Minus-strand RNA
4. Double-stranded RNA
4. Single and double-stranded DNA

Front 22

Viroids

Back 22

Small rings of naked RNA without capsids

Only infect plants

Front 23

Prions

Back 23

Naked proteins that infect animals

Capable of reproducing themselves, without DNA or RNA

Front 24

Virus Lytic Life Cycle

Back 24

1. Uninfected cell
2. Virus absorbs the cell wall
3. Viral nucleic acid injected into cell
4. Replication of active virus
5. Assembly of new viruses
6. Lysis of cell
7. Virions

Front 25

Virus Lysogenic Life Cycle

Back 25

1. Uninfected cell
2. Virus absorbs to cell wall
3. Viral nucleic acid injected into cell
4. Reduction of provirus
5. Viral DNA integrated into chromosome
6. Reproduction of lysogenic bacteria
7. Induction of of provirus to active virus
8. Replication of active virus
9. Assembly of new viruses
10. Lysis of cell
11. Virions

Front 26

Vaccine

Back 26

1. Injection of antibodies
2. Injection of non-pathogenic virus with same capsid or envelope (allows for host immune system to create its own antibodies)

Front 27

How to kill viruses:

Back 27

1. Antibodies to viral proteins (constantly mutating)
2. Cytotoxic T cells which destroy infected cell

Front 28

Carrier population

Back 28

Makes it difficult to fight viral infections

Can infect more than one animal, some animals infected without symptoms

Front 29

Prokaryotes

Back 29

Organisms without membrane bound nucleus

2 domains:
1. Bacteria
2. Archaea

Single, circular double stranded molecule of DNA

Contain a nucleoid

No complex, membrane-bound organelles

Contain RNA, small ribosomes (translating proteins), mesosomes (not necessarily), inclusion bodies, nucleoid, etc.

Front 30

Archaea

Back 30

Much in common with eukaryotes and bacteria

Found in extreme environments (salty lake and boiling hot springs)

Cell wall not made from peptidoglycan (unlike bacteria)

Front 31

Fixing CO2

Back 31

Reducing CO2 and using carbon to create organic molecules

Process called Calvin Cycle

Energy expensive

Front 32

Autotrophs

Back 32

Organisms capable of using CO2 as their sole source of carbon

Front 33

Heterotrophs

Back 33

Organism that use preformed organic molecules as carbon source

Front 34

2 sources of Energy

Back 34

1. Light
2. Oxidation of organic or inorganic matter

Front 35

Phototrophs

Back 35

Organisms that use light as energy source

Front 36

Chemotrophs

Back 36

Organisms that use oxidation of organic or inorganic matter as energy source

Only prokaryotes can acquire energy from inorganic source other than light

Front 37

Nucleoid

Back 37

DNA, RNA and protein complex in prokaryotes

Forms a structure that is visible under light microscope

Also called: chromatin body, nuclear region or nuclear body

Not enclosed by membrane

Front 38

2 types of bacteria

Back 38

1. cocci (round)
2. bacilli (rod shaped)
3. Spirilla (helically shaped, rigid)
4. Spirochetes (helically shaped, not rigid)

Front 39

Plasma membrane

Back 39

phospholipid bilayer surrounding cytosol of prokaryotes

Front 40

Phospholipid

Back 40

composed of:
1. phosphate group (polar)
2. 2 fatty acid chains (nonpolar)
3. glycerol (3C backbone)

amphipathic: having both polar and nonpolar portions - molecules spontaneously aggregate in aqueous solution, turning polar ends toward solution and nonpolar ends towards each other - making a spherical structure)

Front 41

Micelle

Back 41

Spherical structure formed by amphipathic molecules in aqueous solution

Front 42

Membrane proteins

Back 42

1. Transporters
2. Receptors
3. Attachment sites
4. Enzymes

Functional aspects of membranes

Front 43

Integral or Intrinsic Proteins

Back 43

Amphipathic proteins that traverse membrane from inside of cell to outside of cell

Front 44

Peripheral or Extrinsic Proteins

Back 44

Proteins entirely on surface of membrane

Ionically bonded to integral proteins or polar group of lipid

Front 45

Fluid Mosaic Model

Back 45

Model of membrane fluidity

Membrane is held together by intermolecular forces

Membrane is fluid - its parts can move laterally but cannot separate

Assymetrical layout of membrane proteins (mosaic aspect of membrane)

Haponoids (steroid-like molecules in prokaryotes) or steroids (eukaryotes) reduce fluidity of membrane

Front 46

Diffusion

Back 46

Movement of compound in high concentration to low concentration (for molecules without electric charge)

Occurs in direction of decreasing free energy or increasing universal entropy

Front 47

Chemical concentration gradient

Back 47

Gradual change in concentration of compound over a distance

Series of vectors pointing toward lower concentration

Front 48

Electrical gradient

Back 48

Movement of compound with charge

Points in direction that positively charged particle will tend to move (toward negative charge)

Front 49

Electrochemical gradient

Back 49

Combination of electrical and chemical gradient for a specific compound

Front 50

Semipermeable

Back 50

Membrane slows but does not stop diffusion of compound

Affected by:
1. Size
2. Polarity

The larger the molecule, the less permeable the membrane to that molecule

The more polar a molecule, the less permeable the membrane to that molecule

Front 51

Passive diffusion

Back 51

Diffusion of molecules through leakage channels across membrane due to random motion

Front 52

Transport or Carrier Proteins

Back 52

Designed to facilitate diffusion of specific molecules across the membrane

Molecules that are too large or too charged

Front 53

Facilitated Diffusion

Back 53

Diffusion must occur down the electrochemical gradient of all compound involved

Many mechanisms used by transport proteins

Ex: glucose

Makes membrane selectively permeable - able to select between molecules of similar size and charge

Front 54

Active transport

Back 54

Movement of compound against electrochemical gradient in order to concentrate nutrients

Requires expenditure of energy:
1. Direct expenditure of ATP
2. Using ATP to create an electrochemical gradient, using energy of electrochemical gradient to expel or acquire compound of interest (Secondary active transport)

Front 55

Protoplast

Back 55

Bacterial plasma membrane and everything inside it

Not a complete bacterium

Surrounded by bacterial envelope

Front 56

Bacterial envelope

Back 56

Component of envelope, adjacent to plasma membrane is the cell wall

Front 57

Cell Wall

Back 57

Prevent protoplast from bursting

Front 58

Hypertonic

Back 58

Aqueous solution of cytosol contains more particles than surrounding aqueous solution

property of bacteria

Front 59

Isotonic

Back 59

Cytosol contains same amount of particles as surrounding aqueous solution

Front 60

Hypotonic

Back 60

Cytosol contains less particles than surrounding aqueous solution

Front 61

Hydrostatic pressure

Back 61

Pressure created by cell wall filling with water

Equal to osmotic pressure when at equilibrium

Front 62

Peptidoglycan

Back 62

Makes up cell wall

Archaea do not have

Series of disaccharide polymer chains with amino acids (3 of which are not found in proteins)

Form single molecular sac around bacterium

More elastic than cellulose

Porous - allows large molecules to pass through

Front 63

Gram staining

Back 63

Classification of bacteria based on type of cell wall

Front 64

Gram-positive bacteria

Back 64

Thick peptidoglycan cell wall (4x thicker than plasma membrane) prevents gram stain from leaking out

Cells stain purple

Front 65

Gram-negative bacteria

Back 65

Appear pink when stained

Thin peptidoglycan cell wall allows gram stain to wash off

Have phospholipid bilayer (more permeable - allowing large molecules, like glucose, to pass through) outside cell wall

Front 66

Gram-positive envelope

Back 66

1. Capsule
2. Peptidoglycan
3. Periplasmic space
4. Plasma membrane
5. Cytosol

Front 67

Gram-negative envelope

Back 67

1. Capsule
2. Lipsaccharide layer
3. Outer membrane
4. Periplasmic space
5. Peptidoglycan
6. Periplasmic space
7. Plasma membrane
8. Cytosol

Front 68

Bacterial Flagella

Back 68

Long, hollow, rigid, helical cylinders

Made from globular protein called flagellin

Not same as eukaryotic flagella (made of microtubules)

Rotate counterclockwise to propel bacterium in single direction

If rotate clockwise, bacterium tumbles, allowing bacterium to change directions

Uses energy from proton gradient (not ATP)

Front 69

Flagellin

Back 69

Globular protein that makes flagella

Front 70

Genetic Recombination

Back 70

1. Conjugation
2. Transformation
3. Transduction

Not mechanism of reproduction

Front 71

Binary Fission

Back 71

Mechanism of asexual reproduction of bacterium

1. Circular DNA is replicated
2. Form 2 complete DNA double stranded circles
3. Cell divides, leaving one circular chromosome in each cell

2 daughter cells are genetically identical

Front 72

Conjugation

Back 72

Type of genetic recombination

1 of bacterium requires a plasmid with gene coding for sex pilus

Sex pilus connects 2 bacteria

Passage of DNA is from cell containing sex pilus to cell cell that does not

Front 73

Plasmids

Back 73

Small circles of DNA that exist and replicate independently of bacterial chromosome

Replicates differently than circular chromosome

Front 74

Sex pilus

Back 74

Hollow, protein tube that connect 2 bacteria to allow passage of DNA

Front 75

F plasmid

Back 75

Fertility factor or F factor

1st plasmid to be described

Bacterium with F plasmid = F+
Bacterium without F plasmid = F-

Front 76

R plasmid

Back 76

Donates resistance to certain antibiotics

Conjugative plasmid

Front 77

Transformation

Back 77

Process by which bacteria may incorporate DNA from external environment into genome

Front 78

Transduction

Back 78

Capsid of bacteriophage will mistakenly encapsulate a DNA fragment of host cell

When these virions infect new bacterium, they inject harmless bacterial DNA fragments instead of virulent viral DNA fragments

Front 79

Vector

Back 79

Virus that mediates transduction

Front 80

Fungi

Back 80

Distinct kingdom of organisms with diversity

Eukaryotic heterotrophs

Obtain food by absorption rather than ingestion

Secrete digestive enzymes outside bodies and absorb products of digestion

Most are saprophytic

Most posses septa

Fungal cell may contain 1 or more nuclei (mitosis takes place entirely within the nucleus)

Consist of mycelium of hyphae

Multicellular (exception Yeast)

Lack centrioles

Front 81

Saprophytic

Back 81

Live off dead organic matter

Front 82

Septa

Back 82

Cell walls of fungi

Made up of polysaccharide chitin

Perforated to allow exchange of cytoplasm between cells (cytoplasmic streaming - allows for rapid growth)

Front 83

Chitin

Back 83

Polysaccharide that makes up cell wall of fungi

More resistant to microbial attack than cellulose

Front 84

Mycelium

Back 84

Tangle mass of hyphae in fungi during growth state

Front 85

Hyphae

Back 85

Multiple thread-like structures making up mycelium in fungi during growth state

Front 86

Haploid

Back 86

single copy of DNA

Predominates in fungi life cycle

Growth stage of fungi

Hyphae are haploid

Front 87

Spores

Back 87

Haploid

Give rise to new mycelia in asexual reproduction

Borne by air currents, water or animals

Front 88

Budding

Back 88

Asexual reproduction in yeast

Also called cell fission

Smaller cell pinches off from single parent cell

Front 89

Sexual reproduction in fungi

Back 89

Between hyphae from 2 mycelia of different mating types (+ and -)

1. 2 hyphae grow towards one another
2. Touch
3. Form conjugation bridge
4. Tip of hyphae forms complete septum
5. Becomes gamete producing cell
6. Gametes fuse into zygote (diploid)

Asexual reproduction occurs when conditions are good

Sexual reproduction occurs when conditions are tough