Ch 3: Cell Structure and Function

Question 1

Describe prokaryotes

Answer 1

generally small (0.2 - 2 microns diameter & 2-8 microns length)

Include bacteria and archaebacteria

no nucleus or other membrane-bound organelles

one circular chromosome (most)

no histone proteins associated with DNA

cell wall generally contains peptidoglycan (complex polysaccharide) (protein and sugar)

divide by binary fission

Question 2

Describe Eukaryotes

Answer 2

large cells (10–100 µm in diameter)

“true nucleus” and other membrane-bound organelles

multiple linear chromosomes

histone proteins always associated with DNA

cell wall does not contains peptidoglycan

divide by mitosis (complex process that requires a nucleus) (nuclear division, not cell division)

Include algae, protozoa, fungi, animals, and plants

Question 3

Name for sphere shaped bacteria

Answer 3

Coccus

Question 4

Name for rod shaped bacteria

Answer 4

Bacillus

Question 5

Name for very short rod (egg) shaped bacteria

Answer 5

Coccobacillus

Question 6

Name for comma (banana) shaped bacteria

Answer 6

Vibrio

Question 7

Name for spiral shaped & rigid bacteria

Answer 7

Spirillium

Question 8

Name for spiral shaped & flexible bacteria

Answer 8

Spirochete

Question 9

Name for star-shaped bacteria

Answer 9

example: Stella

Question 10

Name for rectangular bacteria

Answer 10

example Haloarcula

Question 11

Bacterial Structure: Glycocalyx

Answer 11

AKA: sugar halo, capsule, or slime layer.
A protective capsule secreted by the cell. This often has the appearance and texture of a ‘slime coating’
Impairs phagocytosis
Impairs antibody binding
Adhesion

Question 12

Bacterial Structure: Pilus

Answer 12

AKA Conjugation tube or sex pilus

Transfer tube which allow movement of plasmid DNA from one bacterium to another (horizontal evolution)

Question 13

Bacterial Structure: Fimbria

Answer 13

attachment filament used to adhere to target cell

Some archaea have fimbriae and hami (s. hamus) (grapling hook)

Question 14

Bacterial Structure: Flagellum

Answer 14

Long, whip-like structure seen in some bacteria that propel cells through their environment

Question 15

Bacterial Structure: Plasmid

Answer 15

Extrachromosomal loop of DNA

Resistant genes

Question 16

Flagellar Arrangements: Who rarely has flagella?

Answer 16

Cocci

Question 17

Flagellar Arrangements: single flagellum located at the pole (end)

Answer 17

Monotrichous

Question 18

Flagellar Arrangements: multiple flagella located at one end

Answer 18

Lophitrichous

Question 19

Flagellar Arrangements: flagella located at both ends

Answer 19

Amphitrichous

Question 20

Flagellar Arrangements: flagella scattered over entire surface

Answer 20

Peritrichous

Question 21

Flagellar Arrangements: without flagella

Answer 21

Atrichous

Question 22

How do bacteria move in response to stimuli? (short answer)

Answer 22

Chemotaxis – movement toward favorable chemicals such as nutrients (positive chemotaxis) or away from harmful chemicals (negative chemotaxis)

Phototaxis – movement toward (or away from) light

Attractant – a positive stimulus which attracts bacteria

Repellent – a negative stimulus that bacteria avoid

Question 23

Describe axial filament

Answer 23

AKA endoflagellum
Wrap around some spiral-shaped bacteria

Contraction of these filaments produces a corkscrew-like motion of these bacteria

Question 24

Describe bacterial cell walls

What is its purpose and what is it composed of?

Answer 24

Provide structure and shape and protect cell from osmotic forces
Assist some cells in attaching to other cells or in resisting antimicrobial drugs
Destroyed with antibiotics
Give bacterial cells characteristic shapes
Composed of peptidoglycan
Two basic types of bacterial cell walls, Gram-positive and Gram-negative

Question 25

Describe peptidoglycan

Answer 25

Composed of a network of repeating sugar molecules and proteins (sometimes other molecules) NAM and NAG are the repeating sugary units N-acetylglucosamine = NAG N-acetylmuramic acid = NAM Tetrapeptides hang off of NAM to create cross-beams

Question 26

Describe gram-positive cell walls

Answer 26

Relatively thick layer of peptidoglycan Contain unique polyalcohols called teichoic acids Appear purple following Gram staining protocol Up to 60% mycolic acid (lipid wall) in acid-fast bacteria helps cells survive desiccation (no peptidoglycan at all, purple shows as a false positive due to mycolic acid)

Question 27

Describe gram-negative cell walls

Answer 27

Have only a thin layer of peptidoglycan Outer membrane beyond the peptidoglycan contains phospholipids, transport proteins (porins), and lipopolysaccharide (LPS or endotoxin) May be impediment to the treatment of disease Appear pink following Gram staining protocol

Question 28

What is diffusion?

Answer 28

The movement of particles from region of high concentration to low concentration. Tends to continue until evenly distributed throughout the medium.

Question 29

What is osmosis?

Answer 29

The diffusion of water across a semi-permeable membrane Movement of water molecules from an area of high concentration of water to an area of low concentration of water – another way of thinking about it is to say water moves from an area of lower particle concentration to an area of higher particle concentration Solutions are named based upon relative solute concentration as compared to cells:

Question 30

What is an isotonic solution?

Answer 30

equal solute concentrations in cell and solution

Question 31

What is a hypotonic solution?

Answer 31

lower concentration of solutes in the solution

Question 32

What is a hypertonic solution?

Answer 32

higher concentration of solutes in the solution

Question 33

What is active transport?

Answer 33

Protein mediated – proteins act as carrier molecules Molecules that are needed inside the cell can be transported against the concentration gradient (from an area of LO concentration to an area of HI concentration)

Question 34

Describe cytoplasm of bacteria

Answer 34

Cytosol – Liquid (80% water) portion of cytoplasm – being the primary site of bacterial metabolic reactions, this solution also contains proteins, metabolic enzymes, lipids, ribosomes, ions, carbohydrates, RNA, electrolytes, the monomers to build organic molecules, etc. Inclusions – May include reserve deposits of chemicals like carbohydrates, phosphates, lipids, air bubbles, etc. Endospores – Unique protective structures only produced by some bacteria that are a defensive strategy against unfavorable conditions Nonmembranous Organelles - Ribosomes - -Sites of protein synthesis - Cytoskeleton - -Plays a role in forming the cell’s basic shape

Question 35

Describe endospores

Answer 35

“Hibernative” state formed by some bacteria during times of environmental stress. Spores are highly resistant to drying & temperature extremes and UV radiation and pH changes . . . (can survive boiling water for hours!) Spores can remain dormant for millennia (1000s of years) before being reactivated

Question 36

What is sporulation?

Answer 36

the process of forming spores

Question 37

What is germination?

Answer 37

spore returning to the vegetative (growing) state

Question 38

Describe the nuclear area aka nucleoid

Answer 38

The DNA of a bacterium is not contained in a nucleus (not surrounded by a separate membrane) The bacterial chromosome is ONE continuous circular loop of double-stranded DNA The chromosome is attached to the inner surface of the cell membrane at a spot called the origin (replication begins here) Occasionally smaller, extrachromosomal loops of DNA called plasmids can be seen separate from the nuclear area

Question 39

Describe ribosomes of bacteria

Answer 39

Composed largely of rRNA and some protein, ribosomes are the ‘protein factories’ of the cell, responsible for translating RNA to polypeptides and proteins. Each bacterial ribosome consists of two subunits 30S 50S Total 70S S= Sedimentary rate (rate of which it settles)

Question 40

Describe archaeal cell walls and cytoplasmic membranes of bacteria

Answer 40

Most archaea have cell walls - Do not have peptidoglycan - Contain variety of specialized polysaccharides and proteins All life, including the archaea, have cytoplasmic membranes for the same basic reasons - Maintain electrical and chemical gradients - Control import and export of substances from the cell

Question 41

Describe eukaryotic cell walls

Answer 41

Fungi, algae, plants, and some protozoa have cell walls Composed of various polysaccharides Plant cell walls composed of cellulose Fungal cell walls composed of cellulose, chitin, and/or glucomannan (yeasts) Algal cell walls composed of a variety of polysaccharides

Question 42

Describe eukaryotic cytoplasmic membranes

Answer 42

As with all life, eukaryotic cells have cytoplasmic membranes, and, like prokaryotic membranes, they are a fluid mosaic of phospholipids and proteins that control movement into and out of cell Contain steroid lipids (cholesterol) to help maintain fluidity (stability) Contain regions of lipids and proteins called membrane rafts

Question 43

Describe eukaryotic ribosomes

Answer 43

Only minor structural differences compared to prokaryotic ribosomes There are still two subunits, but each are larger than prokaryotic a large 60S subunit + a small 40S subunit They combine to form an 80S ribosome

Question 44

Describe the nucleus

Answer 44

Nucleus: contains DNA bound to histones and surrounded by double-membrane (nuclear envelope) with small pores (nuclear pores) The DNA can be found in the form of chromatin or chromosomes Chromatin- in this state 90% of time, uncondensed (opened up and usable) Chromosomes- in this state 10% of the time, condensed (compact and movable) Nucleolus:- condensed regions of DNA where several types of RNA is being synthesized

Question 45

Describe mitochondria of eukaryotes

Answer 45

Major site of energy (ATP) production for the cell. Mitochondria have both an inner and outer membrane (double membrane) Enzymes within the matrix (fluid) and cristae (folds in the inner membrane) are involved in the synthesis of ATP via oxidative phosphorylation (cellular respiration) Mitochondria replicate by binary fission have their own circular DNA & 70S ribosomes

Question 46

Describe chloroplast

Answer 46

Membranous inner sacs called thylakoids contain the chlorophyll and enzymes involved in photosynthesis (making sugars from carbon dioxide and sunlight) Like mitochondria, chloroplasts replicate within the cell by binary fission and have their own circular DNA & 70S ribosomes

Question 47

Explain the endosymbiotic theory (7pt short answer)

Answer 47

Eukaryotes formed from union of small aerobic prokaryotes with larger anaerobic prokaryotes (15x more energy) Smaller prokaryotes became internal parasites Parasites lost ability to exist independently Larger cell became dependent on parasites for aerobic ATP production Aerobic prokaryotes evolved into mitochondria Similar scenario for origin of chloroplasts Proposed by Lynn Margulis in 1966 – rejected by 15 scientific journals Hydrogen hypothesis filled in many blanks to her theory