Prokaryotic cell structure - lecture 1

Question 1

what is the cell theory?

Answer 1

• cell is the structural unit of life ; contains genetic and metabolic elements
• cells can only arise by division from a pre-existing cell
• all organisms are composed of one or more cells

Question 2

what does the modern cell theory add to the cell theory?

Answer 2

• energy flow occurs within cells
• heredity information is passed on from cell to cell
• all cells have the same basic composition

Question 3

what are the 2 major types of cells?

Answer 3

1) prokaryotes
- circular DNA free in cytoplasm

2) eukaryote
- linear DNA molecules held in membrane bound nucleus
- contain many subcellular organelles to compartmentalise activities

Question 4

what are the subdivisions of prokaryotes?

Answer 4

1 - bacteria or eubacteria

2 - archaea or archaeons

Question 5

describe the features of the nucleoid

Answer 5

• region of cytoplasm where naked DNA is located
• formed into single loop of supercoiled double stranded DNA
• DNA does not have introns and genes are often grouped into operons

Question 6

describe the features of the plasmid

Answer 6

• small loops of non essential DNA independent of genomic DNA
• can be passed vertically during cell division or horizontally by bacterial conjugation
• natural plasmids may carry antibiotic resistance genes

Question 7

describe the features of storage granules

Answer 7

• serve as store of carbon
• majority of bacteria store either glycogen or poly-beta-hydroxybutyrate - not both
• glycogen granules dispersed through cytoplasm - visible only when stained with specific stain
• stains with fat stain sudan black

Question 8

what are mesosomes

Answer 8

aggregates of tubular membrane structures

apparently derived directly from plasma membrane by invagination

Question 9

what are bacterial microcompartments

Answer 9

-protein shells filled with enzymes for key activities

eg; carboxysomes help autotrophic prokaryotes fix carbon via the calvin cycle

Question 10

what is the function of the plasma membrane

Answer 10

• contains cytoplasm and regulates the movement of materials into the cell
• site of cell wall synthesis
• no mitochondria, therefore enzymes for energy generation need to be organised within plasma membrane

Question 11

what is the function of the outer membrane of prokaryotic cells

Answer 11

• only found in gram negative cells and overlays the cell wall
• protects invading bacteria from host defences - phagocytes, lysosomes
• barrier to entry of antibiotics
• essential nutrients pass through via porins

Question 12

purpose of the bacterial cell wall?

Answer 12

structure:

• resists internal osmotic pressure
• prevents bursting hypotonic media - normal environment for bacteria
• determines the cell shape

Question 13

explain why peptidoglycan is strong

Answer 13

-due to cross-linking of peptide chains

Question 14

function of peptidoglycan?

Answer 14

prevents sugar units of polymer sliding over each other

results in a rigid sac

Question 15

what is the capsule and what is its purpose

Answer 15

• layer of polysaccharide and glycoprotein slime surrounding some bacteria
• may be important in attachment of bacteria to other cells

Question 16

what is the periplasm and what is its purpose

Answer 16

• space between peptidoglycan layer and plasma membrane

- filled with loose peptidoglycan network and enzymes for nutrient acquisition

Question 17

what is the flagellum and what is its purpose

Answer 17

• composed of flagellin

- used to propel the cell

Question 18

what are the key features of a typical prokaryote

Answer 18

• singular circular DNA genome and lack a membrane bound nucleus
• no mitochondria
• no ER or golgi
• storage granules
• a rigid cell wall composed of peptidoglycan
• flagella for motility