Structure And Function In Bacteria 2

Question 0

What is the ratio of phospholipids to proteins in the cell membrane?

Answer 0

40% phospholipid 60% protein

Question 1

What are the general features of a plasma membrane? (13)

Answer 1

Cytoplasmic membrane
Most dynamic structure of prokaryotic cell
Encompasses cytoplasm of all cells
Selectively permeable barrier
Allows water passage and uncharged molecules
Osmotic or permeability barrier
Location of transport systems for specific solutes
Energy generating functions
Synthesis of membrane lipids
Synthesis of PGL
assembly and secretion of extra cytoplasmic proteins
Coordination of DNA replication and segregation, septum formation and cell division
Location of specialise enzyme systems

Question 2

What do bacterial membranes lack and what do they have to compensate?

Answer 2

Sterols

Steroid like hopanoids

Question 3

What are most membrane associated lipids and which ends interact with water and without?

Answer 3

Amphipathic- having both hydrophobic and hydrophilic ends
Polar - hydrophilic - interacts with water
Non-polar- hydrophobic - insoluble in water, interact with one another

Question 4

What are the two types of plasma membrane proteins?

Answer 4

Integral/transmembrane

Peripheral

Question 5

What are the features of integral/transmembrane proteins?

Answer 5

Not easily extracted from membranes
Insoluble in aqueous solution when freed of lipids
Amphipathic -hydrophobic regions in buried in lipid hydrophilic project from membrane surface
Carbohydrates are attached to outer surface of membrane proteins
Responsible for secretion, energy conserving and interaction with the environment

Question 6

What are the features of peripheral proteins?

Answer 6

Loosely connected to membrane
Easily removed
Soluble in aqueous solution
20/30% of total membrane protein

Question 7

What are mesosomes?

Answer 7

An organelle of bacteria that appears I electron micrographs as an invagination of the plasma membrane and is a site of localisation of respiratory enzymes

Question 8

Features of the nucleoid?

Answer 8

Single, circular loop of essential double stranded DNA aggregated in a dense area of the cell known as the nucleoid
Contains cells and chromosomes + numerous proteins
Some organisms have a linear chromosome while others may have more than 1
Chromosomes are much larger than the length of the cell

Question 9

How many genes are in a bacterial cell and how are they packaged?

Answer 9

3-4000

Packaged by supercoiling

Question 10

Features of plasmids?

Answer 10

Small, circular, 1/10th the size of chromosome
Double stranded DNA
Free in cytoplasm
Can link into chromosome
Not essential for metabolic growth or cell reproduction
Replicate independently
Can be removed by curing

Question 11

What are some of the functions of plasmids?

Answer 11

R plasmids - resistance to antibiotics
Fertility factors
Virulence plasmids 
Metabolic plasmids 
Bacteriocins - destructive chemicals

Question 12

Features of Fimbriae?

Answer 12

Prokaryotes have short, fine, hairlike appendages that are thinner than flagella
Slender tubes composed of helically arranged protein subunits and are about 3-10nm in diameter and up to several micrometers long
A cell may be covered with up to 1000 Fimbriae
Attach bacteria to solid surfaces
May be used in locomotion

Question 13

Features of pilli?

Answer 13

Often larger than Fimbriae 9-10nm in diameter
Bacteria have about 1-10 sex pili per cell
Genetically determined by conjugation plasmids and are required for conjugation

Question 14

What is the role of the flagellum and what are the three components of it?

Answer 14

Movement of cell

Filament, hook and basal body

Question 15

Features of flagella?

Answer 15

Bacterial flagella are slende, rigid structures about 20nm diameter and up to 15-20 micrometers long
Threadlike loco motor appendages extending outward from the plasma membrane and cell wall
Involved in motility, movement over surfaces and attachment
Bacterial species often differ distinctively in their patterns of flagella distribution and so are useful in identification

Question 16

Name 4 types of flagella?

Answer 16

Monotrichous - 1 flagellum
Lophotrichous - multiple at 1 side
Amphitrichous - multiple at 2 sides
Peritrichous - multiple covering whole cell

Question 17

What is a periplasmic flagella?

Answer 17

A type of modified flagella
Found in a group of bacteria known as spirochates
Consists of a filament and a hook but the entire structure is located between the cell wall and the membrane (the periplasmic space)
The filament is wrapped around the cell and is free to contract and relax causing a twisting, flexing movement of the entire cell

Question 18

What are the three parts of the flagella and what are there functions?

Answer 18

Filament - rotates, composed of protein flagellin
Hook - connects basal body and filament
Basal body - complex, not fully understood. Consists of a series of rings associated with layers of the bacterial cell

Question 19

What is the basal body made up of?

Answer 19

A rod, 4 rings (C ring acts as flagellum motor) and a motor

Question 20

What is the motor in the basal body of a flagellum composed of?

Answer 20

Rotor - M, S and C ring

Stator - MotA and MotB

Question 21

How does the flagellum move?

Answer 21

Proton motive force - differences in charge and pH across membrane
Created by transfer of electrons down the electron transfer chain transfer releases energy

Question 22

What is chemotaxis?

Answer 22

Movement in the cell in response to chemical signals either positive or negative

Question 23

How is chemotaxis accomplished ie. In what ways do bacterium move?

Answer 23

Runs - movement in a linear direction created by anti clockwise flagellar rotation (sends cell moving forward)
Tumbles - when cell stops and reverses direction created by a clockwise flagellar rotation (sends cell tumbling randomly)

Question 24

Features of ribosomes?

Answer 24

Site of protein synthesis within the cell
Composed of rRNA and proteins
Cytoplasmic proteins
Plasma membrane - cell envelope/transported to outside

Question 25

What are gas vacuoles used for?

Answer 25

Buoyancy for aquatic bacteria (halobacterium)

Question 26

What are magnetosomes?

Answer 26

Orient themselves to earths magnetic field
Magnetic
Enclosed within plasma membrane