Prokaryotes form & function

Question 1

What size range are prokaryotes? What size is E.coli?

Answer 1

Size range: 0.2 -750 um

Typically: 0.5-5 um

E. coli 1-2 um

Question 2

Why are prokaryotes so small?

Answer 2

Fick’s law of diffusion

Larger cells reach a point where they can’t diffuse nutrients through the cell quick enough to compete with smaller cells

Smaller cells can also grow faster, out competing larger cells.

The lower limit in size is set by the size of DNA and proteins required to be viable

Question 3

What is the function of the cell/cytoplasmic membrane?

Answer 3

Permeability barrier – stops solutes moving in and out of cell and separates cell from its environment.

Protein anchor - participate in transport, bioenergetics and chemotaxis

Energy conservation - allows generation of energy by maintaining proton gradient so protons/hydrogen ions are positively charged, allowing cell to maintain a gradient between inside of the cell and the environment.

Question 4

What is the structure of a cell membrane?

Answer 4

Lipid bilayer - hydrophobic and hydrophilic

Transport proteins act as pores and channels for solute allowing the controlled movement of solute across the membrane (selectivity)

Proteins stabilise the structure of the fluid lipids

Question 5

Features of lipid bilayer

Answer 5

A great permeability barrier

Fluid and flexible (but not very strong).

Question 6

What is a monolayer?

Answer 6

Two tails with a head at each end.

Some archaea have this instead of bilayer

Question 7

What is the cell wall in Gram +ve bacteria made up of?

Answer 7

Simple wall

Multiple sheets of peptidoglycan (protein and sugar polymer).

Up to 90% of wall is peptidoglycan.

Is permeable to small molecules.

Question 8

Features of cell wall in Gram -ve bacteria and what is it made up of?

Answer 8

Inner membrane

Periplasmic space containing peptidoglycan and proteins/enzymes

Only around 10% peptidoglycan

Second layer of lipids and sugars, the ‘Lipopolysaccharide layer’

Outer layer is more permeable to smaller molecules (not proteins) due to porins.

Question 9

What is Gram stain?

Answer 9

1884

Uses crystal violet that is trapped in the walls and stains the violet when under a microscope.

Gram negative bacteria stain pink as they have two membranes.

Question 10

What are archaea cell walls made up of?

Answer 10

Pseudomurein (a polysaccharide), or S-layers: interlocking protein and glycoprotein molecules.

(S-layers are also found in some bacteria, but don’t make up the bulk of the cell wall).

Question 11

What are capsules?

Answer 11

Surround cell

Made up of Polysaccharide (sugar polymer)

Gives cell protection and may help evade immune systems

Also allows some cells to ‘stick together’ forming biofilms

Question 12

What are Fimbriae & Pili?

Answer 12

Fimbriae - Protein filaments, allows attachment to tissues (pathogenic bacteria)

Pili - longer, 1 or a few per cell, Help the cell attach to tissue (in pathogenic bacteria)

Can be used to transfer genetic material in a process called conjugation

Question 13

What are flagella?

Answer 13

Protein filaments that rotate and propel cell through water.

Prokaryotic flagella can be ATP-driven (Archaea) or proton-driven (Bacteria).

Question 14

What are the main characteristics of a prokaryotic cell?

Answer 14

Cell wall

Cytoplasmic membrane

Nucleoid

Cytoplasm

Plasmic

Ribosomes

Question 15

What is a nucleoid?

Answer 15

Contains main genetic information - double stranded DNA

Question 16

What is a Plasmid?

Answer 16

Circular loop of double stranded DNA - contains genes

Question 17

What are ribosomes?

Answer 17

Translate mRNA to proteins in the cytoplasm

Question 18

What is binary fission?

Answer 18

DNA copied

Cell divides

Each daughter cell has copy of original double stranded DNA and half the cytoplasm, cell membrane and cell wall.

Relies on enzymes helicase and primase, RNA primer so DNA polymerase can add nucleotides to one of the strands of DNA to make double stranded DNA.

Question 19

What is horizontal gene transfer?

Answer 19

Transfer of genetic information between cells

Question 20

What is transformation?

Answer 20

Process of horizontal gene transfer by which somebacteriatake up foreign genetic material (naked DNA) from the environment.

When experiencing a new environment they can add genes to their genome that would benefit them

Question 21

What is conjugation?

Answer 21

Plasmid is passed and copied from
one prokaryotic cell to another, through pili

A single stranded piece of plasmid
DNA is passed to the recipient.

The recipient cell synthesises a new
DNA strand (complimentary DNA strand).

Both cells end up with a double stranded copy of the plasmid DNA (genes).

Question 22

What is transduction?

Answer 22

Accidental

When Bacteriophages (dominant virus) replicate their DNA they can sometimes pick up DNA from their host cells.

Very rarely this can result in a stable transformation transduction event where DNA is incorporated into host.

Question 23

Core genome vs pan genome

Answer 23

core genome: shared by all strains of the species

pan genome: includes core plus genes present in some but not all strains of the species

Question 24

What are cell inclusions?

Answer 24

Inclusions function as
energy stores of stores
of functional building
blocks.

Question 25

What storage vesicles do prokaryotic cells have?

Answer 25

Carbon stores – poly-hydrocarbons, glycogen

Polyphosphate – required for DNA and lipid synthesis

Sulphur – Oxidised as energy source in some forms of metabolism

Question 26

What are magnetosomes?

Answer 26

Exact purpose not know but could allow bacteria to orientate themselves to earths magnetic field

Question 27

What are gas vesicles and their purpose?

Answer 27

Found in bacteria and archaea

Made of proteins impermeable to water and solutes but permeable to gases.

Make cell less dense and therefore allow changes in buoyancy.

Question 28

What are endospores?

Answer 28

Some prokaryotes can form endospores.

Extremely resistant to heat, harsh chemicals and radiation.

Normally occurs when nutrients become limiting.

Can survive for many years before ‘germinating’.