The Bacterial Cell

Question 1

What are three similarities between eukaryotes and prokaryotes

Answer 1

Both cell types have DNA, a cell membrane, and a cytoplasm that contains ribosomes.

Question 2

Define a prokaryote

Answer 2

A cellular organism in which the cell does not have a true, membrane-enclosed nucleus.

Question 3

List five key differences between eukaryotes and prokaryotes

Answer 3

Prokaryotes are generally 5-10 times smaller than eukaryotic cells Prokaryotic cells do not contain a nucleus Prokaryotic cells contain a single, circular chromosome Prokaryotes contain plasmids (non-chromosomal DNA) which they can transfer between each other. Prokaryotic cells do not contain membrane-bound organelles. Prokaryotic cells contain a complex cell wall(eukaryotic cells generally do not have one - where they do it is simple). Prokaryotic cells reproduce through binary fission, whereas eukaryotes undergo mitosis or meiosis.

Question 4

Define Bacteria

Answer 4

A free living, single-celled prokaryote that reproduces through binary fission.

Question 5

Can all bacteria be grown in vitro?

Answer 5

No. Bacteria are very fussy as to their environment, and only around 20% of bacteria can be grown in a lab, however this technique is very clinically important in identifying and treating bacterial infections.

Question 6

Briefly describe Binary Fission

Answer 6

Binary fission is a five-step process that bacteria use to reproduce: 1. The cell replicates its DNA with prokaryotic DNA polymerase. The process is very similar to eukaryotes, but uses different factors and enzymes that can then be targeted by antibiotics. 2. The cell membrane elongates, separating the two duplicate DNA molecules. 3. A cross wall begins to form between the two DNA molecules, and the cell membrane begins to invaginate. 4. The cross wall forms completely 5. The original cell splits into two daughter cells.

Question 7

Why is 16S rRNA important

Answer 7

16s rRNA is valuable in identifying the particular bacterial species. Some is common to all bacteria, but other parts of the rRNA are unique.

Question 8

Describe the four phases of the bacterial life cycle

Answer 8

1. Lag phase - bacteria are adapting to their conditions and establishing themselves. 2. Log phase - They experience exponential growth, the rate of which depends on the idealness of their environment. 3. Stationary phase - once they have depleted all available nutrients, and only waste and by-products remain. 4. Death phase - where numbers begin to decline.

Question 9

What three factors (2 inputs, 1 output) are crucial in bacterial reproduction?

Answer 9

To reproduce effectively, bacteria require: 1. Energy (from the host or can be synthesised) 2. Nutrients (N, S, C, O) to construct macromolecules and cellular structures (and energy if required) 3. A place for waste products - the relative harmfulness of which is important in classing bacteria as commensal or pathogenic.

Question 10

What are the three categories of bacteria in relation to their use of oxygen?

Answer 10

Aerobic - require oxygen Anaerobic - harmed by oxygen (either strict or obligate anaerobes) Facultative anaerobic - can grow with or without oxygen.

Question 11

Briefly describe the kinds of bacteria that can grow in humans

Answer 11

Psychotrophs can grow in sub-zero temperatures (hence refrigeration), and live in the human body. They include listeria. Mesophiles cannot grow in temperatures below 15 degrees, but hit their peak around 37.

Question 12

Can bacteria survive in the stomach?

Answer 12

Most bacteria cannot, but some may get through and commence growing in the small intestine.

Question 13

Name two bacteria that can survive in acidic environments

Answer 13

Helicobacter and Lactic Acid (lactobacilli acidophilus) bacteria.

Question 14

The bacterial cell wall plays a key role in 4 things - what are they?

Answer 14

1 - Identification (Gram Stain). 2 - Virulence (aherence and gaining entry to eukaryote). 3 - Interaction with host’s immune system. 4 - Key target point for antibiotics.

Question 15

What is Peptidoglycan?

Answer 15

It is a polymer of sugars and amino acids, the thickness of which will define whether a bacteria is Gram-Positive or Gram-Negative. It is composed of a number of chains of alternating acetylmuamic and isomine acids, with the chains held together by peptide linkages.

Question 16

Briefly describe Gram-positive bacteria

Answer 16

Gram Positive bacteria have a very thin periplasmic space sandwiched between the plasma membrane and a thick layer of peptidoglycan. This layer retains the stain of Gram’s iodine even after rinsing (hence Gram-positive). They are unique in having techoic and liptechoic acid protruding from the peptidoglycan, and may or may not have a capsule.

Question 17

Briefly describe Gram-negative bacteria

Answer 17

Gram-negative bacteria have a thin layer of peptidoglycan inside a periplasmic space, which is itself covered by an outer membrane of protein and LPS (lipopolysaccharide). While this is initially stained by Gram’s iodine, it is washed off by the decolouriser.

Question 18

Name Three features of Gram-negative bacteria that make them unique

Answer 18

An outer membrane of LPS. Porin transporters, which take in carbohydrates and lipids, and are important targets for antibiotics. They have endotoxins. These consist of fatty acids linked to a disaccharide polymer (collectively Lipid A), and have polysaccharide chains (O antigen) attached. Endotoxin induces a strong immune response, and is the pathogenic basis of septic shock.

Question 19

What is a serotype?

Answer 19

The classification of strains within a species based on their surface antigens.

Question 20

What are two features used to define serotypes?

Answer 20

The O-Antigen (an antigenic, polysaccharide chain connected to Lipid A). Composition of the O-antigen varies between strains. Capsules - there are many different types of capsules, usually defined by their own adaptive immune response against the host.

Question 21

How would you draw a Gram Positive vs Gram Negative bacteria?

Answer 21