Bacterial Cell - Structure & Function Flashcards
Name one positive and one negative effect that microorganisms can have on food.
Positive: microbial transformations, e.g. live yoghurt, yeast, blue cheese.
Negative: food spoliage.
What are the positive and negative effects of microorganisms on agriiculture?
Positives: nitrogen-fixing bacteria, cellulose degrades bacteria in the rumen of cattle, bacteria regerate nutrients in soil and water.
Negative: diseases in plants and animals.
What is the cell wall of bacteria made of and what is its function?
The bacterial cell wall is made of peptidoglycan, a glycan (sugar) backbone with cross-linked peptide side chains. It gives the cell rigidity and shape and protects against osmotic pressure.
When gram stained, gram positive bacteria show purple and gram negative bacteria show pink. What is the cause of this difference?
Gram positive bacterial cells have a thick layer of peptidoglycan in their cell walls, whereas gram negative cells have a thinner layer of peptidoglycan, a periplasmic space and an outer membrane. The outer membrane of gram negative bacteria resembles the phospholipid bilayer of the plasma membrane.
What are endotoxins? Why do they cause septic shock?
Endotoxins are formed from lipopolysaccharides found in the outer layer of gram-negative bacteria, which are released as endotoxins when the cells die.
Endotoxins cause septic shock when they enter the bloodstream follwing infection with gram-negative bacteria.
Name the bacterial cell structure from this description:
It is a phospholipid bilayer, 7.5nm wide with protein permeases. Some of these proteins allow small molecules into the cell, whilst others take part in signal transduction and others have roles in the electron transfer chain and cell wall synthesis. Turgor pressure helps to maintain the shape of the cell.
Cytoplasmic membrane.
The membrane also allows for the generation of a proton motive force (a form of transport). Gases can diffuse across the membrane and water tends to move across by osmosis.
What is the function of the glycocalyx?
It is a capsule or slime layer of sugar polymers which protect th cell against attack, dehydration, and promote adhesion to inert surfaces.
Which industrial food thickener is made from the glycocalyx of a bacterium?
Xanthan gum.
Some bacterial cells have ……….. on their surfaces, hair-like structures which help them to rotate and swim.
Flagella.
Name the small, hair-like structures found on the surface of bacteria which allow them to attach onto surfaces.
Pili (fimbriae).
Found on the surface of bacterial cells, what are endospores and why can they be dangerous?
Endospores are formed in vegetative bacterial cells, they can lie dormant through extreme conditions and produce a new vegetative cell when conditions are more favourable.
Endospores can cause severe illness, they are heat resistant and germinate in cooled food. One example is Clostridium botulinum.
What % of the cytoplasm of bacterial cells is water?
80%.
True or false: bacterial cells have membrane-bound compartments, organelles and a nucleue, the same as in eukaryotic cells.
False. The organelles in bacterial cells are ‘floating’ in the cytoplasm. All of the components of the cell contribute to its internal osmolarity.
What is the fastest way to identify a microbe? Why?
By amplifying the 16s ribosomal rRNA found in the 50s subunit. This rRNA encodes the genes for mRNA and therefore protein synthesis, which is unique to each microbe.
Is the site of antibiotic action the 30s subunit or the 50s subunit of the prokaryotic ribosome?
Antibiotics act on the 50s subunit of the prokaryotic ribosome, which is the site of protein synthesis.
