3- Structure of prokaryotic cells and of viruses

What are prokaryotic cells?

• Cells with no distinct nucleus

• And no membrane-bound organelles

Which four organelles are found in all prokaryotic cells?

• Cytoplasm

• Cell surface membrane

• 70S ribosomes

• Cell wall

What is the difference between 70S ribosomes and 80S ribosomes?

70S ribosomes are smaller

What are the three functions of a prokaryotic cell wall?

• Protection against mechanical damage

• Maintaining the cell shape

• Prevent the cell from bursting (osmotic lysis)

What is the structure of a prokaryotic cell wall?

• Made up of murein or peptidoglycan

• 10-80 nm thick

What are three organelles that are sometimes present in prokaryotic cells?

• Plasmids

• Flagellum

• Capsule

What is the structure of the flagellum?

• Tail-shaped

• There may be more than one in each prokaryotic cell

What is the function of the flagellum in prokaryotic cells?

• To help the prokaryotic cell move towards food and away from danger

• This is known as locomotion

What is the structure of the capsule?

• A layer outside of the prokaryotic cell wall

• Made up of sugars and polysaccharides

What is the function of the capsule in prokaryotic cells?

• Protection against other cells

• Adherence to other bacterial cells for further protection

What are plasmids?

• Small circular pieces of DNA

• Possess genes that may aid the survival of bacteria in adverse conditions (e.g. to produce enzymes that break down antibiotics)

What is the size of a typical bacterial cell?

0.1 to 10 micrometres long

What do bacterial cells use as food reserves?

• Glycogen granules

• Oil droplets

What is the genetic material in prokaryotic cells in the form of?

• A circular strand of DNA

• Plasmids

What word can viruses be described as that means they are not made up of cells?

Acellular

Why are viruses described as non-living?

They do not have their own metabolism and cannot replicate on their own

Compare the size of viruses to the size of cells.

Viruses are much smaller than cells

What three structures do all viruses contain?

• Genetic material

• Protein capsid

• Attachment proteins

What form can the genetic material take in viruses?

• RNA or DNA

• Double-stranded or single-stranded

What is the function of the protein capsid in viruses?

It stores and protects the genetic material

What are attachment proteins and what is their function?

• Proteins found on the surface of viruses

• Used to attach to host cells

What structure do some viruses contain?

A lipid envelope

What is the lipid envelope made up of?

Phospholipids stolen from host cell membranes

What is the lipid envelope?

An outer phospholipid layer found in viruses