2.2 Prokaryotic Cells

Topic 2 Cells

Prokaryotic Cells2.2.1 Draw and label a diagram of the ultrastructure of Escherichia coli (E. coli) as an example of a prokaryote.The diagram should show the cell wall, plasma membrane, cytoplasm, pili, flagella, ribosomes and nucleoid (region containing naked DNA).

2.2.2 Annotate the diagram from 2.2.1 with the functions of each named structure.

2.2.3 Identify structures from 2.2.1 in electron micrographs of E. coli.

2.2.4 State that prokaryotic cells divide by binary fission.

Types of Living Things

Living things are known as organisms.Organisms are made up of one or more cells.Under the five kingdom system, cells can be divided into two basic types:– Prokaryotic cells

• Simple cells without distinct membrane bound organelles– Eukaryotic cells

• More complex with membrane bound organelles

Living Things

Non cellular Viruses

Bacterial cells

Fungal Cells

Protoctistan

Animal Cells

Plant cells

Cellular

Prokaryotic cells

Eukaryotic cells

Types of Living Things

Viruses– Non cellular. Typical size range 20-300nm– Contain no cytoplasm or organelles– No chromosomes, just RNA or DNA– Covered in a protein coat.– Depend on cells for metabolism and reproduction

Bacterial Cells– Single celled. Lack a distinct membrane bound nucleus. DNA usually a

single, naked chromosome– Have cell walls. Many secrete a capsule

Types of Living Things

Protoctistan Cells– Mainly single cells (unicellular) or exist as cell colonies– Possess nucleus and membrane bound organelles– Some are autotrophic and carry out photosynthesis (possess chlorophyll)– Some are heterotrophic

Fungal Cells– Possess a nucleus and membrane bound organelles– Plant like but lack chlorophyll (have a cell wall)– Rigid cell walls that contain chitin– heterotrophic

Types of Living Things

Animal Cells– Exist as part of a multicellular organism– Specialisation of cells into many types (Cell differentiation).– Possess nucleus and membrane bound organelles– Many different types– Heterotrophic

Plant Cells– Exist as part of a multicellular organism– Specialisation of cells into many types (Cell differentiation).– Possess nucleus and membrane bound organelles– Autotrophic: photosynthetic cells with chloroplasts– Cells walls of cellulose

Prokaryotic Cells

Prokaryotic organisms are commonly called Bacteria.They are cells with simple structure.The have no membrane around the nucleus and lack any membrane bound organelles.They have a cell wall.They have a naked loop of DNA which stores the genetic information.They also have circular rings of DNA called plasmids.

Prokaryotic Cells

Functions of Parts of Prokaryotic CellsStructures present in Prokaryotic Cells include:– Cell Wall

• forms a protective outer layer that prevents damage from outside• Prevents the cell from bursting due to high internal pressure

– Plasma Membrane• Controls the transfer of substances in and out of the cell

– Cytoplasm• Contains enzymes that catalyse the chemical reactions of metabolism

– Pili• Are for adhesion allowing bacteria to colonize environmental surfaces or cells and

resist flushing. Some bacteria can produce a special pilus called a conjugation or sex pilus that enables conjugation, the transfer of DNA from a donor bacterium to a recipient to enable genetic recombination.

Functions of Parts of Prokaryotic CellsStructures present in Prokaryotic Cells include:– Flagella

• A slender whip-like structure used for locomotion (‘swimming’).– Ribosomes

• Protein synthesis– Naked DNA (Nucleoid)

• Stores the genetic information that controls the cell and is passed onto daughter cells– Mesosome

• In folding of the plasma membrane• Plays a role in cellular respiration and movement of DNA

Functions of Parts of Prokaryotic Cells

Structures sometimes present in Prokaryotic cells:– Plasmids

• Circular rings of naked DNA• Extra genetic material• Can be passed from one cell to another cell• Used as vectors in genetic engineering

– Slime capsule• Protects the cell against chemicals and drying out

– Photosynthetic Membranes• Possess pigments to assist in photosynthesis

Types of Prokaryote

Prokaryotes are more commonly called Bacteria.Although small and relatively simple in structure, they show a wide range of metabolic activity:– Photosynthesis:

• Blue-green bacteria make their own food by photosynthesis (Autotrophic)).– Nitrogen fixation:

• Nitrogen fixing bacteria in the soil convert atmospheric nitrogen into into nitrogen compounds in the soil as part of the nitrogen cycle.

– Fermentation:• Many bacteria absorb large organic substances, convert them into other

organic substances and release them (Heterotrophic).• e.g.: yoghurt, vinegar and cheese production

Reproduction

Prokaryotes reproduce by binary (‘two’) fission (‘splitting’).The two new ‘daughter’ cells are clones of the original cell – genetically identical.

IBO guide:2.2.1 Draw and label a diagram of the ultrastructure of Escherichia coli (E. coli) as an example of a prokaryote.The diagram should show the cell wall, plasma membrane, cytoplasm, pili, flagella, ribosomes and nucleoid (region containing naked DNA).

2.2.2 Annotate the diagram from 2.2.1 with the functions of each named structure.

2.2.3 Identify structures from 2.2.1 in electron micrographs of E. coli.

2.2.4 State that prokaryotic cells divide by binary fission.