A2.2: Cell Structure

Magnification formula

Measured size of image/Actual size of specimen

How many micrometers to a mm?

1,000

Light microscope max. magnification

2,000x

Electron microscope max. magnification

+500,000x

Prokaryote size range

1-10μm

Eukaryote size range

10-100μm

Freeze fracture

Making a biological sample by freezing the specimen and physically breaking it, which makes a plane that is visible with a microscope.

Common in all cells

• DNA in some form

• Cytoplasm made mainly of water

• Plasma membrane

• Conduct all functions of life

Differences between prokaryotes and eukaryotes

• Enclosed or nucleoid DNA

• Organelles present

• Mitochondria present

• Cell size

• Ribosome size

Capsule

Additional external layer present in some bacteria, made of a polysaccharide. Allows certain bacteria to adhere to teeth and skin.

Plasmids

Seperate DNA units that may occur in bacteria. They reproduce independently of chromosomal DNA.

Binary fission

Bacterial cell division

Centrioles

Help facilitate nuclear division: comprised of microtubules, which pull chromosomes apart during mitosis.

Lysosomes

Sacs which can contain and transport up to 40 enzymes, fuse with old or damaged organelles to break them down.

Functions of life:

Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, Nutrition, Metabolism, Homeostasis

Unicellular execution of life forms

• Flagellum facilitate movement

• Vacuoles isolate and store waste, also carry out digestion

• Cell membrane controls movement in and out of cell

• Mitochondria produce energy

• Ribosomes allow growth and repair

Examples of atypical eukaryotes

• Coenocytic hyphae

• Phloem sieve tube

• Skeletal muscle

• Red blood cells

• Nerve cells

• Sperm cells

ER functions

• Transports materials internally through the cell

• Has specialised enzymes as embedded proteins in its surface, functions include

  • Production of membrane and cellular lipids

  • Production of sex hormones

  • Detoxification of drugs (liver)

  • Storage of calcium ions (muscle cells)

  • Helping release glucose from liver into bloodstream when neccessary

Rough ER functions

Protein synthesis and transportation

Prokaryote ribosomes

70S

Eukaryote ribosomes

80S

Golgi Apparatus

Collects, packages and modifies materials from the cis side (facing the ER) through the cisternae and over to the trans side, where the modified materials exit into the cytoplasm.

Mitochondria structure

Double membrane, own DNA, cristae form layers in inner membrane providing a larger surface area for chemical reactions. Produces and contains own ribosomes. This contributes to the endosymbiotic theory.

Human cell with no nucleus

Red blood cell

Chloroplast structure

Double membrane, own DNA, own ribosomes. Inner layer forms grana, made of piles of thykaloids.

Coenocytic hyphae

Fungi filaments lacking cross-walls, results in one large cell with multiple nuclei

Ploem sieve tube elements

Plant cells with minimal cell components, pores in end wall to allow transport of water through plants.

Red blood cells specialisation

Large surface area, no nucleus, allows them to carry large amounts of oxygen

Sperm cells specialisation

Lots of mitochondria and a tail