Foundations in Biology - Cell structure

Light/optical microscopes

• Poor resolution due to long wavelength of light

• Living samples can be examined and a coloured image is obtained

• Cheap and portable

Transmission electron microscopes

• High magnification and resolution

• Short Wavelength of beam of electrons

• Uses electromagnet - can’t use living samples air would absorb electrons

• Must be very thin - in vacuum - good for internal structure

• Electrons pass through specimen to make image

• Black and White

Scanning electron microscopes

• High magnification and resolution

• Short Wavelength of beam of electrons

• Uses electromagnet - can’t use living samples air would absorb electrons

• Doesn’t need to be thin

• Electrons bounce of specimen to make a 3d image

Laser scanning confocal microscope

• Higher resolution and 3D imaging

• Laser light is used to create an image

Resolution - minimum distance between two object where you can view them as separate

Magnification - how much larger image is compared to object

Slide preparation

Dry mount - thin slices or whole specimen is viewed placed with just a coverslip e.g. a thin slice of plant tissue, hair

Wet mount - Specimen is added to water or stain before coverslip is added with a needle to prevent air bubbles e.g. living aquatic organisms

Squash slide - Push down on coverslip for very thin layer of cells e.g. root tip

Smear slide - use edge of another slide to smear sample across the slide - smooth thin even coating e.g. blood cells

Calibrating

• Line up stage micrometer and eyepiece graticule

• Count how many division on epg fit into one micrometer

• 10um micrometer 10/ number of divisions of epg

Magnification = size of image/ size of real object

Differential staining - Stains bind to different structures and stain them differently

• Methylene blue is an all-purpose stain.

• acetic orcein binds to DNA and stains chromosomes dark red

• Eosin stains cytoplasm; Sudan red stains lipids

• Iodine in potassium iodide solution stains the cellulose in plant

• cell walls yellow,

  Eukaryotes

  Nucleus

• nuclear envelope - double membrane - nuclear pores (mRNA to leave)

• Protein bound chromosomes

• Nucleolus - where RNA and ribosomes are made

• DNA replication + transcription - contains genetic code

Flagella

• Whip like structure for mobility

Cilia

• Sweep substances with hair like projections

Centrioles

• Made of microtubules

• Form centrosome

• Form spindle fibres

Cytoskeleton

• Network of fibres in cytoplasm

• Provides mechanical strength - maintain shape

• Holds organelles in fixed shape

RER

• Folded membranes

• Ribosomes attached - site of protein synthesis

• Folding of proteins

SER

• Synthesis of lipids and carbohydrates

• Also stored

Golgi apparatus

• Folded membrane - more curved

• Vesicles are released - new cell

• proteins further modified

• Glycoproteins formed

• Lysosomes created

Lysosomes

• Contain lysozymes digest pathogens

• Fuse with phagocytes

Mitochondria

• Site of aerobic respiration

• Contain ribosomes and DNA ro create enzymes

• ATP production

Production and Secretion of proteins

1. mRNA leaves the nucleus through a nuclear pore.

2. mRNA attaches to a ribosome, in this case attached to RER

3. Ribosome reads the instructions to assemble

   the protein (insulin).

4. Protein molecules are ‘pinched off’ in vesicles and

   travel towards Golgi apparatus

5. Vesicle fuses with Golgi apparatus.

6. Golgi apparatus processes and packages protein molecule - ready for release.

7. Packaged protein molecules are ‘pinched off’ in vesicles from Golgi apparatus

   and move towards plasma membrane.

8. Vesicle fuses with plasma membrane.

9. Plasma membrane opens to release protein molecules outside to cells

Differences between prokaryotic cells and eukaryotic cells

• Prokaryotes are much smaller - no membrane bound organelles

• DNA is not in a nucleus and has single circular DNA

• Cell wall made of murein

• Can contain capsule, flagellum, plasmids

• Ribosomes are much smaller 70s eukaryotes have 80s