Bio Miss M: Cells and microscopy

The 2 main types of organisms are

• Eukaryotic = made from eukaryotic cells which contain a nucleus and membrane bound organelles

• Prokaryotic = made from prokaryotic cells, they are single-celled organisms which lack a nucleus and membrane bound organelles

Define organelles

Structures within cells that have a specific function

Define ultrastructure

Detail which can only be seen using an electron microscope

Animal cells

Cell surface/plasma membrane

Consists of lipids and proteins involved in the transport of substances into and out of cells

Nucleus

Controls the cells activities and contains genetic material for making proteins

Nuclear envelope

A double membrane which surrounds the nucleus

Nuclear pores

Gaps in the nuclear membrane which allow substances to enter and leave the nucleus (mRNA)

Nucleolus

Contains RNA used to make ribosomes

Chromatin

Made up of DNA wrapped around histone protiens and coils to form chromasomes

RER and SER

• Series of membranes with fluid filled cavities called cisternae which form channels to transport substances around the cell

• RER is coated in ribosomes

• SER contains enzymes responsible for synthesising and processing lipids

Ribosomes

• Site of proteinsysnthesis

• Free floating ribosomes make proteins used inside the cell

• Ribosomes on RER make proteins that are secreted outside the cell

Golgi apparatus

Made from membrane bound flattened sacs and modifies proteins

Vesicle

Brings proteins to and from the golgi apparatus

Lysosomes

• Vesicles made by gogi apparatus and contain hydrolytic enzymes

• They engluf and digest old organelles and foreign matter which is reused by the cell

Mitochondria

• Site of aerobic respiration used to make ATP

• Inner membrane is folded into cristae

• The matrix contains enzymes for respiration

Plant cells

Chloroplasts

• Have an OM and IM

• Within the chloroplast there are thylakoids

• Stack of thylakoids = granum (pl. grana) and they are the sites of photosynthesis

Cellulose cell wall

Provides strength and support to plant cells

The cytoskeleton

Made of 3 components:

• Microfilaments- made from actin and responsible for cell movement and contraction

• Intermediate filaments- provide mechanical strength

• Microtubules- made from tubulin proteins and act as tracks for movement of organelles/vesicles through the cell using motor proteins

Cilia

Small hair like structures made from centrioles formed by microtubules

Protein production (eg. for insulin)

• Insulin gene is transcribed into mRNA in nucleus

• mRNA leaves nucleus through nuclear pore

• mRNA attaches to ribosome on RER + insulin protein is assembled

• Insulin is folded and processed in RER

• Insulin molecule is pinched off in a vesicle which moves towards the Golgi apparatus

• Insulin vesicle fuses with Golgi releasing insulin into it

• Insulin moves through Golgi and is further processed

• Insulin molecule is pinched off in a vesicle and moves towards plasma membrane

• Vesicle fuses with membrane, membrane opens up releasing insulin out of cell (exocytosis)

Prokaryotes

Pilli

Projections that allow bacteria to adhere to host cells or each other

Plasmids

Small rings of DNA which gives a cell extra properties

Eukaryotic vs prokaryotic cells

Define magnification

How many times bigger an image appears compared to the real object

Define resolution

The minimum distance at which two points can be distinguished from each other

Light microscopes

• They use visible light and 2 lenses to magnify an object

• Specimen can be living or dead

Magnification of eyepiece lens

Always 10x

Total magnification equals

total magnification = eyepiece magnification x objective magnification

Electron microscopes

• Use a beam of electrons to magnify an image

• The specimens are dead

2 types of electron microscopes

• Scanning electron microscopes (SEMs)

• Transmission electron microscopes (TEMs)

How does TEM work?

• Pass a beam of electrons through a think chemically fixed spcimen + electrons are absorbed by specimen

• Produces a high resolution black and white 2D image of a specimen (electron micrograph)

How does SEM work?

• A beam of electrons is passed across a specimen causing electrons on specimen to bounce off and be focused on a screen

• Produces a 3D image of the surface of the object

Magnification equation

Magnification = image size / actual size

Mounting

Specimens can be wet or dry mounted

How to dry mount

A thin slice of stained specimen is placed directly onto a slide using forceps then a cover slip is placed ontop

How to wet mount

A small drop of water/immersion oil is paced on slide then stained specimen is placed ontop then cover slip is planed ontop starting at a right angle to avoid air bubbles

How do stains work?

• Stains are coloured chemicals which bind to molecules on the surface of a specimen to make it visible

• Staining increases contrast

What is differential staining?

When different chemicals bind to different structures, more than one stain can be used at once

3 stains and what they stain

Eosin stains cytoplasm red

Methylene blue stains DNA blue

Iodine stains plant cell walls

Rules for drawing images from microscopes

• Include title + state magnification

• Use white unlined paper

• No shading use smooth continuous lines

• Label lines should not cross or have arrowheads

• Label lines should be parallel to top of page

Eyepiece graticule

• A transparent rules fitted onto eyepiece lens of a light microscope

• As magnification is increased length of eyepiece graticule remians constant so eyepiece has to be calibrated at different magnifications to determine actual width of divisions

Stage micrometer

• Used to calibrate the eyepiece graticule

• It is a microscope slide with a ruler which is 1000µm long and divided into 100 divisions (each division = 10µm)

Graticule division equation

eyepiece division length = visible stage micrometer length / no of equivalent eyepiece divisions that fit

How to calibrate an eyepiece graticule

• Set up microscope on desired magnifiction

• Fit eyepiece graticule to microscope

• Place stage micrometer on stage

• Line up 2 scales by moving the micrometre to align the two 0s

• Choose set no. of divisions on graticule and count equivalent no. of divisions on micrometer

• Use eyepiece division length equation