Lecture 2a: Cell Structure and Function

magnification

ability to make an object larger

resolution

the ability to distinguish small objects that are close together as separate and distinct

Simple staining

One dye used to color specimen

Simple stain - basic dye

Positively charged chromophore, which binds to negatively charged cellular components

simple stain - acidic dye

- charged chromophore, binds to + charged cellular components.

The gram stain

separates bacteria into 2 groups based on cell wall structure

Gram positive cells are ____ because they….

purple , retain the primary stain

Gram negative cells are ___ because they…

pink/red, lose the primary stain and take color of counterstain

acid fast stain, how does it work and what is the result?

Detect mycolic acid in the cell of of the genus Mycobacterium

Mycobacterium retain the primary stain (pink), and everything else takes on counterstain (blue)

Endospore stain, how does it work and what is the result?

Endospores retain primary color (green) and cells are counterstained (pink)

phase-contrast microscopy: How, Image, Key points

1. Phase ring amplifies difference in refractive index of cell and surroundings

2. Dark cells on a light background

3. No stain needed, can see live samples

Bright-field microscopy: How, Image, Key Points

1. Contrast between specimen and surroundings

2. normal magnified image

3. basic scope

Dark field microscopy: how, image, key points

1. Hollow cone of light, only refracted light enters objective

2. bright specimen on light background

3. good for bacteria that doesn’t stain well

Fluorescence microscopy: how, image, key points

1. specimen emits one colour when lit by another

2. glowing specimen

3. cells can have natural fluorescence or we use fluorescent dye

Differential interface contrast (DIC) microscopy

• uses a polarizer to create 2 beams of light

• gives structures a 3D appearance

confocal scanning laser (CSL) microscopy

• uses a computerized scope and laser

• focuses on single layers, then compiles layers into 3D image

electron microscopy

• uses electrons instead of light photons

• electron wavelength shorter than light therefore higher resolution

Transmission electron microscope (TEM): how, image, key points

• electrons pass through specimen

• can see internal structures

• specimen must be very thin and stained with metals

Scanning electron microscopy (SEM): how, image, key points

• electrons scan specimen

• 3D image of specimen surface

• specimen is coated with a thin film of heavy metal

how can selective forces shape cell morphology?

• small cells/high SA:V - nutrient uptake

• helical/spiral shape - swimming motility

• filamentous - gliding motility

Advantages to being a smaller cell

small cells have more surface area relative to cell volume

1. support greater nutrient uptake exchange per unit cell volume

2. grow faster than larger cells

plasma membrane: what is it and function

• thin structure that surrounds the cells

• highly selective permeable barrier. concentrates nutrients and excretes waste

how is the cytoplasmic membrane stabilized ?

1. Mg and Ca by forming ionic bonds w negative charges on the phospholipids

2. hydrogen bonds and hydrophobic interactions

what kind of linkages do archaeal membranes have? bacterial?

archaeal has ether, bacterial has ester

what makes archeal membranes so heat resistant?

lipid monolayer

list 3 membrane functions

1. permeability barrier

2. protein anchor

3. energy conservation

how do archaeal membranes differ from bacterial membranes?

1. lack fatty acids, have isoprenes instead

2. instead of phospholipids, have glycerol diethers/ tetraether

3. can exist as monolayer, bilayer or a mix of both