Chapter 2 - Basic components

What is a lysosome and why is the membrane that surrounds it so important?

Lysosomes are specialised vesicles that contain hydrolytic enzymes breaking down waste material. The membrane that forms lysosomes has an important role in compartmentalising these enzymes away from cell structures that could be damaged by activity of the enzyme

Explain why cells need to be compartmentalised, and

Incompatible reactions / catabolic and anabolic reactions require different conditions / damage due to hydrolytic enzymes

Describe three examples of compartmentalisation within in an animal cell.

Three named examples - nucleus, vesicle, lysosome, mitochondrion, Golgi body, endoplasmic reticulum, chloroplast

Compare the structure and function of the rough and smooth endoplasmic reticulum

Rough ER has ribosomes attached and smooth ER does not have ribosomes attached rough ER protein synthesis (and modification) smooth ER lipid synthesis

Describe the structure and function of the cytoskeleton

The cytoskeleton has three components: Microfilaments are contractile fibres made of actin that bring about cell contraction during cytokinesis
Microtubules are formed from the cylindrical protein tubulin and form scaffold like structures used both in the movement of organelles and vesicles and as spindle fibres in the segregation of chromosomes/chromatids in cell division; Intermediate fibres give mechanical strength to cells

Describe how the structure of microfilaments and microtubules means these components of the cytoskeleton are involved in the movement of cells but the intermediate fibres are not.

Microfilaments composed of actin (actin is) contractile
Microtubules composed of tubulin, tubulin polymerises contraction and polymerisation lead to change in length of filaments which results in movement of cell
Intermediate fibres have fixed length for stability

What is unique about plant cell walls?

They contain cellulose

Give three functions of plant cell walls.

Prevent cells bursting
Allows turgidity
Idea that keep plants upright

Describe the similarities of differences between a human cell and a plant root cell.

Both have three named organelles (e.g. nucleus, cell surface membrane, mitochondria, ribosomes, Golgi body, endoplasmic reticulum) only plants have two named organelles (chloroplast, vacuole)
Centrioles present in animal cells but not flowering plants

What is the cell theory?

Both plant and animal tissue are both composed of cells
These are basic units of life
Cells only develop from existing cells

Why is staining used in microscopy?

Provides contrast/different structures
Organelles absorb stain differently allowing for identification

Why do microscopes have two lenses?

Objective lens magnifies the specimen
Eyepiece lens magnifies image
Higher magnification

Why should you put all measurements into the same units before carrying out calculations?

Simplifies calculations and reduces errors

Explain how diffraction limits resolution.

Diffraction happens when light passes through structures, light waves spread out, (light waves) overlap, individual objects do not appear separate, causes blurring

What is the difference between contrast and resolution?

Contrast is difference in colour/shade between two objects
Resolution is the ability to differentiate between two structures

Explain why you would see more detail with an electron microscope than with a light microscope

Electron microscopes use electrons instead of light and electrons have a shorter wavelength than light which produces images with a higher resolution

Define the term artefact with reference to microscopy

An artefact is a visible object or distorted cell structure present in an electron micrograph (or other micrograph) due to the sample preparation process

Explain why artefacts are more likely to be produced when preparing samples from electron microscopy than for light microscopy

More sample preparation (in electron microscopy) leads to more damage to specimen, damage results in artefacts

Explain the meaning of the term fluorescence

An emission of light that has been absorbed

State why lasers are used to provide illumination

Increase intensity of light

Explain the pinhole aperture in confocal microscopy

Scattered light / light from outside the focal plane is eliminated, reduces blurring, increases resolution

Why can confocal microscopy not be used for deep tissue imaging?

Idea of light penetration of sample is limited

Dry mount

Specimen prepared for viewing on a microscope slide without the use of water or another liquid.

Wet mount

suspended in water/ immersion oil

Squash slides

lens tissue or 2 slides used to compress sample

Smear slides

Edge of slide is used to smear the sample
Used for viewing blood

What is a gram stain?

Differential stain that distinguishes cells with a gram-positive cell wall from those with a gram-negative cell wall

Gram Stain Preparation

1. Add crystal-violet for 1 min then rinse w/ water
2. Add iodine for 1 min then rinse w/ water
3. Rinse with ethanol for 10 sec. then rinse w/ water
Positive test = gram + bacteria retains stain
4. Add safranin for 1 min then rinse w/ water + bacteria show up red

What is the acid fast technique

Used to differentiate mycobacterium

Acid-fast technique steps

1. Lipid solvent used to carry carbolfuchsin dye into cells
2. Washed with dilute acid alcohol solution, only mycobacterium retains dye

Stages of preparing a slide

1. Fixing - formaldehyde used as preservative
2. Sectioning- samples dehydrated with alcohols and placed in mould with wax to form hard block and then sliced for macrotome
3. Staining
4. Mounting - secured to microscope slide

What does diffraction mean?

Tendency of light waves to spread out Electron microscope has shorter wavelengths preventing light from different structures overlapping

Why is a vacuum used for electron microscopy?

No electrons lost to surroundings
Electron beam travel in straight line

What is metabolism?

Involves both synthesis and breaking down of molecules
Different reactions in different areas of the body

What does DNA do?

Directs all the synthesis of proteins used as enzymes in metabolism

What are microfilaments

Threadlike contractile structures made up of a protein called actin

What are microtubules?

Provide structure for cell and scaffolding for movement.
Make up spindle fibres, flagellum
Made of polymerised tubulin

What are intermediate filaments?

Give mechanical strength and integrity to cells

Protein synthesis

1. Ribosomes bound to endoplasmic reticulum
2. Pass into its cisternae and are packaged into vesicles
3. Vesicles containing synthesized proteins move towards Golgi apparatus via cytoskeleton
4. Vesicles fuse with Golgi apparatus and enter
5. Golgi packages and modifies proteins
6. Secondary vesicles carry proteins that are to be released from the cell
7. Vesicles fuse with cell membrane (surface) releasing contents by exocytosis

Nucleus

Surrounded by a double membrane called the envelope containing pores which enable molecules to enter and leave the nucleus. The nucleus also contains chromatin and a nucleolus which is the site of ribosome production

Rough endoplasmic reticulum

A series of flattened sacs enclosed by a membrane with ribosomes on the surface. RER folds and processes proteins made on the ribosomes.

Smooth endoplasmic reticulum

A system of membrane bound sacs. SER produces and processes lipids.

Golgi apparatus

A series of fluid filled flattened & curved sacs with vesicles surrounding the edges. Golgi apparatus processes and packages proteins and lipids.
It also produces lysosomes

Mitochondria

Usually oval shaped
Bound by a double membrane called the envelope
The inner membrane is folded to form projections called cristae with matrix on the inside containing all the enzymes needed for respiration.

Centrioles

Hollow cylinders containing a ring of microtubules arranged at right angles to each other. Centrioles are involved in cell division.

Ribosomes

Composed of two sub units and are the site of protein production

Lysosome

A vesicle containing digestive enzymes bound by a single membrane.

Role of cytoskeleton

Providing mechanical strength

Aiding transport within cells

Enabling cell movement

Holding organelles in position

Formation of cilia

Site of protein production

Ribosomes

Protein transport

1) Proteins are produced on the ribosomes
2) Proteins which are produced on the surface on RER are folded and processed in the RER
3) The proteins are then transported from the RER to the Golgi apparatus in vesicles
4) They are then modified in the Golgi apparatus
5) Golgi apparatus packages proteins into vesicles to be transported around the cells where they're required. Some of the proteins such as extracellular enzymes leave the cell by exocytosis

Cell wall (prokaryotic cell)

Rigid outer covering made of peptidoglycan

Capsule

Protective slimy layer which helps the cell to retain moisture and adhere to surfaces.

Plasmid

Circular piece of DNA

Flagellum

A tail like structure which rotates to move the cell

Pili

Hair-like structures which attach to other bacterial cells

Ribosomes in prokaryotic cells

Function as sites of protein synthesis. 80s in eukaryotic and 70s in prokaryotic.

Role of membrane in RER

Compartmentalisation
Hold ribosome in place
Separate protein from cytoplasms

What is the mobile phase in chromatography?

The solvent

What is the stationary phase in chromatography?

Chromatography paper

Rf value

distance moved by solute / distance moved by solvent

How is a chromatogram produced?

A spot of the mixture is placed on chromatography paper and left to dry

The chromatography paper is then suspended in a solvent

As the solvent travels up through the chromatography paper, the different components travel at different speeds (larger molecules move slower than smaller molecules)

How do vesicles move around the cell?

They attach to the cytoskeleton

Moved by protein motors

What is the maximum resolution of laser scanning confocal microscope?

200nm

What is the maximum resolution of scanning electron microscope?

3-10 nm

What is the maximum resolution of transmission electron microscope?

0\.5 nm

What is the image appearance of laser scanning confocal microscope?

2D/3D

coloured

What is the image appearance of scanning electron microscope?

3D

black and white

What is the image appearance of transmission electron microscope?

2D

black and white