Biology 2.1.1- Cell Structure

Outline the structure and function of the: cytoplasm, nucleus, nucleolus and nuclear envelope

Outline the structure and function of the: cytoplasm, nucleus, nucleolus and nuclear envelope

Cytoplasm: contains all cell organelles

Nucleus: contains chromatin, transcription of DNA

Nucleolus: inside the nucleus, makes RNA and ribosomes

Nuclear envelope: a double membrane, contains the nucleus, has pores to allow substances like RNA to leave the nucleus

Outline the structure and function of the: rough and smooth ER, Golgi apparatus and cell membrane

Rough ER: membrane-bound sacs called cisternae, connected to nuclear envelope, contains ribosomes, folds and processes proteins

Smooth ER: produces and packages lipids

Golgi apparatus: made up of flat membrane-bound sacs, processes, packages and can modify proteins and lipids, makes lysosomes

Cell membrane: made of lipids and proteins, regulates transport of substances

Outline the structure and function of the: ribosomes, lysosomes and mitochondria

Ribosomes: attached to rough ER or independent, not membrane-bound, site of protein synthesis

Lysosomes: round membrane-bound organelles, contain enzymes that break down materials

Mitochondria: releases energy via respiration, producing ATP, consists of the matrix within a membrane folded into cristae, surrounded by an outer membrane

Outline the structure and function of the: vesicles, cilia and centrioles

Vesicles: small fluid-filled sac, transports substances between cells and between organelles

Cilia: hair-like structures on the plasma membrane in some animal cells, contain protein microtubules in a 9+2 formation which let the cilia move, used to move substances in multicellular eukaryotes

Centrioles: hollow cylinders made from protein microtubules, form spindle fibres in mitosis

Outline the structure and function of the: cell wall, vacuole, amyloplasts and chloroplasts

Cell wall: made of cellulose, cell structure and rigidity, pores called plasmodesmata connect cells via cytoplasm for the exchange of substances

Vacuole: membrane called the tonoplast, filled with cell sap, stores substances and maintains cell turgidity

Amyloplast- contains starch grains for energy storage

Chloroplasts: release energy via photosynthesis, contains thylakoid membranes stacked to form grana, and the stroma (like cytoplasm), surrounded by a double membrane

(plant cells only)

Name the organelles found in prokaryotes and outline their functions

What are the differences between prokaryotic and eukaryotic cells?

Process of the excretion of proteins

1. The protein is produced in the ribosomes of the rough ER

2. The protein is pinched off in a vesicle, which carries it to the Golgi apparatus

3. The vesicle fuses with the Golgi apparatus, which processes, packages, and may modify the protein

4. The protein is pinched off in another vesicle which travels to and fuses with the cell membrane

5. The cell membrane opens to secrete the protein

What are the 4 main functions of the cytoskeleton?

1. Support the cell organelles and keep them in place

2. Provide strength and structure to the cell

3. Movement of materials eg. for mitosis

4. Cell movement, as cytoskeleton filaments run through flagella and cilia

Name the three types of cytoskeleton structures, and outline their structure + function

1. Microfilaments: dynamic, contractile fibres made of actin, positioned near cell membrane, cause cell contraction during cytokinesis

2. Microtubules: dynamic, hollow cylinders made of tubulin, can contract and polymerase to change their length, involved in anaphase in mitosis as contracting spindle fibres, help move organelles like vesicles around the cell

3. Intermediate filaments: fixed within the cell, maintain the structure and keep organelles in place

What is the difference between magnification and resolution?

Magnification is how much bigger the image is than the specimen

Resolution is how close together two objects can be before they appear as one under a microscope, ie. how detailed the microscope can see

How do laser scanning confocal microscopes work?

• The specimen is tagged with a fluorescent dye

• Laser beams are fired at the specimen, which gives off light

• This can be detected by a computer to generate an image

How do the two electron microscopes work?

Transmission electron microscope:

• Use electromagnets to focus a beam of electrons at a thin specimen in a vacuum

• The electrons are transmitted but are absorbed by denser parts of the specimen or areas stained using heavy metals

• A computer generates a black and white image, which is darker corresponding to where electrons have been absorbed

Scanning electron microscope:

• Electrons are fired at a specimen in a vacuum and bounce off

• These can be detected at an angle and an image is produced by a computer

What are the pros and cons of light microscopes?

Pros:

• Cheap

• Small size, don’t need installation

• Easy to use and prepare slides for

• Specimens can be living

• Images are coloured, or can be stained

• Doesn’t require a vacuum

Cons:

• Low magnification- max 1500 x

• Low resolution- 0.2 micrometers (because light has a longer wavelength than electrons)

• Can only create 2D images

• Can’t see viruses or full cell structure

What are the pros and cons of SEMs?

Pros:

• High magnification - max 500,000 x (not as high as TEMs)

• High resolution- 0.002 micrometers (as electrons have a shorter wavelength than light)

• Images produced are 3D

• Can see viruses and shows more detail into cell structure and ultra structure

Cons:

• Expensive

• Large, need to be installed

• Hard to use and prepare specimens for

• Requires a vacuum, so samples have to be dead

• Images are black and white (but can be digitally coloured)

What are the pros and cons of TEMs?

Pros:

• High magnification - can be greater than 1,000,000 x

• High resolution- 0.0002 micrometers (as electrons have a shorter wavelength than light)

• Can see viruses and shows more detail into cell structure and ultra structure

Cons:

• Expensive

• Large, need to be installed

• Hard to use and prepare slides for

• Specimens have to be very thinly sliced and can get distorted in preparation

• Images produced are 2D

• Requires a vacuum, so samples have to be dead

• Images are black and white (but can be digitally coloured)

What are the pros and cons of laser scanning confocal microscopes?

Pros:

• Small (but bigger than light microscopes)

• High resolution

• Images produced are 3D

Cons:

• Images are black and white (but colours can be added afterwards)

• Low magnification

How can you use an eyepiece graticule to measure cells?

You first have to calibrate it to find out the actual length of each division on the ruler:

1. Place a stage micrometer slide on the stage

2. Focus the microscope on the lowest power objective lens

3. Move the stage micrometer around to line up the two rulers

4. Count the number of small divisions on the graticule equivalent to 100 micrometers on the stage micrometer

5. Divide 100 by the number counted to find the length that one division represents, and record the result

6. Repeat for the medium and highest power objective lenses

You can then replace the stage micrometer with a slide and measure the length of a cell using the calculated values for the divisions

What is differential staining?

Different stains can be applied to one slide, which are absorbed by different parts of the cell to identify them

What stains can be used in differential staining?

• Acetic orcein stains chromosomes dark red

• Eosin stains cytoplasm dark red/pink

• Iodine stains starch blue-black

• Iodine in potassium iodide solution stains cellulose yellow

• Hematoxylin stains RNA and DNA purple/blue

• Methylene blue is an all-purpose stain, used often to stain DNA blue