Topic 2.1 Eukaryotic and Prokaryotic cell structure and function

Question 1

State the principle of cell theory

Answer 1

Cells are the fundemental units in all living organisms. They determine the function and organisiation of all biological systems. Cell theory is accepted as a unifying concept in biology.

Question 2

State the relationship between a system and specialised cells

Answer 2

Specialised cells -> tissues that perform a specific function -> organs made of several tissue types -> organ systems

Question 3

Who are the three “architects” of cell theory, what were the concepts they proposed?

Answer 3

• Mathius Schleiden (1804-1881) - the botanist - proposed plants are made from cells
• Theodore Schwann (1810-1882) - the physiologist - proposed animals are made of cells
• Rudolf Virchow (1821-1902) - the doctor - proposed cells come from pre-existing cells

Question 4

What is a prokaryote?

Answer 4

Unicellular organisms with no membrane bound organelles - e.g. bacteria

Question 5

What is the nucleoid?

Answer 5

Irregularly-shaped region of cytoplasm where loop of bacterial DNA is located

Question 6

What is a plasmid?

Answer 6

One or more rings of DNA found in some bacterial cells.

Contains non-essential genes.

Can be exchanged between cells via conjugation.

Question 7

Describe the structure of a bacterial cell wall and slime capsule

Answer 7

Peptidoglycan (murin) cell wall provides mechanical strength.

May be coated by slime layer to prevent dessication, adhere cells and provide nutrients.

Question 8

Outline the process of gram staining

Answer 8

1. Stain culture with crystal violet. Remove and rinse with water.
2. Add iodine solution and remove after one minute.
3. Add alcohol.
4. Counterstain with red safranin for one minute.
5. Dry and examine sample under microscope.

Question 9

Describe gram positive cell walls

Answer 9

Thick peptidoglycan layer (insoluble in alcohol).

Purple under microscope when stained

Question 10

Describe gram negative cell walls

Answer 10

Thin peptidoglycal layer with outer lipopolysaccharide membrane (alcohol-soluble).

Red under microscope when stained (as they hold safranin counterstain).

Question 11

Why do Gram positive and Gram negative bacteria respond differently to certain antibiotics?

Answer 11

Antibiotics that inhibit peptidoglycan formation e.g. penicillin work on Gram positive bacteria. Since Gram negative bacteria have an outer membrane and a much thinner peptidoglycan layer, they aren’t affected.

Question 12

Compare ribosome in eukaryotic and prokaryotic cells

Answer 12

Formed of protein and rRNA.

Have a large subunit which joins amino acids and small subunit with mRNA binding site.

Question 13

Contrast ribosomes in eukaryotic and prokaryotic cells

Answer 13

Large subunit eukaryotic: 80S (bigger)

Large subunit prokaryotic: 70S (smaller)

Question 14

What is a eukaryote?

Answer 14

Eukaryotic cells have a nucleus and membrane bound organelles - e.g. All plants, animals, fungi, algae and protists

Question 15

Describe the structure of the nucleus

Answer 15

Surrounded by nuclear envelope, a semi-permeable double membrane.

Nuclear pores allow substances to enter/exit.

Dense nucleolus made of RNA and proteins assembles ribosomes.

Question 16

Describe the function of the nucleus

Answer 16

Contains DNA coiled around chromatin into chromosomes.

Controls cellular processes: gene expression determines specialisation and site of mRNA transcription, mitosis, semiconservative replication.

Question 17

Describe the structure and function of the endoplasmic reticulum (ER)

Both smooth and rough

Answer 17

Cisternae: network of tubules and flattened sacs extends from cell membrane and connects to nuclear envelope.

Rough ER: many ribosomes attached for protein synthesis and transport.

Smooth ER: lipid synthesis.

Question 18

Describe the structure of the mitochondrion

Answer 18

Surrounded by double membrane folded inner membrane forms cristae: site of electron transport chain.

Fluid matrix: contains mitochondrial DNA, respiritory enzymes, lipids, proteins.

Question 19

Describe the structure of the chloroplast

Answer 19

• Vesicular plastid with double membrane
• Thylakoids: flattened discs stack to form grana; contain photosystems with chlorophyll
• Intergranal lamellae: tubes attach thylakoids in adjacent grana
• Stroma: fluid filled matrix

Question 20

State the function of the mitochondria

Answer 20

Site of aerobic respiration to produce ATP

Question 21

State the function of the chloroplasts

Answer 21

Site of photosynthesis to covert solar energy to chemical energy

Question 22

Describe the structure and function of the Golgi apparatus

Answer 22

Planar stack of membrane-bound, flattened sacs cis face aligns with rER:
molecules are processed in cristernae vesicles bud off trans face via exocytosis

• Modifies and packages proteins for transport
• Synthesises gylcoproteins

Question 23

Describe the structure and function of the lysosome

Answer 23

Sac surrounded by a single membrane embedded H⁺ pump maintains acidic conditions contains digestive hydrolase enzymes gylcoprotein coat protects cell interior

• Digests contents of phagosome
• Exocytosis of digestive enzymes

Question 24

Describe the structure and function of a plant cell wall

Answer 24

• Made of cellulose microfibrils for mechanical support
• Plasmodesmata form part of apoplast pathway to allow molecules to pass between cells
• Middle lamella separates adjacent cell walls

Question 25

Describe the structure and function of the cell vacuole in plants

Answer 25

Surrounded by a single phospholipid membrane called a tonoplast.

Store cell sap, which contains mineral ions, water enzymes, soluble pigments.

Question 26

Describe the function of the cell vacuole in plants

Answer 26

• Controls turgor pressure
• Absorbs and hydrolyses potentially harmful substances to detoxify cytoplasm

Question 27

Describe the structure and function of animal vacuoles

Answer 27

More commonly reffered to as vesicles.

Temporary membrane-bound sacs containing water and chemicals.

Numerous and much smaller than in plants.

Question 28

Describe the structure and function of centioles

Answer 28

Spherical group of 9 tubules arranged in triples.

Located in centrosomes.

Migrate to opposite poles of cell during prophase and spindle fibres form between them.

Question 29

Why do samples need to be stained for microscopy?

Answer 29

Stains bind to structures.
Heavy metals: electron microscopes
Coloured dye: optical microscopes

Facillitates absorbtion of electrons/ wavelengths of light to produce image. Contrast between heavily and lightly stained areas distinguishes structures.

Question 30

Define magnification

Answer 30

Factor by which the image is larger than the actual specimen

Question 31

Define resolution

Answer 31

Smallest separation distance at which two separate structures can be distinguished from one another

Question 32

State the magnification and resolution of a compound optical microscope

Answer 32

Magnification: x2000

Resolution: 200nm

Question 33

How does an optical microscope work?

Answer 33

1. Lenses focus rays of light and magnify the view of a thin slice of specimin
2. Different structures absorb different wavelengths of light
3. Reflected light is transmitted to the observer via the objective lens and eyepiece

Question 34

What limits the resolution of an optical microscope?

Answer 34

Diffraction of light.

Any structure closer than half the wavelength of light cannot be distinguished as separate.

Question 35

Describe how a transmission electron microscope (TEM) works

Answer 35

1. Pass a high energy beam of electrons through thin slice of specimin
2. More dense structures appear darker since they absorb more electons
3. Focus image onto fluorescent screen or photographic plate using magnetic lenses

Question 36

State the magnification and resolution of a TEM

Answer 36

Magnification: x500,000

Resolution: 0.5nm

Question 37

Describe how a scanning electron microscope (SEM) works

Answer 37

1. Focus a beam of electrons onto a specimin’s surface using electromagnetic lenses
2. Reflected electrons hit a collecting device and are amplified to produce an image on a photographic plate

Question 38

State the magnification and resolution of an SEM

Answer 38

Magnification: x500,000

Resolution: 3-10 nm

Question 39

Explain how to use the eyepiece graticule and stage micrometer to measure the size of a structure

Answer 39

1. Place the micrometer on stage to calibrate eyepiece graticule
2. Line up scales on graticule and micrometer. Count how many divisions are in 100μm on the micrometer
3. Length of 1 eyepiece division = 100μm / number of divisions
4. Use calibrated values to calculate actual length of structures

Question 40

State an equation to calculate the actual size of a structure from microscopy

Answer 40

Actual size = Image size / Magnification

I AM triangle to remember easily