5. Cell Organelles

Question 1

Why are cells typically very small?

Answer 1

1. Greater SA:Vol -> enables food and waste to be imported + exported efficiently.
2. Small structures have greater integrity.

Question 2

What are the major classes of cells and what are their differences? How do they reproduce?

Answer 2

Prokaryotic (bacteria) - singled celled, no nucleus, no membrane bound organelles. Reproduce by binary fission.
Eukaryotic - single nucleus, membrane bound organelles. Reproduce mostly by sexual or asexual budding.

Question 3

What are the kingdoms of eukaryotic life?

Answer 3

1. Plantae
2. Animalia
3. Protista (single celled)
4. Fungi

Question 4

LIST organelles do ANIMAL cells have that plants cells don’t

Answer 4

List: lysosomes, flagella, centrioles.

Question 5

LIST organelles do PLANT cells have that animal cells don’t?

Answer 5

List: tough cell wall, plasmodesmata, central vacuoles, chloroplasts, amyloplasts.

Question 6

LIST techniques for studying cells

Answer 6

Light microscopy (can use a stain), super-resolution microscopy, electron microscopy, X-ray crystallography, synchrotron.

Question 7

What are limitations of light microscopy?

Answer 7

1. Limit of diffraction. (Abbe’s limit)

2. Need contrast to see difference between two objects (solved by staining)

Question 8

What kind of stains are there for light microscopy?

Answer 8

Methylene blue - stains nuclei of animal cells
Eosin - stains cell walls, cytoplasmic material and extracellular structures red or pink.
Some stains fluoresce when excited by UV.

Question 9

What is super-resolution microscopy?

Answer 9

Employs ‘selectively depleted’ fluorescence and multiple lenses to capture 2D and 3D images at greater than 0.2um detail.

Question 10

What is electron microscopy?

Answer 10

Uses a stream of electrons to create extremely high magnification images. Must be viewed under vacuum (sampels are dead), and have to be coated in heavy metal. Two kinds: SEM and TEM.

Question 11

What is difference between SEM and TEM?

Answer 11

Scanning EM - samples reflect electron beam back to detector. Good 3D shape of sample.

Transmission EM - electron beam passes through sample -> best resolution.

Question 12

How does X-ray crystallography work?

Answer 12

Works by scattering X-rays are regions of electron density within sample. The more electrons = more scattering. Proteins/cell components are isolated, purified then crystallised before X-Ray diffraction.

Question 13

How do you study organelles?

Answer 13

Isolate it. If sturdy, use tissue grinder.

Cell press - uses sudden change in pressure to cause cells to pop under own internal pressure.

Question 14

List membrane bound organelles (7 items)

Answer 14

• Nucleus
• Nucleoid
• Mitochondria
• Endoplasmic reticulum
• Golgi apparatus
• Lysosome
• Vacuole

Question 15

List non-membrane bound organelles (4 items)

Answer 15

• Ribosome
• Cytoskeleton
• Flagella
• Centriole

Question 16

What is the nucleus?

Answer 16

Stores genetic information and where ribosomes are assembled. Porous and continuous with ER.

Question 17

What is nucleoid?

Answer 17

In prokaryotes. Poorly defined region in centre where single circular chromosomes of bacteria are kept.

Question 18

What is mitochondria?

Answer 18

Organelle that provides eukaryotes ATP via aerobic respiration. Has outer and inner membrane, separated by intermembrane space. Inner membrane has mitochondrial matrix. Own DNA from maternal line.

Question 19

What is ER?

Answer 19

ER: Folds of membrane bilayer - one of the sites of protein synthesis. Rough ER = close to nucleus, . Continuous to RER = Smooth ER - site of many enzyme reactions and reservoir for Ca2+.

Question 20

What is Golgi apparatus?

Answer 20

Downstream of ER, also protein modification and trafficking. 3 types: cis (closest to nucleus), medial, trans (further from nucleus).

Question 21

What is lysosome?

Answer 21

Helps breakdown large molecules like protein and polysaccharide. Has digestive enzymes and low pH. Repairs plasma membrane.

Question 22

What is vacuole?

Answer 22

Large central sac of plant and fungal cells. Storage of harmful substances or water products. Often acidic pH.

Question 23

What is ribosome?

Answer 23

Organelle. Read mRNA to make polypeptides. 2 subunits.

Question 24

What is cytoskeleton?

Answer 24

Network of protein tubes that give cell structure. 3 kinds: microtubules, intermediate filaments and micro- or actin filaments.

Question 25

What is flagella?

Answer 25

Fine flexible rods sticking out of eukaryotic/bacteria cells. Moves cell or wash liquid over cell.

Question 26

What is centriole?

Answer 26

Protein clusters, made of ring of microtubule triplets. A pair makes the centromere. During cell division, no. of centrioles double and migrate to 2 poles of cell. Serve as anchors so spindle fibres have something to pull against.

Question 27

What is the theory of endosymbiosis?

Answer 27

An ancestral proto-eukaryotic cell engulfed bacteria, and existed in a symbiotic relationship with host cell. After many generations, the bacterial cell became dependent, and the host relied on the products from the symbiont. -> explains residual genomic elements in these organelles. E.g. double membrane around these organelles as ancestral prokaryote would be wrapped in a vesicle when endocytosed.