Cell Ultrastructure

Question 1

What is the function of:

a) Nucleus
b) Mitochondria
c) Ribosomes
d) Rough endoplasmic reticulum
e) Smooth endoplasmic reticulum
f) Golgi apparatus
g) Lysosomes
h) Plasma membrane
i) Cytoskeleton
j) Centrioles
k) Chloroplasts

Answer 1

a) Controls all the activities of the cell through protein synthesis & contains the genetic material as DNA
b) Responsible for the production of ATP - direct source of energy (responsible for respiration)
c) Conduct protein synthesis
d) Has ribosomes & provides a large SA for plotein synthesis and glycoproteins (protein + sugar)
e) Synthesises, stores & transports lipids & proteins
f) Produces secretory enzymes & carbs. Transports, modifies and stored lipids. Adds carbs to proteins to make glycoproteins
g) Formed from golgi. Contains digestive enzymes that can be released to destroy unwanted/ dead materials
h) Surrounds cells, forming boundary between the cytoplasm and the environment, controlling substances moving in & out of the cell
i) Holds & maintains the structure of the cell membrane
j) Used for cell division by generating the spindle fibres, and responsible for separating chromosomes in mitosis
k) Capturing sunlight to use in photosynthesis

Question 2

What is the function of the nucleus?

Answer 2

Controls all the activities of the cell through protein synthesis & contains the genetic material as DNA

Question 3

What is the function of the mitochondria?

Answer 3

Responsible for the production of ATP - direct source of energy (responsible for respiration)

Question 4

What is the function of ribosomes?

Answer 4

Conduct protein synthesis

Question 5

What is the the function of rough endoplasmic reticulum?

Answer 5

Has ribosomes & provides a large SA for plotein synthesis and glycoproteins (protein + sugar)

Question 6

What is the function of smooth endoplasmic reticulum?

Answer 6

Synthesises, stores & transports lipids & proteins

Question 7

What is the function of the golgi apparatus?

Answer 7

Produces secretory enzymes & carbs. Transports, modifies and stored lipids. Adds carbs to proteins to make glycoproteins

Question 8

What is the function of lysosomes?

Answer 8

Formed from golgi. Contains digestive enzymes (lysozymes) that can be released to destroy unwanted/ dead materials

Question 9

What is the function of the plasma membrane?

Answer 9

Surrounds cells, forming boundary between the cytoplasm and the environment, controlling substances moving in & out of the cell

Question 10

What is the function of chloroplasts?

Answer 10

Capturing sunlight to use in photosynthesis

Question 11

What is the function of centrioles?

Answer 11

Used for cell division by generating the spindle fibres, and responsible for separating chromosomes in mitosis

Question 12

What is the function of the cytoskeleton?

Answer 12

Holds & maintains the structure of the cell membrane

Question 13

Talk about the nucleus structure

Answer 13

Spherical, 10-20 micrometres
Nuclear envelope is a double membrane surrounding it. The outer membrane is continuous with endoplasmic reticulum & has ribosomes close to its surface
Nuclear pores allow large molecules in and out
Contains the nucleolus - small, darker spherical body within.
Chromatin (uncoiled, invisible chromosomes. Chromosomes only formed in mitosis) in the nucleus

Question 14

What is the function of the nucleolus?

Answer 14

Manufactures ribosomal RNA and ribosomes. Found as a small, dark spherical body in the nucleus

Question 15

What is the nuclear envelope?

Answer 15

A double membrane surrounding the nucleus. Outer membrane has endoplasmic retuculum & ribosomes on its surface

Question 16

Talk about the structure of mitochondria

Answer 16

Rod shaped, 1-10 micrometres.
Have a double membrane, inner membrane folded into a cristae. Matrix is the space in the mitochondria
It’s the site of oxidative phosphorylation (getting energy from oxygen to do ADP + P = ATP)

Question 17

Talk about the structure of a ribosome

Answer 17

Made of 2 sub units (looks like a snow man)!
Each unit contains ribosomal RNA (r RNA) & protein.
80 S in eukaryotic cells, 70 S in prokaryotic cells (bigger in eukaryotes)

Question 18

Talk about:

a) Rough endoplasmic reticulum
b) Smooth endoplasmic reticulum

Answer 18

a) Has ribosomes on its surface. Provides a large surface area for protein synthesis & glycoproteins
b) Lacks ribosomes. Only synthesises, stores & transports lipids & carbs
Both are found continuous with the nuclear membrane

Question 19

Talk about the golgi apparatus structure

Answer 19

Stack of flattened membranous discs (like a WiFi symbol, golgi vesicles/ lysosomes - blobs - coming off it)
Adds carbs & proteins to make glycoproteins.
Produces secretory enzymes & carbs
Transports, modifies and stores lipids

Question 20

Talk about lysosomes structure

Answer 20

Formed from budding of the golgi apparatus
Contains digestive enzymes, up to 1 micrometre
Has a phospholipid layer
Single membrane
Breaks down material outside of cell/ ingested by phagocytic cells/ worn out organelles/ dead cells

Question 21

Talk about the plasma membranes’ structure

Answer 21

Surrounds cells, forming a boundary.

Lined with phospholipids & proteins to control what enters & stays out

Question 22

Talk about the structure of the cytoskeleton

Answer 22

Holds the structure of the cell membrane - surrounds the cell

Question 23

Talk about the structure of the centrioles

Answer 23

Close to the nucleus - in the centre, a dense area of cytoplasm called the centrosome. Each cell only has a pair of centrioles
Cylindrical - at right angles to each other, create the spindle fibres in mitosis

Question 24

|What is the centrosome?

Answer 24

A dense area of cytoplasm where the centrioles are.

Question 25

Talk about the structure of the chloroplasts

Answer 25

Have stacked discs called thylakoid
Stack of thylakoids is a granum
Stroma fills the rest of it
Pigment is chlorophyll - absorbs the sunlight

Question 26

What is a stack of thylaoids called?

Answer 26

Granum - in the chloroplasts

Question 27

What is centrifugation?

Answer 27

A way of separating organelles creating pure samples

Question 28

What is the type of centrifugation we have to worry about called?

Answer 28

Differential centrifugation. Separated based on WEIGHT

Question 29

What is a homogenate?

Answer 29

The resultant fluid of blending a substance so all the organelles are free from the cells

Question 30

Talk through each stage of differential centrifugation

Answer 30

1) Homogenation - cells broken by homogeniser (blender, can just be a mortar and pestle), releasing the organelles. The resultant fluid is called the homogenate, which is filtered to remove large debris (fine cloth used)
2) Must be cold (2C), buffered & in isotonic salt solution to freeze cell from enzyme reactions & osmosis
3) Put the homogenate into a centrifuge tube. The first sample is sampled at a low speed for a short time. The heaviest (nucleus, around 10 mins) forms a layer at the bottom
4) The supernatant (leftovers from first sample) put in a new centrifuge tube & spun at a higher speed for longer. Leaves 2nd heaviest - mitochondria & lysosomes (around 15 mins)
5) Repeat, leaving the rough endoplasmic reticulum & ribosomes (30 mins roughly)

Question 31

What does the homogeniser not damage organelles?

Answer 31

Because they are too small

Question 32

Why must the homogenate be kept

a) Cold?
b) Buffered?
c) In an isotonic salt solution?

Answer 32

a) To stop all cell activity - no kinetic energy so enzymes inactive, so stops enzyme based reactions
b) To maintain pH, so enzymes and proteins stay unchanged
c) Same concentration as cells, so removes osmotic effects - the water stays

Question 33

What is are the 3 heaviest organelles?

Answer 33

Nucleus
Mitochondia (&lysosomes)
Rough endoplasmic reticulum (& ribosomes)

Question 34

What is the supernatant?

Answer 34

After centrifuging the first sample, the homogenate left over is the supernatant. Still contains a mix of organelles, and centrifuging it again will create a new pure sample.