Cell fractionation/Microscopes/ Mitosis

Question 1

What is the equation of magnification?

Answer 1

magnification = size of image/ size of real object

Question 2

What is cell fractionation?

Answer 2

the process where cells are broken up and the different organelles they contain are separated out

Question 3

Describe briefly the process of Cell fractionation

Answer 3

the tissue is placed in a cold buffered solution of the same water potential as the tissue. It then goes through homogenisation and ultracentrifugation

Question 4

Why is the tissue in Cell fractionation put in a cold, buffered solution (with the same water potential?

Answer 4

cold = reduce enzyme activity to prevent self-digestion of organelles

same water potential = prevent organelles from bursting or shrinking as a result of osmotic gain or loss of water

buffered= so that the pH does not fluctuate. Any change to the pH could alter the structure of the organelles or affect the functioning of enzymes

Question 5

What happens during homogenisation?

Answer 5

• Cells are broken up by a homogenizer (blender), which releases the organelles from the cell
• this results in homogenate, which is then filtered to remove any complete cells and large pieces of debris

Question 6

What is ultracentrifugation?

Answer 6

the process by which the fragments in the filtered homogenate are separated in a centrifuge.

Question 7

What happens during ultracentrifugation?

Answer 7

• the tube of filtrate is placed in the centrifuge and spun at a slow peed
• the heaviest organelles, the nuclei, are forced to the bottom of the tube, where they form a thin pellet
• the fluid at the top of the tube (supernatant) is removed, leaving just the sediment of the nuclei
• the supernatant is transferred to another tube and spun in the centrifuge at a faster speed than before
• the next heaviest organelles, the mitochondria, are forced to the bottom of the tube
• at each increase in speed, the next heaviest organelle is sedimented and separated out.

Question 8

Tell me about light microscopes

Answer 8

• use light to form an image
• The relatively long wavelength of light rays means that light microscopes can only distinguish between two objects if they are 0.2 micrometers or further apart. = poor resolution
• smaller magnification than electron microscopes
• image in colour

Question 9

Tell me about electron microscopes

Answer 9

• Use beam of electrons instead of light rays
• higher resolution due to the electron beam having a short wavelength
• Electrons are negatively charged, so the beam can be focused using electromagnets
• Electrons are absorbed or deflected by molecules in the air = must be in a vacuum

Question 10

How do Transmission electron microscopes (TEMs) work?

Answer 10

it consists of an electron gun that produces a beam of electrons that is focused onto the specimen by a condenser electromagnet.

The beam passes through a thin section of the specimen, which absorbs some electrons and lets some through, producing a black and white image

( the specimen is penetrated from below)

Question 11

Pros and cons of TEM

Answer 11

• has a magnification up to 1 million and a resolution of 0.1nm
• can examine really small organelles, as well as virus and bacteria
• resolving power sometimes not achieved due to difficulties preparing the specimen and a higher energy electron beam being needed, which could destroy the specimen
• the whole system in a vacuum = needs to be dead
• a complex staining process is required and the image isn’t in colour
• the specimen needs to be extremely thin = 2D image only
• may contain artefacts (things that are a result from the way the specimen was prepared)

Question 12

How do scanning electrons microscope work?

Answer 12

Directs a beam of electrons on the surface of the specimen from above, the beam is then passed back and forth across a portion of the specimen in a regular pattern.

The electrons are scattered by the specimen and the pattern of the scattering depends on the contours of the specimen surface.

A 3D image is produced by a computer analysis of the pattern of scattered electrons and secondary electrons produced.

Question 13

Pros and cons of SEM

Answer 13

Pros :

• 3D image is produced
• can be used on thick specimens

Cons:

• do not produce a colored image
• has a lower resolving power (20nm)
• can’t see the internal structure of the cell, because it scans the surface of the object.

Question 14

What are the stages of the cell cycle?

Answer 14

Interphase, mitosis, cytokinesis

Question 15

What happens during the interphase? (describe all the phases within this phase

Answer 15

the cell increases in mass and size and carries out its normal cellular functions

G1 phase = Cells make the RNA, enzymes, and other proteins required for growth (high amount of protein synthesis). Make organelles and grow bigger

S phase = DNA replicated (chromosomes will now consist if two sister chromosomes are held together by chromatids**)**

G2 phase = the cell keeps growing until all of the organelles have duplicated. Proteins needed for cell division are needed

The mitochondria produce more ATP which will provide the energy for cell division

Question 16

What are checkpoints in the cell cycles and when does it happen?

Answer 16

There are two ‘checkpoints’ in the cell cycle - one before S phase and one straight after S phase.

During these checkpoints, the cell is checking its DNA for errors.

This minimises the chances of duplicating any mutated DNA into the replicated cell.

Question 17

What is mitosis?

Answer 17

when the eukaryotic cell divides to produce two daughter cells, each with the identical copies of DNA produced by the parent cell during DNA replication

Question 18

What are the 5 stages of mitosis in order?

Answer 18

Interphase, prophase, metaphase, anaphase and telophase

Question 19

What happens during the prophase?

Answer 19

chromosomes condense getting shorter and fatter ( they become visible)

centrioles move to the opposite poles of the cell. this is where protein spindle fibers are released

The nucleolus disappears and the nuclear envelope breaks down bn

Question 20

What happens during the metaphase?

Answer 20

there is no longer a nucleus in the cell, the centrioles move to opposite poles and release spindle fibers

the chromosomes align themselves at the equator of the cell each with a pair of sister chromatids

spindle fibers attach to either the chromatids or centromere

Question 21

What happens during the anaphase?

Answer 21

A

the chromosome divide, separating each pair of sister chromatids.

the spindles contract towards the centrioles so the centromere breaks due to the tension created

resulting in the chromatids separating by being pulled to opposite poles of the cell

this stage requires a lot of ATP from respiration

Question 22

what do v-shaped chromosomes show?

Answer 22

that the chromatids have been pilled apart at their centromeres

Question 23

What happens during the telophase?

Answer 23

the chromatids reach the opposite poles on the spindle

they uncoil and become long and thin again

they’re now called chromosomes again

a nuclear envelope forms around each group of chromosomes, so there are now two nuclei

Division of the cytoplasm (cytokinesis, which starts in anaphase) finishes in telophase

there are now two daughter cells that are genetically identical to the original cell and o each other.

mitosis is finished and each daughter cell starts the interphase part of the cell cycle to get ready for the next round of mitosis

Question 24

Describe what happens in binary fission?

Answer 24

circular DNA molecule replicates and both copies attach to the cell membrane

the plasmids also replicate

the cell membrane begins to grow between the two DNA molecules and begins to pinch inward, dividing the cytoplasm into two

A new cell wall forms between the two molecules of DNA, dividing the original cell into two identical daughter cells, each with a single copy of the circular DNA and a variable number of copies of the plasmids

Question 25

Why can’t viruses undergo cell division and how to they replicate?

Answer 25

because they are non-living.

They replicate by attaching to their host cell with the attachment proteins on their surface.

Then, they inject their nucleic acid into the host cell.

Genetic information on the injected viral nucleic acid then provides the instructions for the host cell’s metabolic processes to start producing the viral components, nucleic acid, enzymes, and structural proteins, which are then assembled into new viruses.

Question 26

What is the importance of mitosis?

Answer 26

• growth
• repair
• reproduction