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Biology AS > Cell structure part 2 > Flashcards

Cell structure part 2 Flashcards

1
Q

What is the object?

A

The material put under the microscope.

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2
Q

What is the image?

A

The appearance of the object when viewed under the microscope.

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3
Q

What is magnification?

A

How many times bigger the image is when compared to the object.

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4
Q

What is the equation for magnification?

A

Magnification = size of image / size of real object

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5
Q

Convert the units of kilometres, metres, millimetres, micrometres and nanometres.

A

Km = 10^3m
m = 1m
mm = 10^-3
μm = 10^-6
nm = 10^-9
x 1000 to get smaller units (e.g. μm to nm, /1000 to go bigger).

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6
Q

What is resolution?

A

The minimum distance apart two objects can be in order for them to appear as separate items.
It depends on the wavelength or form of radiation used.

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7
Q

What is cell fractionation?

A

The process where cells are broken up and the organelles separated out.

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8
Q

What happens before cell fractionation?

A

The tissue is placed in a cold, buffered solution of the same water potential as the tissue.

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9
Q

Why is the solution cold?

A

To reduce enzyme activity that might break down the organelles.

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10
Q

Why is the solution the same water potential?

A

To prevent organelles bursting or shrinking as a result of osmotic gain or loss of water.

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11
Q

Why is the solution buffered?

A

So that the pH does not fluctuate.
Any change in pH could alter the structure of the organelles or affect the functioning of enzymes.

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12
Q

What is the first stage of cell fractionation?

A

Homogenation - cells are broken up by a homogeniser.
This releases the organelles from the cell.
The resultant fluid, homogenate, is then filtered to remove any complete cells and large pieces of debris.

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13
Q

What is the second stage of cell fractionation?

A

Ultracentrifugation - the process that separates the fragments of the homogenate in a centrifuge.
This spins the tubes of homogenate at very high speed to create a centrifugal force.

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14
Q

What is the process of ultracentrifugation?

A

The tube of filtrate is placed in the centrifuge and spun at a slow speed.
The heaviest organelles, the nuclei, are forced to the bottom of the tube, where they form a thin sediment or pellet.
The fluid at the top, supernatant, is removed and transferred to another tube and spun at a faster speed than before.
The next heaviest organelles, the mitochondria, are forced to the bottom.
The process is continued, with increased speed, so the next heaviest organelles are sedimented and separated out.

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15
Q

What is the speed of centrifugation for each organelle?

A

Nuclei - 1000 revolutions per minute.
Chloroplasts
Mitochondria - 3500
Lysosomes - 16500.
Endoplasmic reticulum
Ribosomes

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16
Q

What are the advantages of an electron microscope?

A

The electron beam has a very short wavelength so it can resolve objects very well.
Electrons are negatively charged so the beam can be focused using electromagnets.

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17
Q

What is the resolving power of the best electron microscopes?

A

Resolves objects that are only 0.1nm apart - 2000 times better than a light microscope.

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18
Q

Why do electron microscopes use vacuums?

A

Electrons would be absorbed or deflected by molecules in the air otherwise.

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19
Q

What are the disadvantages of electron microscopes?

A

Living specimens can’t be observed because there is no air in a vacuum.

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20
Q

What are the two types of electron microscope?

A

The transmission electron microscope (TEM)
The Scanning electron microscope (SEM).

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21
Q

How does the TEM work?

A

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.
Parts of the specimen absorb electrons and appear dark.
Other parts of the specimen allow electrons through and so appear bright.
An image appears on the screen and can be photographed to give a photomicrograph.

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22
Q

Why can the highest resolving power of the TEM not always be achieved?

A

The resolving power is 0.1nm but:
Difficulties preparing the specimen limit the resolution.
A higher energy electron beam is required and this may destroy the specimen.

23
Q

What are the limitations of the TEM?

A

The whole system is in a vacuum so living specimens cannot be observed.
A complex ‘staining’ process is required - and even then the image is not in colour.
The specimen must be extremely thin.
The image may contain artefacts - they may appear on the photomicrograph but are not part of the natural specimen.
The image is only 2D.

24
Q

What are artefacts?

A

Things that result from the way the specimen is prepared.

25
Q

What are the limitations of the SEM?

A

The limitations of the TEM apply to the SEM.
However, the specimen does not have to be extremely thin as the electrons do not penetrate.
A 3D image can be produced.

26
Q

How does the SEM work?

A

A beam of electrons is directed onto 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 this depends on the contours of the surface.
A 3-D image is built up by computer analysis of the pattern of scattered electrons and secondary electrons produced.

27
Q

What is the resolving power of the SEM?

A

Around 20nm, which is lower than the TEM, but still 10x better than a light microscope.

28
Q

What is mitosis?

A

A division of a cell that results in two daughter cells having an exact copy of the DNA of the parent cell.

29
Q

How does cell division take place?

A

Either by:
Mitosis - produces 2 daughter cells with the same number of chromosomes as the parent cell and each other.
Meiosis - produces 4 daughter cells, each with half the number of chromosomes of the parent cell.

30
Q

What is interphase?

A

The period following mitosis where the cell is not dividing.
It occupies most of the cell cycle.
Lots of cellular activity, including the replication of DNA.

31
Q

What are the four stages of mitosis?

A

Prophase
Metaphase
Anaphase
Telophase

32
Q

What is prophase?

A

The chromosomes shorten and thicken (condense) and become visible.
Centrioles move to opposite ends of the cell and spindle fibres develop from them.
Collectively, these are called spindle apparatus.
The nucleolus disappears and the nuclear envelope breaks down.
The chromosomes are left freely in the cytoplasm.
The chromosomes are drawn to the equator of the cell by the spindle fibres.

33
Q

What is metaphase?

A

The chromosomes are seen to be made up of 2 chromatids.
Each chromatid is an identical copy of DNA from the parent cell.
The chromatids are joined by the centromere.
The chromosomes are pulled along the spindle apparatus by the centromere and arrange themselves along the equator of the cell.

34
Q

What is anaphase?

A

The centromeres divide into two and the spindle fibres pull the individual chromatids apart.
The chromatids move to their respective poles and are now referred to as chromosomes.
The energy required is provided by the mitochondria, which gather around the spindle fibres.

35
Q

What is telophase?

A

The chromosomes reach their respective poles and become longer and thinner, finally disappearing completely, and leaving widespread chromatin.
The spindle fibres disintergrate and the nuclear envelope and nucleolus re-form.
The cytoplasm divides through cytokinesis.

36
Q

How does cell division happen in prokaryotic cells?

A

Binary fission:
The 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 pinches inwards, dividing the cytoplasm in two.
A new cell wall forms between the two DNA, dividing the cell into two identical daughter cells.
They each have a single copy of the circular DNA and a variable number of copies of the plasmids.

37
Q

What is mitosis used for?

A

Growth
Repair
Reproduction

38
Q

Which cells have a cell cycle?

A

Cells that do not divide continuously but undergo a regular cycle of division separated by periods of growth.

39
Q

What is the first stage of the cell cycle?

A

Interphase - it occupies most of the cycle (about 90%).
It is sometimes known as the resting place as no division takes place.

40
Q

What is the second stage of the cell cycle?

A

Nuclear division - when the nucleus divides either into two or four.

41
Q

What is the third stage of the cell cycle?

A

Cytokinesis - the cytoplasm divides to produce two or four new cells.

42
Q

How long is the cell cycle?

A

Complete cell cycle length varies between organisms.
Typically, a mammalian cell takes about 24 hours, 90% of which is interphase.

43
Q

What is cancer?

A

A group of diseases caused by a growth disorder of cells.
It is the result of damage to the genes that regulate mitosis and the cell cycle.
This leads to uncontrollable growth and division of cells.
The cells can reject apoptosis (the cell naturally killing itself) and keep multiplying.

44
Q

What are tumours?

A

A group of abnormal cells that develop and constantly expand.

45
Q

Where do tumours form?

A

Can develop in any organ in the body but most commonly:
The lungs
Prostate gland
Breasts and ovaries
Large intestine
Stomach
Oesophagus
Pancreas

46
Q

When are tumours cancerous?

A

When they develop from benign to malignant.

47
Q

What are malignant tumours?

A

They grow rapidly
Less compact
More likely to be life-threatening

48
Q

What are benign tumours?

A

Grow more slowly
More compact
Less likely to be life-threatening

49
Q

How is cancer often treated?

A

It often involves killing dividing cells by blocking part of the cell cycle.
The cell cycle is disrupted and cell division, and hence, cancer growth ceases.

50
Q

How is the cell cycle disrupted?

A

The drugs - chemotherapy - prevent the DNA from replicating.
Inhibits the metaphase stage of mitosis by interfering with spindle formation.

51
Q

What is the disadvantage with chemotherapy?

A

They also disrupt the cell cycle of normal cells.
For example, hair-producing cells, that divide rapidly, are also vulnerable to damage, and therefore hair loss is frequent in cancer patients.

52
Q

What is the advantage with chemotherapy?

A

The drugs are more effective against rapidly dividing cells.
Cancer cells have very fast rate of division, so are damaged to a greater degree than normal cells.

53
Q

How do mutations affect mitosis?

A

A mutation to one of the genes controlling mitosis causes uncontrolled mitosis.
The mutant cells are usually structurally and functionally different.
Most mutated cells die.
But those that survive are capable of dividing to form clones of themselves and form tumours.

Biology AS (20 decks)

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