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Biology > Topic 3 - Cell structure > Flashcards

Topic 3 - Cell structure Flashcards

1
Q

Principles of optical microscopes

A

Simple convex glass lenses used in pairs in a compound light microscope to focus an object at a short distance by 1st lens, then magnified by 2nd lens

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2
Q

Pros and cons of optical microscope

A

Pros:
- Cheap
- Images in colour
- No training required
- Live specimens

Cons:
- Low magnification
- Low resolution
- 2D images

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3
Q

Principles of transmission electron microscope

A
  1. Electron gin produces e- beam, focused onto the specimen by a contender electromagnet
  2. Beam passes through a thin section of the specimen from below. Parts absorb e- and appear dark; others let e- pass through and appear bright - produces image on screen - photomicrograph
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4
Q

Pros and cons of transmission electron microscope

A

Pros:
- High resolution images
- High magnification
- Visible internal structures

Cons:
- Expensive
- Training is required
- No colour images
- 2D images
- Only thin specimens

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5
Q

Principles of scanning electron microscope

A
  1. Beam of e- directed onto surface of specimen - passed back and forth across specimen
  2. e- scattered by specimen - scattering pattern analysis allows us to get a 3D image
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6
Q

Pros and cons of scanning electron microscope

A

Pros:
- 3D images
- High magnification
- High resolution
- Thick specimens

Cons:
- Expensive
- Training is required
- No colour images

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7
Q

How do you prepare a slide for an optical microscope

A
  1. Pipette a drop of water onto a slide
  2. Use tweezers to place a thin section of your specimen on top of the droplet
  3. Add a drop of a stain
  4. Add a cover slip - remove all air bubbles
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8
Q

What is the difference between magnification and resolution?

A

Magnification: Increasing the size of an image. Up until the limit of resolution, an increase in magnification = an increase in detail

Resolution: minimum mistaken apart that two objects can be for them to appear separate items

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9
Q

What is the formula to calculate magnification

A
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10
Q

Can you describe the principles of cell fractionation and ultracentrifugation in separating cell components?

A
  1. Homogenisation
    - Tissue is broken up in a cold, isotonic buffer solution to release the organelles into a solution
  2. Filtration
    - The homogenised cell solution is filtered through a gauze
    - This separates any large cell debris
  3. Ultracentrifugation
    - The cell fragments are poured into a test tube and placed in a centrifuge and spun at a low speed
    - a thick sediment - the pellet - is at the bottom of the tube and the fluid above is the supernatant
    - The supernatant is drained into a new tube and spun again at a higher speed
    - a new pellet forms and again, the supernatant is drained off and spun again at an even higher speed
    - this process is repeated at higher speeds each time until all the organelles are separated out
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11
Q

Why is a cold, isotonic buffer needed

A

Cold - to reduce enzyme activity that could break down organelles

Isotonic - same water potential as tissue sample - to prevent water moving in or out of the cells by osmosis, causing lysis

Buffered - to prevent changes in pH which could affect/denature enzymes

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12
Q

How are organelles separated out during centrifugation?

A

They are separated in order of mass and the order is usually
Nuclei
Mitochondria
Lysosomes
Endoplasmic reticulum
Ribosomes

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13
Q

Distinguishing features of eukaryotic cells

A
  • Cytoplasm contains membrane bound organelles
  • DNA is enclosed in a nucleus
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14
Q

general structure of animal cell

A
  • Mitochondrion
  • nucleus
  • Nucleolus
  • RER
  • SER
  • Golgi apparatus
  • Golgi vesicle
  • Cytoplasm
  • Cell surface membrane
  • Ribosomes
  • Lysosome
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15
Q

General plant structure

A

Same as animal
- Chloroplast
- Cell vacuole
- Cell wall

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16
Q

Cell surface membrane

A
  • Selectively permeable barrier between the cell and its environment –> enables control of passage
  • Also contains molecules / receptors / antigens on surface allowing cell recognition / signalling
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17
Q

What does the nucleus consist of

A

Nuclear envelope:
- Double membrane
- Has nuclear pores which allow substances e.g. mRNA to move between nucleus and cytoplasm

Nucleolus:
- Makes ribosomes

Nucleoplasm: granular jelly like material that makes up the bulk of the nucleus

Protein bound, linear DNA:
- Chromatin = condensed
- Chromosome = highly condensed

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18
Q

Ribosomes

A

Two subunits = large subunit and small subunit, each of which contains ribosomal RNA and protein
- Not surrounded by a membrane but can be attached to RER
- Site of protein synthesis - translation

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19
Q

smooth endoplasmic reticulum

A
  • No ribosomes
  • Synthesises and processes lipids
  • Synthesises and processes carbohydrates
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20
Q

Rough endoplasmic reticulum

A
  • Ribosomes on surface synthesise proteins
  • Proteins processed / folded and transport inside RER
  • Proteins packaged into vesicles for transport e.g. to Golgi apparatus
21
Q

Golgi apparatus and vesicles

A

Golgi apparatus = flattened membrane sacs
- Modifies/processes protein from RER
- e.g. protein + carbohydrate –> gylcoproteins
- Packages them into Golgi vesicles
- Produces lysosomes (a type of Golgi vesicle)

Golgi vesicle = small membrane sac
- Transports proteins / lipids to their required destination
- e.g. to the cell-surface membrane

22
Q

Lysosomes

A
  • Contains/releases lysozymes (hydrolytic enzymes)
  • To break down / hydrolyse pathogens
  • Or worn out cell components
23
Q

Mitochondria

A

Components of the mitochondria:
- Outer membrane
- Cristae - inner membrane fold
- Matrix, containing: small / 70s ribosomes, circular DNA

  • Site of aerobic respiration
  • To produce ATP for energy release
24
Q

Chloroplasts

A

Components of the chloroplast:
- Double membrane
- Stroma, containing: Thylakoid membrane, Small 70s ribosomes, Circular DNA, Starch granules / lipid droplets
- Lamella - thylakoid linking grana
- Grana - stacks of thylakoid

  • Absorbs light energy for photosynthesis
  • To produce organic substances e.g. carbohydrates / lipids
25
Q

Cell wall

A
  • Formed outside of the cell membrane
  • Composed mainly of cellulose (a polysaccharide) in plants and algae
  • Composed of chitin (a nitrogen containing polysaccharide) in fungi
  • Provides mechanical strength to the cell
  • So prevents cell changing shape or bursting under pressure due to osmosis
  • Note = it is permeable to most substances (unlike the cell-surface membrane)
26
Q

Cell vacuole

A
  • Maintains turgor pressure in the cell, supporting the plant
  • Contains cell sap - s store of sugars, amino acids, pigments and any waste chemicals
27
Q

Organisation in complex multicellular organisms

A
  • In complex multicellular organisms, eukaryotic cells become specialised for specific functions
  • Specialised cells are organised into tissues, tissues into organs and organs into systems
28
Q

Tissue

A

Group of specialised cells with a similar structure working together to perform a specific function, often with the same origin

29
Q

Organ

A

Aggregations of tissues performing specific functions

30
Q

Organ system

A

Group of organs working together to perform specific functions

31
Q

Explaining adaptations of specialised eukaryotic cells

A
  • Many cells need a Hugh rate of protein production - e.g. antibodies, enzymes, hormones:
    Many ribosomes and rough endoplasmic reticulum
    For a high rate of protein synthesis
  • Many cells need a high rate of ATP production - e.g. for active transport or muscle contraction:
    Many mitochondria
    For a high rate of aerobic respiration / ATP production
32
Q

Distinguishing features of prokaryotic cells

A
  • Cytoplasm lacks membrane-bound organelles
  • So genetic material not enclosed in a nucleus
33
Q

Structure of a general prokaryotic cell

A
34
Q

Examples of prokaryotic organisms:

A
  • Bacteria
  • Archaea
35
Q

Contrasting eukaryotic and prokaryotic cells

A
36
Q

Viruses: acellular and non living

A
  • Acellular - not made of or able to be divided into cells
  • Non-living - unable to reproduce without a host cell, no metabolism
37
Q

General structure of a virus particle

A
  • Nucleic acids surrounded by a capsid (protein coat)
  • Attachment proteins allow attachment to specific host cells
  • No cytoplasm, ribosomes, cell wall, cell surface membrane etc.
  • Some also surrounded by a lipid envelope
38
Q

Interphase

A
  • S phase - DNA replicates semi-conservatively leading to two sister chromatids
  • G1 and G2 - number of organelles and volume of cytoplasm increases; protein synthesis; ATP content increased
39
Q

Mitosis

A
  • Parent cell divides = two genetically identical daughter cells, containing identical/exact copies of DNA of the parent cell
  • Stages - ‘PMAT’
40
Q

Prophase

A
  • Chromosomes condense, becoming shorter and thicker = appear as two sister chromatids joined by a centromere
  • Nuclear envelope breaks down and centrioles move to opposite poles forming spindle network
41
Q

Metaphase

A
  • Chromosomes align along equator
  • Spindle fibres attach to chromosomes by centromeres
42
Q

Telophase

A
  • Chromosomes uncoil, becoming longer and thinner
  • Nuclear envelope reforms = two nuclei
  • Spindle fibres and centrioles break down
42
Q

Anaphase

A
  • Spindle fibres contract, pulling sister chromatids to opposite poles of the cell
  • Centromere divides
43
Q

Cytokinesis

A
  • The division of the cytoplasm, usually occurs, producing two new cells
44
Q

The importance of mitosis in the life of an organism

A

Parent cell divides to produces 2 genetically similar identical daughter cells for:
- Growth of multicellular organisms by increasing cell number
- Repairing damaged tissues / replacing cells
- Asexual reproduction

45
Q

Recognising different stages of the cell cycle

A
  • Interphase - C –> no chromosomes visible (visible nucleus)
  • Prophase - B –> Chromosomes visible but randomly arranged
  • Metaphase - D –> chromosomes lined up of the equator
  • Anaphase - E –> chromatids (in two sets) being separated to opposite poles by spindles, V shape shows sister chromatids have been pulled apart at their centromeres
  • Telophase - A –> chromosomes in two sets, one at each pole
46
Q

Many cancer treatments are directed at controlling the rate of cell division

A

Disrupt the cell cycle - cell division / mitosis slows - tumour growth slows
- Prevent DNA replication –> prevent / slows down mitosis
- Disrupts spindle activity / formation –> chromosomes cant attach to spindle by their centromere –> sister chromatids cant be pulled to opposite poles of the cells –> prevents / slows mitosis

Con = Disrupt cell cycle of normal cells too, especially rapidly dividing ones e.g. cells in hair follicles
Pro = Drugs more effective against cancer cells because dividing uncontrollably / rapidly

47
Q

Prokaryotic cells replicate by binary fission

A
  • Circular DNA and plasmids replicate ( circular DNA replicates once, plasmids can be replicated many times)
  • Cytoplasm expands (cells get bigger) as each DNA molecule moves to opposite poles of the cell
  • Cytoplasm divides
  • = two daughter cells, each with a single copy of DNA and a variable number of plasmids
48
Q

Viral replication

A

Viruses don’t undergo cell division because they are non-living
1. Attachment protein binds to complementary receptor protein on surface of host cell
2. Inject nuclei acid (DNA/RNA) into host cell
3. Infected host cell replicates the virus particles

Biology (20 decks)

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