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Biology > Cell Structure > Flashcards

Cell Structure Flashcards

1
Q

Define the terms eukaryotic and prokaryotic cells.

A
  • Eukaryotic: DNA is contained in a nucleus, contains membrane-bound specialised organalles.
  • Prokaryotic: DNA is ‘free’ into cytoplasm, no organelles e.g. bacteria and archaea.
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2
Q

State the relationship between a system and specialised cells.

A

Specialised cells –> tissues that perform a specific function –> organs made of several tissue types –> organ systems.

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3
Q

Describe the structure and function of the cell-surface membrane.

A

‘Fluid mosaic’ phospholipid bilayer with extrinsic & intrinsic proteins embedded.
- isolates cytoplasm from extracellular environment.
- selectively permeable to regulate transport of substances.
- involved in cell signalling / cell recognition.

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4
Q

Explain the role of cholesterol, glycoproteins & glycolipids in the cell-surface membrane.

A
  • Cholesterol; steroid molecule connects phospholipids & reduces fluidity.
  • Glycoproteins; cell signalling, cell recognition (antigens) & binding cells together.
  • Glycoproteins; cell signalling and cell recognition.
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5
Q

Describe the structure of the nucleus.

A
  • Surrounded by nuclear envelope, a semi-permeable double membrane.
  • Nuclear pores allow substances to enter / exit.
  • Dense nucleolus made of RNA & proteins assembles ribosomes.
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6
Q

Describe the function of the nucleus.

A
  • Contains DNA coiled around chromatin into chromosomes.
  • Controls cellular processes: gene expression determines specialisation & site of mRNA transcription, mitosis and semi-conservative replication.
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7
Q

Describe the structure of a mitochondrion.

A
  • Surrounded by double membrane; folded inner membrane forms cristae: site of electron transport chain.
  • Fluid matrix: contains mitochondrial DNA, respiratory enzymes, lipids and proteins.
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8
Q

Describe the structure of a chloroplast.

A
  • Vesicular plastid with double membrane.
  • Thylakoids: flattened discs stack to form Grana: contain photosystems with chlorophyll.
  • Intergranal lamellae: tubes attach thylakoids in adjacent grana.
  • Stroma: fluid-filled matrix.
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9
Q

State the function of mitochondria and chloroplasts.

A
  • Mitochondria: site of aerobic respiration to produce ATP.
  • Chloroplasts: site of photosynthesis to convert solar energy to chemical energy.
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10
Q

Describe the structure and function of the Golgi apparatus.

A

Planar stack of membrane-bound, flattened sacs cis face aligns with rER.
Molecules are processed in cisternae vesicles bud off trans face via exocytosis.
- modifies & packages proteins for export
- synthesises glycoproteins

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11
Q

Describe the structure and function of a lysosome.

A

Sac surrounded by single membrane embedded H+ pump maintains acidic conditions; contains digestive hydrolase enzymes glycoprotein coat protects cell interior:
- digests contents of phagosome
- exocytosis of digestive enzymes

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12
Q

Describe the structure and function of a ribosome.

A

Formed of protein & rRNA; free in the cytoplasm or attached to the ER.
- site of protein synthesis via translation: large subunit joints amino acids, small subunit contains mRNA binding site.

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13
Q

Describe the structure and function of the endoplasmic reticulum (ER).

A

Cisternae: network of tubules & flattened sacs extend from cell membrane through cytoplasm & connect to nuclear envelope:
- Rough ER: many ribosomes attached for protein synthesis & transport
- Smooth ER: lipid synthesis

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14
Q

Describe the structure of the cell wall.

A
  • Bacteria: made of polysaccharide murein.
  • Plants: made off cellulose microfibrils. Plasmodesmata allow molecules to pass between cells, middle lamella acts as a boundary between adjacent cell walls.
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15
Q

State the functions of the cell wall.

A
  • Mechanical strength and support.
  • Physical barrier against pathogens.
  • Part of apoplast pathway (plants) to enable easy diffusion of water.
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16
Q

Describe the structure and function of the cell vacuole in plants.

A

Surrounded by single membrane: tonoplast contains cell sap: mineral ions, water, enzymes, soluble pigments.
- controls turgor pressure
- absorbs and hydrolyses potentially harmful substances to detoxify cytoplasm

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17
Q

Explain some common cell adaptations.

A
  • Folded membrane or microvilli increase surface area e.g., for diffusion.
  • Many mitochondria = large amounts of ATP for active transport.
  • Walls one cell thick to reduce distance of diffusion pathway.
18
Q

State the role of plasmids in prokaryotes.

A
  • Small ring of DNA that carries non-essential genes.
  • Can be exchanged between bacterial cells via conjugation.
19
Q

State the role of flagella in prokaryotes.

A

Rotating tail propels (usually unicellular).

20
Q

State the role of the capsule in prokaryotes.

A

Polysaccharide layer:
- prevent desiccation
- acts as food reserve
- provides mechanical protection against phagocytosis & external chemicals
- sticks cells together

21
Q

Compare eukaryotic and prokaryotic cells.

A

Both have:
- cell membrane
- cytoplasm
- ribosomes

22
Q

Contrast eukaryotic and prokaryotic cells.

A

Prokaryotic:
- small cells & always unicellular
- no membrane-bound organelle & no nucleus
- circular DNA not associated with proteins
- 70s small ribosomes
- asexual reproduction (binary fission)
- cellulose cell wall / chitin
- capsule, sometimes plasmids & cytoskeleton
Eukaryotic:
- larger cells & often multicellular
- always have organelles & nucleus
- linear chromosomes associated with histones
- 80s larger ribosomes
- mitosis & meiosis (sexual and asexual)
- murein cell walls
- no capsule, plasmids & always cytoskeleton

23
Q

Why are viruses referred to as ‘particles’ instead of cells?

A

Acellular & non-living: no cytoplasm, cannot self-produce, no metabolism.

24
Q

Describe the structure of a viral particle.

A
  • Linear genetic material (DNA / RNA) & viral enzymes e.g., reverse transcriptase.
  • Surrounded by capsid (protein coat made of capsomeres).
  • No cytoplasm.
25
Q

Describe the structure of an enveloped virus.

A
  • Simple virus surrounded by matrix protein.
  • Matrix protein surrounded by envelop derived from cell membrane of host cell.
  • Attachment proteins on surface.
26
Q

State the role of the capsid on viral particles.

A
  • Protect nucleic acid from degeneration by restriction endonucleases.
  • Surface sites enable viral particle to bind & enter host cells or inject their genetic material.
27
Q

State the role of attachment proteins on viral particles.

A

Enable viral particle to bind to complementary sites of host cell: entry via endosymbiosis

28
Q

Describe how optical microscopes work.

A
  1. Lenses focus rays of light and magnify the view of a thin slice of specimen.
  2. Different structures absorb different amounts and wavelengths of light.
  3. Reflected light is transmitted to the observer via the objective lens and eyepiece.
29
Q

Outline how a student could prepare a temporary mount of tissue for an optical microscope.

A
  1. Obtain thin section of tissue e.g., using ultratome or by maceration.
  2. Place plant tissue in a drop of water.
  3. Stain tissue on a slide to make structures visible.
  4. Add coverslip using mounted needle at 45 degrees to avoid trapping air bubbles.
30
Q

Suggest the advantages and limitations of using an optical microscope.

A

+ colour change
+ can show living structures
+ affordable apparatus
- 2D image
- lower resolution than electron microscopes = cannot see ultrastructure

31
Q

Describe how a transmission electron microscope works.

A
  1. Pass a high energy beam of electrons through a thin slice of specimen.
  2. More dense structures appear darker since they absorb more electrons.
  3. Focus image onto fluorescent screen or photographic plate using magnetic lens.
32
Q

Suggest the advantages and limitations of using a TEM.

A

+ electrons have shorter wavelength than light = high resolution, so ultrastructure visible
+ high magnification (x500000)
- 2D imagine
- requires a vacuum = cannot show living structures
- extensive preparation may introduce artefacts
- no colour image

33
Q

Describe how a scanning electron microscope works.

A
  1. Focus a beam of electrons onto a specimen’s surface using electromagnetic lenses.
  2. Reflected electrons hit a collecting device and are amplified to produce an image on a photographic plate.
34
Q

Suggest the advantages and limitations of using a SEM.

A

+ 3D image
+ electrons have shorter wavelength than light = high resolution
- requires a vacuum = cannot show living structures
- no colour image
- only shows outer surface

35
Q

Describe magnification and resolution.

A
  • Magnification: factor by which the image is larger than the actual specimen.
  • Resolution: smallest separation distance at which 2 separate structures can be distinguished from one another.
36
Q

Explain how to use an eyepiece graticule and stage micrometre to measure the size of a structure.

A
  1. Place micrometre on stage to calibrate eyepiece graticule.
  2. Line up scales on graticule and micrometre. Count how many graticule divisions are in 100um on the micrometre.
  3. Length of 1 eyepiece division - 100um / number of divisions.
  4. Use calibrated values to calculate actual length of structures.
37
Q

State the equation to calculate the actual size of a structure from microscopy.

A

Actual size = image size / magnification
I = A x M
M = I / A
A = I / M

38
Q

Outline what happens during a cell fractionation and ultracentrifugation.

A
  1. Mince and homogenize tissue to break open cells & release organelle.
  2. Filter homogenate to remove debris.
  3. Perform differential centrifugation:
    a) spin homogenate in centrifuge
    b) the densest organelles in the mixture form a pellet
    c) filter off the supernatant and spin again at a higher speed
39
Q

State the order of sedimentation of organelle during differential centrifugation.

A

Most dense –> least dense
nucleus –> mitochondria –> lysosomes –> RER –> plasma membrane –> SER –> ribosomes

40
Q

Explain why fractionated cells are kept in a cold, buffered, isotonic solution.

A
  • Cold: slow action of hydrolase enzymes.
  • Buffered: maintain constant pH.
  • Isotonic: prevent osmotic lysis / shrinking of organelle.

Biology (20 decks)

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