2.1 Cell Structure Flashcards
(113 cards)
1
Q
Define the term: eukaryotic cell
A
DNA is contained in a nucleus, contains membrane-bound specialised organelles.
2
Q
Define the term: prokaryotic cell
A
DNA is ‘free’ in cytoplasm, no organelles e.g. bacteria & archaea.
3
Q
State the relationship between a system and specialised cells.
A
Specialised cells → tissues that perform specific function → organs made of several tissue types → organ systems.
4
Q
What is the structure of a cell-surface membrane?
A
‘Fluid mosaic’ phospholipid bilayer with extrinsic & intrinsic proteins embedded.
5
Q
What is the function of a cell-surface membrane?
A
Isolates cytoplasm from the extracellular environment.
6
Q
What property of the cell-surface membrane allows it to regulate transport of substances?
A
It is selectively permeable.
7
Q
What role does the cell-surface membrane play in cell signaling?
A
It is involved in cell signaling and cell recognition.
8
Q
Explain the role of cholesterol in the cell-surface membrane.
A
Steroid molecule connects phospholipids & reduces fluidity.
9
Q
Explain the role of glycoproteins in the cell-surface membrane.
A
Cell signalling, cell recognition (antigens) & binding cells together.
10
Q
Explain the role of glycolipids in the cell-surface membrane.
A
Cell signalling & cell recognition.
11
Q
What surrounds the nucleus?
A
Nuclear envelope, a semi-permeable double membrane.
12
Q
What do nuclear pores do?
A
Allow substances to enter and exit the nucleus.
13
Q
What is the nucleolus made of?
A
RNA and proteins.
14
Q
What is the function of the nucleolus?
A
Assembles ribosomes.
15
Q
Nucleus function
A
Contains DNA coiled around chromatin into chromosomes. Controls cellular processes: gene expression determines specialisation & site of mRNA transcription, mitosis, semiconservative replication.
16
Q
What type of membrane surrounds a mitochondrion?
A
Double membrane
17
Q
What are the folds of the inner membrane of a mitochondrion called?
A
Cristae
18
Q
What is the site of the electron transport chain in mitochondria?
A
Cristae
19
Q
What does the fluid matrix of a mitochondrion contain?
A
Mitochondrial DNA, respiratory enzymes, lipids, proteins
20
Q
What is the structure of a chloroplast?
A
Vesicular plastid with double membrane.
21
Q
What are thylakoids in chloroplasts?
A
Flattened discs that stack to form grana and contain photosystems with chlorophyll.
22
Q
What are intergranal lamellae?
A
Tubes that attach thylakoids in adjacent grana.
23
Q
What is the stroma in chloroplasts?
A
The fluid-filled matrix.
24
Q
Mitochondria function
A
Site of aerobic respiration to produce ATP.
25
Chloroplasts function
Site of photosynthesis to convert solar energy to chemical energy.
26
What is the structure of the Golgi apparatus?
Planar stack of membrane-bound, flattened sacs.
27
Which face of the Golgi apparatus aligns with the rough endoplasmic reticulum (rER)?
The cis face.
28
Where are molecules processed in the Golgi apparatus?
In the cisternae.
29
How do vesicles bud off from the Golgi apparatus?
Via exocytosis from the trans face.
30
Golgi apparatus function
Modifies & packages proteins for export, synthesises glycoproteins.
31
What is the structure of a lysosome?
A sac surrounded by a single membrane.
32
What type of pump is embedded in the lysosome membrane?
H+ pump.
33
What conditions do lysosomes maintain?
Acidic conditions.
34
What type of enzymes do lysosomes contain?
Digestive hydrolase enzymes.
35
What protects the interior of the lysosome?
A glycoprotein coat.
36
Lysosome function
Digests contents of phagosome, exocytosis of digestive enzymes.
37
Ribosome structure
Formed of protein & rRNA free in cytoplasm or attached to ER.
38
Ribosome function
Site of protein synthesis via translation: large subunit joins amino acids, small subunit contains mRNA binding site.
39
Endoplasmic reticulum (ER) structure
Cisternae: network of tubules & flattened sacs extends from cell membrane through cytoplasm & connects to nuclear envelope.
40
Rough ER function
Many ribosomes attached for protein synthesis & transport.
41
Smooth ER function
Lipid synthesis.
42
Describe the structure of the cell wall in bacteria
Made of the polysaccharide murein.
43
Describe the structure of the cell wall in plants
Made of cellulose microfibrils, plasmodesmata allow molecules to pass between cells, middle lamella acts as boundary between adjacent cell walls.
44
Cell wall functions
Mechanical strength and support. Physical barrier against pathogens. Part of apoplast pathway (plants) to enable easy diffusion of water.
45
Cell vacuole structure in plants
Surrounded by single membrane: tonoplast contains cell sap: mineral ions, water, enzymes, soluble pigments.
46
Cell vacuole function in plants
Controls turgor pressure. Absorbs and hydrolyses potentially harmful substances to detoxify cytoplasm.
47
What is the purpose of folded membranes or microvilli in cells?
To increase surface area for diffusion.
48
What does a high number of mitochondria in a cell indicate?
Large amounts of ATP for active transport.
49
Why are some cell walls one cell thick?
To reduce the distance of the diffusion pathway.
50
Role of plasmids in prokaryotes
Small ring of DNA that carries non-essential genes. Can be exchanged between bacterial cells via conjugation.
51
Role of flagella in prokaryotes
Rotating tail propels (usually unicellular) organism.
52
What is the role of the capsule in prokaryotes?
Prevents desiccation.
53
What function does the capsule serve as a food reserve in prokaryotes?
Acts as a food reserve.
54
How does the capsule provide protection to prokaryotes?
Provides mechanical protection against phagocytosis and external chemicals.
55
What is one way the capsule affects prokaryotic cells in terms of adhesion?
Sticks cells together.
56
Comparison of eukaryotic and prokaryotic cells
Both have: Cell membrane, Cytoplasm, Ribosomes (don't count as an organelle since not membrane-bound).
57
What type of cells are prokaryotic cells?
Small cells & always unicellular
58
Do prokaryotic cells have membrane-bound organelles?
No, they do not have membrane-bound organelles
59
Do prokaryotic cells have a nucleus?
No, they do not have a nucleus
60
What is the shape of DNA in prokaryotic cells?
Circular DNA not associated with proteins
61
What type of ribosomes do prokaryotic cells have?
Small ribosomes (70S)
62
How do prokaryotic cells reproduce?
Binary fission - always asexual reproduction
63
What type of cell wall do prokaryotic plant cells have?
Cellulose cell wall
64
What type of cell wall do prokaryotic fungal cells have?
Chitin cell wall
65
What is a feature that some prokaryotic cells may have?
Capsule
66
What are plasmids in prokaryotic cells?
Sometimes present small circular DNA molecules
67
Do prokaryotic cells have a cytoskeleton?
Sometimes present
68
What type of cells are larger and often multicellular?
Eukaryotic Cells
69
Do eukaryotic cells always have organelles?
Yes
70
What type of chromosomes are associated with histones in eukaryotic cells?
Linear chromosomes
71
What is the size of ribosomes in eukaryotic cells?
80S
72
What types of cell division do eukaryotic cells undergo?
Mitosis and meiosis
73
What type of cell walls do eukaryotic cells have?
Murein cell walls
74
Do eukaryotic cells have a capsule?
No
75
Do eukaryotic cells contain plasmids?
No
76
What structural feature is always present in eukaryotic cells?
Cytoskeleton
77
Why are viruses referred to as 'particles' instead of cells?
Acellular & non-living: no cytoplasm, cannot self-reproduce, no metabolism.
78
Viral Particle Structure
Linear genetic material (DNA or RNA) & viral enzymes e.g. reverse transcriptase, surrounded by capsid (protein coat made of capsomeres), no cytoplasm.
79
Enveloped Virus Structure
Simple virus surrounded by matrix protein, matrix protein surrounded by envelope derived from cell membrane of host cell, attachment proteins on surface.
80
What is the role of the capsid in viral particles?
Protect nucleic acid from degradation by restriction endonucleases.
81
How does the capsid facilitate viral infection?
It has surface sites that enable viral particles to bind to and enter host cells or inject their genetic material.
82
Attachment proteins role on viral particles.
Enable viral particle to bind to complementary sites on host cell: entry via endosymbiosis.
83
How optical microscopes work.
Lenses focus rays of light and magnify the view of a thin slice of specimen, different structures absorb different amounts and wavelengths of light, reflected light is transmitted to the observer via the objective lens and eyepiece.
84
How to prepare a temporary mount.
Obtain thin section of tissue e.g. using ultratome or by maceration, place plant tissue in a drop of water, stain tissue on a slide to make structures visible, add coverslip using mounted needle at 45° to avoid trapping air bubbles.
85
Optical Microscope Advantages
+ colour image, + can show living structures, + affordable apparatus.
86
Optical Microscope Limitations
- 2D image, - lower resolution than electron microscopes = cannot see ultrastructure.
87
What is the principle of a Transmission Electron Microscope (TEM)?
Pass a high energy beam of electrons through a thin slice of specimen.
88
In a Transmission Electron Microscope (TEM), how do more dense structures appear?
More dense structures appear darker since they absorb more electrons.
89
What is used to focus the image in a Transmission Electron Microscope (TEM)?
Magnetic lenses.
90
Where is the image focused in a Transmission Electron Microscope (TEM)?
Onto a fluorescent screen or photographic plate.
91
TEM Advantages
+ electrons have shorter wavelength than light = high resolution, so ultrastructure visible, + high magnification (x 500000).
92
TEM Limitations
- 2D image, - requires a vacuum = cannot show living structures, - extensive preparation may introduce artefacts, - no colour image.
93
What does a Scanning Electron Microscope (SEM) focus on a specimen's surface?
A beam of electrons
94
What type of lenses does a Scanning Electron Microscope (SEM) use?
Electromagnetic lenses
95
What happens to the reflected electrons in a Scanning Electron Microscope (SEM)?
They hit a collecting device and are amplified
96
What is produced on a photographic plate in a Scanning Electron Microscope (SEM)?
An image
97
SEM Advantages
+ 3D image, + electrons have shorter wavelength than light = high resolution.
98
SEM Limitations
- requires a vacuum = cannot show living structures, - no colour image, - only shows outer surface.
99
Define magnification
Factor by which the image is larger than the actual specimen.
100
Define resolution
Smallest separation distance at which 2 separate structures can be distinguished from one another.
101
What is the first step in calibrating the eyepiece graticule?
Place micrometer on stage to calibrate eyepiece graticule.
102
What should be aligned during the calibration of the eyepiece graticule?
Line up scales on the graticule and micrometer.
103
How do you determine the number of graticule divisions in 100μm?
Count how many graticule divisions are in 100μm on the micrometer.
104
How do you calculate the length of one eyepiece division?
Length of 1 eyepiece division = 100μm / number of divisions.
105
What is the purpose of using calibrated values in microscopy?
To calculate the actual length of structures.
106
Actual Size Calculation
actual size = image size / magnification.
107
What is the first step in the cell fractionation process?
Split and homogenize tissue to break open cells and release organelles.
108
What is done to the homogenate in the cell fractionation process?
Filter homogenate to remove debris.
109
What is differential centrifugation?
A process that involves spinning the homogenate in a centrifuge to separate organelles based on density.
110
What happens to the most dense organelles during centrifugation?
They form a pellet at the bottom of the centrifuge tube.
111
What is done after the first spin in differential centrifugation?
Filter off the supernatant and spin again at a higher speed.
112
Order of Sedimentation
Most dense → least dense: nucleus → mitochondria → lysosomes → RER → plasma membrane → SER → ribosomes.
113
Why are fractionated cells kept in a cold, buffered, isotonic solution?
Cold: slow action of hydrolase enzymes, buffered: maintain constant pH, isotonic: prevent osmotic lysis/ shrinking of organelles.
