Cell structure (3) Flashcards
1
Q
Describe the structure of a eukaryotic cell.
A
DNA contained within a nucleus, contains membrane-bound specialised organelles
2
Q
Describe the structure of a prokaryotic cell.
A
DNA is ‘free’ in cytoplasm and there are no organelles
3
Q
What are 2 examples of a prokaryotic cell?
A
Bacteria
Archaea
4
Q
What is the hierarchy of cell type?
A
specialised cells
tissues that perform specific function
organs made of several tissue types
organ systems
5
Q
What is the structure of cell-surface membranes?
A
fluid mosaic phospholipid bilayer with extrinsic and intrinsic proteins embedded
6
Q
What are the 3 functions of cell-surface membranes?
A
1) isolates cytoplasm from extracellular environment
2) selectively permeable to regulate transport of substances
3) involved in cell signalling/cell recognition
7
Q
What are 3 things that cell-surface membranes contain?
A
cholesterol
glycoproteins
glycolipids
8
Q
What is the role of cholesterol?
A
steroid molecule connects phospholipids and reduces fluidity
9
Q
What is the role of glycoproteins?
A
cell signalling, cell recognition and binding cells together
10
Q
What is the role of glycolipids?
A
cell signalling and cell recognition
11
Q
What is the structure of a nucleus?
A
- surrounded by a nuclear envelope
- nuclear pores
- dense nucleolus made of RNA and proteins
12
Q
What is the nuclear envelope?
A
semi-permeable double membrane
13
Q
What is the role of nuclear pores?
A
allow substances to enter and exit
14
Q
What is the function of the nucleus?
A
controls cellular processes
15
Q
What cellular processes does the nucleus control?
A
- gene expression which determines specialisation and site of mRNA transcription
- mitosis
- semiconservative replication
16
Q
What is the structure of the mitochondria?
A
- surrounded by a double membrane
- folded inner membrane which forms cristae
- fluid matrix which contains mitochondrial DNA, respiratory enzymes, lipids and proteins
17
Q
What is the role of cristae?
A
site of electron transport chain
18
Q
What is the function of mitochondria?
A
site of aerobic respiration to produce ATP
19
Q
What is the structure of chloroplasts?
A
- usually disc-shaped
- double membrane
- thylakoids stack to form grana
- intergranal lamellae attach thylakoids in adjacent grana
- stroma
20
Q
What are thylakoids?
A
flattened discs
21
Q
What are intergranal lamallae?
A
tubular extensions
22
Q
What is the stroma?
A
fluid-filled matrix
23
Q
What is the function of the chloroplast?
A
site of photosynthesis to convert solar energy to chemical energy
24
Q
What is the structure of the Golgi apparatus?
A
stack of membrane-bound, flattened sacs
25
What is the function of the Golgi apparatus?
- modifies and packages proteins for export
- synthesises glycoproteins
26
What is the structure of the lysosome?
- sac surrounded by single membrane
- embedded H+ pump maintains acidic conditions
- contains digestive hydrolase enzymes
- glycoprotein coat protects cell interior
27
What are the 2 functions of the lysosome?
- digests contents of phagosome
- exocytosis of digestive enzymes
28
What is the structure of the ribosome?
- made up of proteins and RNA
- free in cytoplasm or attached to endoplasmic reticulum
29
What don't ribosomes classify as and why?
they don't classify as organelles as they are not membrane-bound
30
What does the endoplasmic reticulum contain?
cisternae
31
What are cisternae?
network of tubules and flattened sacs
32
Where is the ER found?
extends from cell membrane, through cytoplasm, and connects to the nuclear envelope
33
What is the function of the rough ER?
many ribosomes attached for protein synthesis and transport
34
What is the function of the smooth ER?
lipid synthesis
35
What is the cell wall of bacteria made of?
polysaccharide murein
36
What is the cell wall of fungi made of?
chitin
37
What is the cell wall of plants made of?
cellulose microfibrils
38
What is the structure of the cell wall in plants?
- plasmodesmata which allows molecules to pass between cells
- middle lamella which acts as a boundary between adjacent cell walls
39
What is the function of cell wall?
- mechanical strength and support
- physical barrier against pathogens
- part of apoplast pathway in plants, to enable easy osmosis
40
What is the structure of the vacuole?
- surrounded by single membrane called tonoplast
- contains cell sap
41
What does cell sap contain?
mineral ions
water
enzymes
soluble pigments
42
What is the function of the vacuole?
- controls turgor pressure
- absorbs and hydrolyses potentially harmful substances to detoxify cytoplasm
43
What are plasmids?
- small rings of DNA found in prokaryotic cells, which carry non-essential genes
- can be exchanged between bacterial cells via conjugation
44
What are 3 common cell adaptations?
1) folded membrane or microvilli to increase surface area e.g. for diffusion
2) many mitochondria so there are large amounts of ATP for active transport
3) walls 1 cell thick to reduce diffusion pathway distance
45
What are flagella and where are they found?
rotating tail, found on prokaryotes, which propel organisms that are usually unicellular
46
What 3 structures are only found in prokaryotes?
plasmids
flagella
capsule
47
What is the structure of a capsule?
polysaccharide layer
48
What does the polysaccharide layer of a capsule do?
(What is the function of the capsule?)
- prevents loss of water
- provides mechanical protection against phagocytosis and external chemicals
- acts as a food reserve
- sticks cells together
49
What are 4 structure specific differences between prokaryotic and eukaryotic cells?
1) pro - no membrane bound organelles, euk - always have organelles
2) pro - no nucleus, euk - nucleus
3) pro - small ribosomes (70S), euk - larger ribosomes (80S)
4) pro - capsule, sometimes plasmids, cytoskeleton, euk - no capsule, no plasmids, always cytoskeleton
50
What are 3 general differences between prokaryotes and eukaryotes?
1) pro - small cells, always unicellular, euk - larger cells, often multicellular
2) pro - circular DNA not associated with proteins, euk - linear chromosomes associated with histones
3) pro - binary fission, always asexual reproduction , euk - mitosis & meiosis, sexual and/or asexual reproduction
51
What are viruses often referred to as and why?
'particles' instead of cells because they are acellular and non-living
52
Why are viruses classes as non-living?
they have no cytoplasm, cannot self-reproduce and have no metabolism
53
What is the structure of a viral particle?
- linear genetic material (DNA/RNA) with viral enzymes
- surrounded by capsid
- no cytoplasm
54
What is an example of a viral enzyme?
reverse transcriptase
55
What is a capsid?
protein coat made of capsomeres
56
What is the structure of an enveloped virus?
- simple virus surrounded by matrix protein
- matrix protein surrounded by envelope, derived from cell membrane of host cell
- attachment proteins on surface
57
What is the function of the capsid on viral particles?
- protect nucleic acid from degradation by restricting endonucleases
- surface sites enable viral particle to bind to and enter host cells or inject their genetic material
58
What is the role of attachment proteins on viral particles?
enable viral particle to bind to complementary sites on host cell and enter via endosymbiosis
59
What are the 3 steps on how optical microscopes work?
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
60
What are the 4 steps on how to prepare a temporary mount of tissue for an optical microscope?
1) obtain thin section of tissue
2) place 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
61
What are 3 advantages of an optical microscope?
+ colour image
+ can show living structures
+ affordable apparatus
62
What are 2 disadvantages of an optical microscope?
- 2D image
- lower resolution than electron microscope so cannot see ultrastructure
63
What are the 3 steps on how transmission electron microscopes work?
1) pass high energy beam of electrons through thin slice of specimen
2) denser structures appear darker since they absorb more electrons
3) focus image onto photographic plate using magnetic lenses
64
What are 2 advantages of a TEM?
+ electrons have shorter wavelength than light so the resolution is high and ultrastructure is visible
+ high magnification of x500,000
65
What are 4 disadvantages of TEM?
- 2D image
- image not in colour
- requires a vacuum so cannot show living structures
- extensive preparation may introduce artefacts
66
What is the equation for magnification?
image size
____________
actual size
67
What is the order of cell structures from most dense to least dense?
MOST
nucleus
mitochondria
lysosomes
RER
plasma membrane
SER
ribosomes
LEAST
68
What are the 2 steps on how scanning electron microscopes work?
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
69
What are 2 advantages of SEM?
+ 3D image
+ electrons have shorter wavelength than light so the resolution is high and ultrastructure is visible
70
What are 2 disadvantages of SEM?
- requires a vacuum so cannot show living structures
- image not in colour
71
What is meant by magnification?
factor by which the image is larger than the actual specimen
72
What is meant by resolution?
smallest separation distance at which 2 separate structures can be distinguished from one another
73
What are the 4 stages on how to use an eyepiece graticule?
1) place micrometer on stage to calibrate eyepiece graticule
2) line up scales on graticule and micrometer
3) count how many graticule divisions are in 100um on the micrometer
4) use calibrated valves to calculate actual length of structures
74
What is the equation to workout the length of 1 eyepiece division?
100um (micrometer)
__________________
number of divisions
75
What are the 3 steps of cell fractionation?
1) mince and homogenize tissue to break open cells and release organelles
2) filter homogenate to remove debris
3) perform ultracentrifugation
76
What are the 3 steps of ultracentrifugation?
1) spin homogenate in centrifuge
2) most dense organelles in mixture form a pellet at the bottom
3) filter off the supernatant and spin at increasingly faster speeds
77
What are the 3 features of the solution fractionated cells must be kept in?
cold, buffered, isotonic
78
Why must the solution fractionated cells are kept in be cold?
to slow action of hydrolase enzymes
79
Why must the solution fractionated cells are kept in be buffered?
to maintain a constant pH
80
Why must the solution fractionated cells are kept in be isotonic?
to prevent osmotic lysis/shrinking or organelles
