B3 Cell Structure Flashcards
(128 cards)
1
Q
Function of nucleus
A
Site of DNA replication and transcription (making mRNA)
Contains genetic code for each cell
2
Q
Structure of nucleus
A
Nuclear Envelope- double membrane
Nuclear Pores
Nucleoplasm - granular, jelly-like material
Chromosomes -protein-bound, linear
DNA
Nucleolus - smaller sphere inside which is the site of RNA production and makes ribosomes.
3
Q
Function of endoplasmic reticulum
A
RER - Protein Synthesis
SER - Synthesis and store lipids and carbohydrates
4
Q
Structure of endoplasmic reticulum
A
Rough and smooth ER have folded membranes called cisternae
Rough have ribosomes on cisternae
5
Q
Function of Golgi apparatus and vesicles
A
Add carbohydrates to proteins to form glycoproteins
• Produce secretory enzymes
Secrete carbohydrates
Transport, modify and store lipids
• Form lysosomes
Molecules are ‘labelled’ with their destination
Finished products are transported to cell surface in Golgi vesicles where they fuse with the membrane and the contents in released.
6
Q
Structure of Golgi apparatus and vesicles
A
Folded membranes making cisternae
Secretary vesicles pinch off from the cisternae
7
Q
Function of lysosomes
A
Hydrolyse phagocytic cells
• Completely break down dead cells (autolysis)
• Exocytosis - release enzymes to outside of cell to destroy material
• Digest worn out organelles for reuse of materials
8
Q
Structure of lysosomes
A
Bags of digestive enzymes - can contain 50 different enzymes.
9
Q
Structure of mitochondria
A
Double membrane
Inner membrane called the cristae
Fluid centre called the mitochondrial matrix
Loop of mitochondria DNA
10
Q
Function of mitochondria
A
• Site of aerobic respiration
Site of ATP production
• DNA to code for enzymes needed in respiration
11
Q
Structure of ribosomes
A
Small, made up of two sub-units of protein and rRNA
80s- large ribosome found it eukaryotic cells (25nm)
70S - smaller ribosome found in prokaryotic cells, mitochondria and chloroplasts.
12
Q
Function of ribosomes
A
Site of protein synthesis
13
Q
Structure of vacuole
A
Filled with fluid surrounded by a single membrane called a tonoplast
14
Q
Function of vacuole
A
Make cells turgid and therefore provide support
• Temporary store of sugars and amino acids
• The pigments may colour petals to attract pollinators.
15
Q
Function of chloroplasts
A
Site of photosynthesis
16
Q
Structure of chloroplasts
A
Surrounded by a double membrane
Contains thylakoids (folded membranes embedded with pigment)
Fluid filled stroma contains enzymes for photosynthesis
Found in plants
17
Q
Function of cell wall
A
Provide structural strength to cell
18
Q
Structure of cell wall
A
In plant and fungi cells
Plants- made of microfibrils of the cellulose polymer.
Fungi - made of chitin, a nitrogen-containing polysaccharide
19
Q
Function of plasma membrane
A
Controls entrance and exit of molecules
20
Q
Structure of plasma membrane
A
Found in all cells
Phospholipid bilayer - molecules embed within and attached on the outside (proteins, carbohydrates, cholesterol)
21
Q
Calc mitotic index
A
Count how many cells are visible in filed of view and number of cells visible that are in stage of mitosis
Mitotic index = (number of cells in mitosis / total number of cells) x 100
22
Q
What are the 4 stages of mitosis
A
Prophase
Metaphase
Anaphase
Telophase
23
Q
Info about mitosis
A
1 round of division
Genetically identical cells are made
Diploid cells are made
Growth and repair
24
Q
What happens in prophase
A
Chromosomes condense + become visible
Centrioles separate + move to opp ends of poles of cell
Nucleolus disappears
25
What happens in anaphase
Spindle fibres start to retract + pull centromere and chromatids they’re bound to towards opp poles
Centromere divide in 2
Individual chromatids are pulled to each opp pole (chromatids now referred to as chromosomes)
Requires energy in form of atp - provided by respiration in mitochondria
26
What happens in metaphase
Chromosomes align along equator
Spindle fibres released from poles now attach to centromere and chromatid
27
What happens in telophase
Chromosomes at each pole become longer + thinner again
Spindle fibres disintegrate, nucleus starts to reform
Nuclear membrane reforms
Nucleoli reappear
Cytoplasm splits in 2 to create 2 new genetically identical cells
28
What are the 3 stages of cell cycle
Interphase (G1, S, G2)
Nucelar division (mitosis + meiosis)
Cytokinesis
29
What is interphase
Longest stage in cell cycle
When organelles double, cell grows and DNA replicates
30
How do prokaryotic cells replicate
Binary fission and viruses don’t undergo cell division as they’re non-living
Viruses replicate inside of host cells they invade by injecting their nuclei acid into cell to replicate virus particles.
31
What are 3 types of microscopes
Optical (light) microscopes
Transmission electron microscopes
Scanning electron microscopes
32
Define magnification
how many times larger the image is compared to the object.
33
Define resolution
the minimum distant between two objects in which they can still be viewed as separate.
34
Optical (light) microscope
Light Beam condensed to create image
Poor resolution - light have longer wavelength
Low magnification
Coloured images
Can view living samples
35
Electron microscope (scanning or transmission)
Electron beam condensed to create image
Electromagnets used to condense beam
High resolution - electrons have short wavelength
High magnification
Black and white images
Sample must be in vacuum + non-living
36
Are small organelles visible in light microscope
No because of poor resolution of microscope - long wavelength of light
37
Why must Samples be in vacuum in Electron microscope
As Electrons are absorbed by air
38
Why must Samples be stained in Electron microscope
The image is in black and white
39
How is an image produced in TEM
Extremely thin specimen stained and place in vacuum
Electron gun produces electron beam that passes through specimen
Some parts absorb electrons and appear dark
Image produced is 2d - shows detailed images on internal structure of cells
40
How is an image produced in SEM
The specimens do not need to be thin, as the electrons are not transmitting through.
Instead, electrons beamed onto surface and electrons are scattered in diff ways depending on contours.
This produces a 3D image.
41
Magnification equation
Magnification = image size / actual size
42
Converting units
M - mm - micrometre - nm
——> x1000
<—— divide by 1000
43
What is cell fractionation used for
To isolate diff organelles so they can be studied
This enable individual organelle structures and functions to be studied
44
What happens in cell fractionation 1st
Cells are broken open to release contents and organelles are then separated
45
Why must cells be prepared in cold, isotonic, and buffered solution
Cold:
To reduce enzyme activity. When cell is broken open enzymes are released which could damage organelles
Isotonic:
organelles must be same water potential as solution to prevent osmosis, as this could cause organelles to shrivel / burst.
Buffered:
solution has pH buffer to prevent damage to organelles
46
What are the 2 main steps in cell fractionation
Step 1 = homogenisation
Step 2 = ultracentrifugation
47
What happens in step 1 of cell fractionation
cells must be broken open (homogenised) and this is done using blender.
cells are blended in cold, isotonic and buffered solution.
48
What happens in step 2 of cell fractionation
filtered solution is spun at high speed in centrifuge.
This separates organelles according to their density.
49
The order of organelle fractionation
1st : (slowest speed 1st)
Nuclei
Chloroplasts
Mitochondria
Lysosomes
Endoplasmic reticulum
Ribosomes
Last:(fastest speed)
50
How does the centrifuge separate the pellets
centrifuge spins at high speeds and centrifugal forces causes pellets of most dense organelle to form at bottom of tube.
process repeated at increasingly faster speeds, removing supernatant each time (liquid) leaving behind pellet ( isolated organelle).
supernatant is then spun again in centrifuge and process is repeated.
51
Suggest and explain the function of enzyme ATP hydrolase in absorbing amino acids.
1.Hydrolysing ATP into ADP + Pi releases energy
2. This energy actively transports sodium ions out of the epithelial cells into the blood
3. This creates a sodium ion concentration gradient from the ileum into the epithelial cells
4. Sodium ions are cotransported into the epithelial cells with amino acids
52
(Mitosis practical) explain why the student used the 1st 5mm from onion root tip
This is where mitosis occurs
53
(Mitosis practical) explain why the student pressed down on the cover slip firmly
To create a single layer of cells so that light can pass through the specimen
54
(Mitosis practical) explain why the student added acid to the root
To break down links between cells/cell walls
55
Describe how HIV replicates inside of helper T cells.
1. RNA is converted into DNA using the enzyme reverse transcriptase
2. The DNA is inserted into the DNA of the helper T cell
3. The DNA is transcribed into mRNA
4. This HIV mRNA is then translated into HIV proteins to make a new viral particles
56
Function of the flagella in prokaryotic cell
Flagella rotates to enable bacteria to move
57
What is the capsule made of and its function
A slimy layer made of protein
This prevents the bacteria from desiccating (drying out) and protects the bacteria against the host's immune system.
58
What are plasmids
small loops of DNA which only carry a few genes.
59
What is the cell wall like in prokaryotic cell
Contains murein (a glycoprotein)
60
What is the cell wall like in eukaryotic cell
In plant and fungi cells
Plants- made of microfibrils of the cellulose polymer.
Fungi - made of chitin, a nitrogen-containing polysaccharide
61
Structure of nucleus in prokaryotic cell
No nucleus - Instead of a nucleus there is a single circular DNA molecule free in the cytoplasm which is not protein bound.
62
What don’t prokaryotic cells contain
Membrane bound organelles
E.g. mitochondria, chloroplasts, endoplasmic reticulum, Golgi, nucleus
63
What are the Key differences between prokaryotic cells and eukaryotic cells and what might prokaryotic cells also contain
The cells are much smaller.
No membrane bound-organelles
Smaller ribosomes
No nucleus
A cell wall made of murein
They may also contain:
Plasmids
A capsule around the cell
Flagella
64
State what cell cycle is and outline its stages
Cycle of division with intermediate growth periods
1. Interphase
2. Mitosis or meiosis (nuclear division)
3. Cytokinesis (cytoplasmic division)
65
Explain why cell cycles doesn’t occur in some cells
After differentiation, some types of cell in multicellular organisms (e.g. neurons) no longer have ability to divide
66
What is difference between cell cycle and mitosis
Cell cycle includes growth periods between divisions
Mitosis is only 10% of cycle and refers only to nuclear division
67
Outline what happens during interphase
G1: cell synthesises for replication e.g. tubulin for spindle fibres and cell size doubles
S: DNA replicates. Chromosomes consist of 2 sister chromatids joined at a centromere
G2: organelles divide
68
State purpose of mitosis
Produces 2 genetically identical daughter cells for:
- growth
- cell replacement/tissue repair
- asexual reproduction
69
Name stages of mitosis
PMAT
1. Prophase
2. Metaphase
3. Anaphase
4. Telophase
70
Outline what happens during prophase
1. Chromosomes condense, becoming visible.
(X-shaped: 2 sister chromatids joined at centromere)
2. Centrioles move to opp poles of cell (animal cells) & mitotic spindle fibres form
3. Nuclear envelope & nucleolus break down = chromosomes free in cytoplasm
71
Outline what happens during metaphase
Sister chromatids line up at cell equator, attached to mitotic spindle by their centromeres
72
Outline what happens during anaphase
Requires energy from ATP hydrolysis
1. Spindle fibres contract = centromeres divide
2. Sister chromatids separate into 2 distinct chromosomes & are pulled to opp poles of cell (looks like ‘V’ shapes facing each other)
3. Spindle fibres break down
73
Outline what happens during telophase
1. Chromosomes decondense, becoming invisible again
2. New nuclear envelopes form around each set of chromosomes = 2 new nuclei, each with 1 copy of each chromosome
74
Explain procedure for a root tip squash experiment
1. Prepare a temporary mount of root tissue
2. Focus an optical microscope on the slide.
Count total number of cells in field of view and number of cells in a stage of mitosis
3. Calculate mitotic index (proportion of cells undergoing mitosis)
75
Outline how to prepare a temporary mount of root tissue
1. Place root in HCl to halt cell division & hydrolyse middle lamella
2. Stain root tip with a dye that binds to chromosomes
3. Macerate tissue in water using mounted needle
4. Use mounted needle 45* to press down coverslip & obtain a single layer of cells. Avoid trapping air bubbles
76
Name 2 dyes that bind to chromosomes
Toluidine blue (blue)
Acetic ore in (purple-red)
77
Why’s only root tip used when calculating a mitotic index
Meritstematic cells at root tip are actively undergoing mitosis
Cells further from root tip are elongating rather than dividing
78
What are tumour suppressor genes and proro-oncogenes
Genes that code for proteins to trigger apoptosis (programmed death of damaged cells) / slow cell cycle (e.g. p53 acts between G1 & S in interphase so damaged DNA cannot replicate)
79
What are proto-oncogenes
Genes that code for proteins to stimulate cell cycle to progress from 1 stage to next
80
How can mutation to tumour suppressor genes & proto-oncogenes casue cancer
Tumour suppressor: no production of a protein needed to slow cell cycle
Proto-oncogenes: form permanently-activated oncogenes
Disruption to cell cycle —> uncontrolled cell division —> tumour
81
Suggest how cancer treatments control rate of cell division
Disrupt cell cycle:
- prevent DNA replication
- disrupt spindle formation = inhibit metaphase/anaphase
NB: can also damage healthy cells
82
How do prokaryotic cells replicate
Binary fission:
1. DNA loop replicates. Both copies stay attached to cell membrane. Plasmids replicate in cytoplasm.
2. Cell elongates, separating the 2 DNA loops
3. Cell membrane contracts & septum forms
4. Cell splits into 2 identical progeny cells, each with 1 copy of the DNA loops but a variable number of plasmids
83
Estimate the exponential growth of bacteria within 8 hours. Assume binary fission occurs once every 20 minutes & there is 1 bacterium at the start
8 X 60 = 480 minutes
480 / 20 = 24 divisions
2^24
84
Why are viruses classified as non-living
They are acellular:
No cytoplasm, no metabolism & cannot self-replicate
85
Outline how viruses replicate
1. Attachment proteins attach to receptors on host cell membrane
2. Enveloped viruses fuse with cell membrane or move in via endocytosis & release DNA/RNA into cytoplasm or viruses inject DNA/RNA
3. Host cell uses viral genetic info to synthesise new viral proteins/nucleic acid
4. Components of new viral particle assemble
86
How do new viral particles leave host cell
a) bud off & use cell membrane to form envelope
b) cause lysis of host cell
87
Why is it so difficult to develop effective treatments against viruses
Replicate inside living cells = difficult to kill them without killing host cells
88
Define eukaryotic and prokaryotic cell
Eukaryotic: DNA is contained in a nucleus, contains membrane-bound specialised organelles
Prokaryotic: DNA is ‘free’ in cytoplasm, no organelles e.g. bacteria & archaea
89
State relationship between a system and specialised cells
Specialised cells —> tissues that perform specific function —> organs made of several tissue types —> organ systems
90
Describe structure & function of cell-surface membrane
‘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
91
Explain role of cholesterol & glycoproteins & glycolipids in cell-surface membrane
Cholesterol: steroid molecule connects phospholipids & reduces fluidity
Glycoproteins: cell signalling, cell recognition (antigens) & binding cells together
Glycolipids: cell signalling & cell recognition
92
Describe structure of nucleus
Surrounded by nuclear envelope, a semi-permeable double membrane
Nuclear pores allow substances to enter/exit
Dense nucleolus made of RNA & proteins assembles ribosomes
93
Describe function of nucleus
Contains DNA coiled around chromatin into chromosomes
Controls cellular processes: gene expression determines specialisation & site of mRNA transcription, mitosis, semiconservative replication
94
Describe structure of mitochondrion
Surrounded by double membrane folded inner membrane forms Cristae: site of electron transport chain
Fluid matrix: contains mitochondrial DNA, respiratory enzymes, lipids, proteins
95
Describe structure of chloroplast
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
96
State function of mitochondria and chloroplasts
Mitochondria - site of aerobic respiration to produce ATP
Chloroplasts - site of photosynthesis to convert solar energy to chemical energy
97
Describe structure and function of Golgi apparatus
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
98
Describe structure & function of a lysosome
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
99
Describe structure & function of a ribosome
Formed of protein & rRNA free in cytoplasm or attached to ER
- site of protein synthesis via translation:
. Large subunit: joins amino acids
. Small subunit: contains mRNA binding site
100
Describe structure and function of endoplasmic reticulum (ER)
Cisternae: network of tubules & flattened sacs extends from cell membrane through cytoplasm & connects to nuclear envelope:
- RER= many ribosomes attached for protein synthesis & transport
- SER = lipid synthesis
101
Describe structure of cell wall
Bacteria =
- made of polysaccharide murein
Plants:
- made of cellulose microfibrils
- plasmodesmata allow molecules to pass between cells, middle lamella acts as boundary between adjacent cell walls
102
State functions of cell wall
Mechanical strength and support
Physical barrier against pathogens
Part of apoplast pathway (plants) to enable easy diffusion of water
103
Describe structure of cell vacuole in plants
Surrounded by single membrane: tonoplast
Contains cell sap: minerals, water, enzymes, soluble pigments
- controls turgor pressure
- absorbs and hydrolyses potentially harmful substances to detoxify cytoplasm
104
Explain some common cell adaptations
Folded membrane or microvilli increase SA e.g. for diffusion
Many mitochondria = large amounts of ATP for active transport
Walls 1 cell thick to reduce distance of diffusion pathway
105
State role of plasmids in prokaryotes
Small ring of DNA that carries non-essential genes
Can be exchange between bacterial cells via conjugation
106
State role of flagella in prokaryotes
Rotating tail propels (usually unicellular) organism
107
State role of capsule in prokaryotes
Polysaccharide layer:
- prevents desiccation
- acts as food reserve
- provides mechanical protection against phagocytosis & external chemicals
- sticks cells together
108
Compare eukaryotic and prokaryotic cells
Both have:
- cell membrane
- cytoplasm
- ribosomes (don’t count as an organelle since not membrane-bound)
109
Contrast eukaryotic & prokaryotic cells
Prokaryotic:
- small cells & always unicellular
- no membrane-bound organelles & no nucleus
- circular DNA not associated with proteins
- small ribosomes (70S)
- binary fission —> always asexual reproduction
- cellulose cell wall (plants)/chitin (fungi)
- capsule, sometimes plasmids & cytoskeleton
Eukaryotic:
- larger cells & often multicellular
- always have organelles & nucleus
- linear chromosomes associated with histones
- larger ribosomes (80S)
- mitosis & meiosis —> sexual and/or asexual
- Murein cell wallls
- no capsule, no plasmids, always cytoskeleton
110
Why are viruses referred to as ‘particles’ instead if cells
Acellular & non-living:
No cytoplasm, can’t self-reproduce, no metabolism
111
Describe structure of a viral particle
Linear genetic material (DNA or RNA) & viral enzymes e.g. reverse transcriptase
Surrounded by capsid (protein coat made by capsomeres)
No cytoplasm
112
Describe 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
113
State role of capsid on viral particles
Protect nucleic acid from degradation by restriction endonucleases
Surface sites enable viral particle to bind to & enter host cells or inject their genetic material
114
State role of attachment proteins on viral particles
Enable viral particle to bind to complementary sites on host cell: entry via endosymbiosis
115
Describe how optical microscopes work
1. Lenses focus rays of light +magnify 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 eye piece
116
Outline how a student could prepare a temporary mount of tissue for an optical microscope
1. Obtain thin section of tissues 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* to avoid trapping air bubbles
117
Suggest advantage and limitations of using an optical microscope
Pros
- Colour image
- Can show living structures
- Affordable apparatus
Cons
- 2D image
- Lower resolution than electron microscopes = cannot see ultrastructure
118
Describe how a transmission electron microscope (TEM) works
1. Pass a high energy beam of electrons through 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 lenses
119
Suggest advantages and limitations of using a TEM
Pros
- Electrons have shorter wavelength than light = high resolution, so ultrastructure visible
- high magnification (X 500,000)
Cons
- 2D image
- requires vacuum = cannot show living structures
- extensive preparation may introduce artefacts
- no colour image
120
Describe how scanning electron microscope (SEM) works
1. Focus beam of electrons onto specimens surface using electromagnetic lenses
2. Reflected electrons hit a collecting device + are amplified to produce an image on a photographic plate
121
Suggest advantages and limitations of using a SEM
Pros
- 3D image
- electrons have shorter wavelength than light = high resolution
Cons
- requires vacuum = cannot show living structures
- no colour image
- only shows outer surface
122
Define magnification
Factor by which image is larger than actual specimen
123
Define resolution
Smallest separation distance at which 2 separate structures can be distinguished from 1 another
124
Explain how to use an eyepiece graticule and stage micrometer to measure size of a structure
1. Place micrometer on stage to calibrate eyepiece graticule
2. Line up scales on graticule and micrometer. Count how many graticule divisions are in 100 micrometers on micrometer
3. Lengths of 1 piece division = 100 micrometers divided by number of divisions
4. Use calibrated values to calculate actual length of structures
125
State equation to calculate actual size of structure from microscope
Actual size = image size
——————
Magnification
126
Outline what happens during cell fractionation and ultracentrifugation
1. Mince & homogenize tissue to break open cells & release organelles
2. Filter homogenate to remove debris
3. Perform differential centrifugation:
a) spin homogenate
b) most dense organelles in mixture form a pellet
c) filter off supernatant and spin again at higher speed
127
State order of sedimentation of organelles during differential centrifugation
Most dense —> least dense
Nucleus —> mitochondria —> lysosomes —> RER —> plasma membrane —> SER —> ribosomes
128
Explain why fractionated cells are kept in a cold, buffered, isotonic solution
Cold = slow action of hydrolase enzyme
Buffered = maintain constant pH
Isotonic = prevent osmotic lysis/shrinking of organelles
