cells and membranes Flashcards
1
Q
magnification and resolution of a light microscope
A
x1500
200nm
2
Q
compare magnification and resolution of a TEM and an SEM
A
TEM: mag-x500,00
res-0.1nm
SEM:mag-x100,000
res-20nm
3
Q
define magnification
A
the degree to which the size of an image is larger than the object itself
4
Q
define resolution
A
the shortest distance between two points that can be distinguished clearly
5
Q
two ways specimen are prepared for light microscopes
A
sectioning- embedded in wax, thin sections are cut out without distorting structure
staining- chemicals bind on or in specimen. some structures take up more stain, this shows contrast
6
Q
what stains DNA dark red?
A
acetic orcein
7
Q
what stains bacterial cell walls?
A
gentian violet
8
Q
what are and explain the conditions of the solution the tissue is placed in before cell fractionation?
A
ice cold- reduces enzyme activity that might digest the organelles.
same water potential as tissue- prevents cell lysis or bursting due to osmosis
buffered- so pH does not fluctuate. any change could alter the structure of the organelles or affect functioning of enzymes by denaturing proteins
9
Q
what are the 2 steps of cell fractionation?
A
1.homogenistation
2.ultracentrifugation
10
Q
describe the steps of homogenisation
A
-cells are broken up by a homogeniser (blender)
-this breaks the plasma membranes and releases the organelles from the cell
-the resultant fluid (homogenate) is filtered to remove any complete cells or debris through a gauze
11
Q
define ultracentrifugation
A
process by which fragments in the filtered homogenate are separated in a centrifuge
rubes of homogenate are spun at very high speeds creating a centrifugal force towards the bottom of the tube
12
Q
describe the steps of ultracentrifugation
A
-tube of filtrate is placed in centrifuge, spun relatively sow speed
-nuclei most dense, travel to bottom and form a pellet
- the fluid at the top (supernatant) is removed and transferred to another tube and spun faster and longer
-mitochondria separated next
13
Q
what is the order of density of organelles?
A
nucleus
chloroplasts
mitochondria
lysosomes
rough ER
smooth ER
golgi
ribosomes
14
Q
what is needed in order for a centrifuge to work?
A
tubes must be balanced with another tube opposite
15
Q
how does an optical microscope work?
A
-visible light passes through the lens system to enable the user to see the specimen
- most cells are transparent so will need staining
-this kills the cells
16
Q
advantages of light microscopes?
A
-can include living organism (e.g. daphnia and euglena)
-easy to use and affordable
-no radiation risk
-low voltage needed
17
Q
limitations of light microscopes?
A
-cant use for ultrastructures
-cant distinguish two points closer than 200nm
-lower magnification and resolution
18
Q
why do light microscopes have a lower resolution than electron microscopes?
A
light has longer wavelengths than electrons so images have a lower resolution
19
Q
what can we use images for?
A
-to find the magnification of images
- to find actual size of image
20
Q
how do electron microscopes work?
A
uses beams of electrons which are focused by magnets
21
Q
how does a TEM work?
A
-electron beams pass through very thin section of sample
-sample is prepared by dipping in a heavy metal eg lead (this slows electrons down)
- some structures absorb more so appear dark. some allow electrons to pass, appearing brighter
-2D
-black and white
22
Q
how does an SEM work?
A
-electron beam directed on to the surface of the sample
-electrons bounce off sample and are detected by several sensors
-3D
-black and white
-image of surface detail
23
Q
what can the final image on the screen to photographed to give?
A
a photomicrograph
24
Q
what are the limitations of electron microscopes?
A
-whole system must be in a vacuum so cant be living
-complex staining process
-image may contain artefacts from the preparation and staining.
25
what are artefacts?
things that result from the way the specimen is prepared
26
what is the eyepiece graticule?
a glass disc with a scale etched on.
27
how is an eyepiece graticule calibrated for the objected lens?
line up the eyepiece graticule and stage micrometer
28
define uncertainty
amount of error your measurements may have
29
how to reduce uncertainty?
use instruments with smaller scale
30
formula for percentage error?
(uncertainty/reading)x100
31
define organelles
compartments within a cell with specific functions
32
define eukaryotic cell
-have a distinct nucleus
-have membrane bound organelles
33
differences of plant cells to animal cells
-starch grain
-chloroplasts
-cellulose cell wall
34
structure and function of the components of the nucleus:
nuclear envelope: S-double membrane with fluid between that contains nuclear pores
F- controls entry and exit of materials in and out of the nucleus
nuclear pores: S- gaps within the nuclear membrane
F- allows the passage of large molecules such as messenger RNA (3000 approx. pores)
nucleoplasm: S-jelly like material
F- makes up the bulk of the nucleus
chromosomes S- linear DNA and histone proteins
F- codes for proteins
nucleolus: S- small dense spherical region within the nucleoplasm
F- makes rRNA and ribosomes
35
structure of endoplasmic reticulum
series of flattened membrane sacs called cristae
36
structure and function of RER?
S- studded with ribosomes
-large SA
F- synthesis of proteins and glycoproteins
- pathway for the transport of protein
37
structure and function if the SER?
S- no ribosomes so appears smooth
-cisternae are tubular
F- synthesise, store, transport lipids also ions
38
what type of cells need an extensive endoplasmic reticulum?
examples?
cells that manufacture and store large quantities of carbs, proteins and lipids
e.g. liver cells and epithelial cells that line the intestines
39
structure and function of mitochondria?
Site of AEROBIC respiration
Produces ATP (releases energy)
Contains short, circular DNA (not associated with proteins)
Has a double membrane. The inner membrane is folded forming cristae.
Contains smaller (70S) ribosomes (thought to have evolved from prokaryotic cells.)
40
what type of cells need lots of mitochondria? why?
metabolically active cells like
muscle, epithelial cells
require lots of ATP
mitochondria synthesise ATP in aerobic respiration, requires oxygen
41
Golgi apparatus structure and function?
S- stack of membrane bound flattened sacs called cisternae with small, rounded, hollow structures called vesicles
Modifies proteins (e.g. by adding carbohydrate groups to form a glycoprotein or lipid groups to make a lipoprotein)
Stores proteins
Packages proteins into vesicles
Transport vesicles to cell surface
42
where is the golgi well developed?
secretory cells such as epithelial cells that line the intestines
43
chloroplast structures and functions
Chlorophyll absorb light for photosynthesis to produce carbohydrates
Has a double membrane. Inside there are thylakoid membranes which can form a stack called a granum (pl. grana). The grana are linked by lamellae.
Contain starch grains
44
lysosomes structure and function
A vesicle that contains hydrolytic enzymes (lysozymes) which are used to digest molecules
45
give an example of a lysosome
white blood cell lysosomes help to hydrolyse engulfed pathogens
46
vesicles structure and functions
S-membrane bound sacs
F-used to transport diff substances around cells.
-vesicles fuse with the cell surface membrane when substances are secreted by cell
-requires ATP for movement
47
ribosomes structure and function
S- no membrane
-two subunits one small, one large
-each contain ribosomal RNA and protein
F-site of protein synthesis
48
permanent vacuole in plants structure and function
Tonoplast – a membrane surrounding the vacuole
When the vacuole is full of fluid the cell becomes turgid.
Temporary food store containing sugars and amino acids
Contains pigments (colour petals)
49
whats the cell wall made of in plants, fungi and bacteria and functions
S-plants-cellulose
fungi-chitin
bacteria-peptidoglycan/murein
F- strong wall for support and strength
-prevent cell bursting
50
cytoskeleton structure and function
S-network of protein fibres
F-support, shape
-holds organelles in place or allows them to move through cytoplasm
-movement of chloroplasts in cell division
-changing shape of cell surface membrane during endo/exocytosis
51
what are the steps of division of labour?
1) info for protein on gene in DNA, makes copy of gene on mRNA by transcription
2) mRNA passes out nucleus via nuclear pore in envelope
3) mRNA binds to ribosome on RER, begins production of a protein-translation
4) RER packages protein into vesicle
5)vesicle fuses w/ the membrane of Golgi transporting protein into Golgi
6) Golgi modifies protein through addition of carbs
7)Golgi packages modified protein into a vesicle, transports protein towards plasma membrane
8)The vesicle fuses w/ plasma membrane ready to release outside of cell
9) protein is secreted from cell by exocytosis
52
function of flagellum?
locomotion
53
slime capsule structure and function?
S-polysaccharide outermost layer
F- prevents detection in a host body
-prevents desiccation (drying out, dehydrated)
54
what's the plasmids role in antibiotic resistance?
can be passed from one bacteria to another containing the gene
55
differences of prokaryotes and eukaryotes?
pro-no distinct nucleus, only on DNA
euk- distinct nucleus with a nuclear membrane
pro- DNA no histone proteins
pro-circular DNA in plasmids
euk- linear DNA
pro- no membrane bound organelles
euk- membrane bound orgs e.g. vesicles and lysosomes
pro-smaller 70s ribosomes
euk-larger 80s ribosomes
56
similarities between prokaryotes and eukaryotes?
both have ribosomes, cytoplasm, membrane made of phospholipids,
57
how do prokaryotes divide?
binary fission
58
what does binary fission involve?
1. replication of DNA and Plasmids followed by...
2. division of cytoplasm to produce two daughter cells, each with a single copy of the circular DNA and a variable number of copies of plasmids
59
what are the steps of binary fission?
1. circular DNA and plasmids replicate
2.cell gets bigger, DNA moves to opp poles
3.cytoplasm begins to divide, new cell wall forms
4.cytoplasm divides
two daughter cells are produced
each has one copy of circular DNA, variable number of plasmids
60
how do antibiotics work?
-one way is preventing bacteria from making normal cell walls
-inhibits enzymes required for synthesis and assembly of peptide cross linkages in cell walls
-this weakens cell wall, unable to withstand pressure
-cell bursts, bacterium dies from osmosis
61
structure and functions of Akaryote -viruses
-capsid
-middle- capsomere
-genetic material
-reverse transcriptase
-attachment proteins
-mainly nucleic acids
62
why are viruses considered not living?
-they cant replicate outside of host cells
-don't respire
63
what is a capsid?
a protein coat on a virus
64
how often is binary fission?
every 20 mins
65
what is the function of attachement proteins?
to bind to receptor protein on cell surface membrane of host cell to allow virus to insert DNA/nucleic acid to cause host cell to make new viruses
66
how do viruses replicate after being inserted?
1.viral RNA converted into viral DNA using an enzyme- reverse transcriptase
2.viral DNA is inserted into host cell DNA
3.DNA transcribed into viral mRNA
4.viral mRNA translated into new viral proteins
5.these proteins are then assembeled into viral particles
6.these viral particles ''bud off'' the cell membrane of the host cell, exit the cell and enter the surrounding fluid
67
what is the membrane made up of ?
phospholipid molecules arranged in a bilayer and proteins
68
how is the bilayer seen under an electron microscope?
two dark bands
69
why is the membrane described as fluid mosaic?
fluid=phospholipids and proteins are free to move laterally
mosaic=proteins have a scattered arrangement within the phospholipid bilayer
70
who came up with the fluid mosaic model in 1972?
singer and nicholson
71
function of phospholipids in bilayer?
-act as a barrier to water soluble,polar molecules and ions
-allow lipid soluble,small molecules and non polar substances to diffuse through
-make membrane flexible and self sealing making endo and exocytosis possible
72
cholesterol in the membrane structure and function?
S-fits between fatty acid tails, binds
F-stability and fluidity of membrane
-prevents being too fluid at high temps and solidifying at low temps
73
glycolipids structure and function in the membrane?
s-phospholipids with carbohydrate attached
F- cell signalling and recognition
-cell adhesion = helps stick cells together and to basement membranes to form tissues
74
what are the two types of channel proteins?
intrinsic
extrinsic
75
what are the two types of intrinsic proteins?
carrier
channel
76
structure and function of channel proteins in the membrane?
S-instrinsic =carrier and channel
extrinsic= span 1/2 the membrane
F-intrinsic=allow transport of hydrophylic polar molecules like glucose and ions through phospholipid bilayer.
exrinsic=cell signalling
-cell recognition
-enzymes eg mitochondria cristae for respiration
-receptors for signalling between cells eg hormone receptors
-cell adhesion
77
structure and function of glycoproteins?
S- protein with carbohydrate attached
F-receptors for signalling molecules eg hormones and neurotransmitters
-cell signalling and recognition
-cell adhesion
78
give 4 roles of membranes within cells
1.compartmenalisation
2.holding components of metabolic pathways in place. eg enzymes for aerobic respiration in mitochondria
3.control what enters or leaves the organelle
4. sites of attachment eg enzymes, ribosomes
79
give 4 roles of the membrane at the surface of cells
1.separate cell contents from outside environment
2. cell recognition and signalling
3.regulating transport of materials into or out of cells
4.create/maintain conc gradients
80
what is cell signalling?
processes that lead to communication and coordination between cells so they can work together to bring about a response
81
what does cell signalling to allow?
-comunication,coordiantion, response
- cells to be recognised as self so prevents cells from being destroyed by immune system
82
describe the process of cell signalling
protein receptors found on target cells have a specific shape complementary only to specific hormone or neurotransmitter. they will bind with the hormone to allow the cell to respond in a particular way
83
give an example of cell signalling
insulin receptor. insulin is released when there is increased blood glucose concentration
cell responds by taking up more glucose to reduce the blood glucose levels
84
what happens at 35-50 degrees to the membrane? explain trend
increase in temperature increases KE of phospholipids and protein molecules in membrane
molecules being transported have more KE and can diffuse accross the membrane more quickly
85
what happens to membrane at 50-60 degrees? explain trend
increase of temp denatures proteins making membrane more permeable
becomes more fluid
causes gaps to open temporarily in bilayer and results in molecules/ions diffusing more quickly
86
what happens to the membrane at 60-70 degrees? explain trend
further increase in temperature causes the membrane to be destroyed
ions/molecules diffuse first moments then reach equillibrium quickly
87
define diffusion
the net movement of substances from an area of high concentration to an area of low concentration, down a concentration gradient across a partially permeable membrane
88
what molecules diffuse through the bilayer?
-lipid soluble
-small
-non-polar molecules
89
what 4 factors affect the rate of diffusion?
-temperature
-concentration gradient
-thickness of exchange surface
-the surface area
90
explain how the thickness of exchange surface affects the rate of diffusion?
the thicker the exchange surface, the slower the rate of diffusion as there is a further length of diffusion pathway
91
explain how a concentration gradient affects the rate of diffusion?
if higher difference, there is a faster rate
92
what is Fricks laws - relative rate of diffusion formula?
(conc gradient x surface area) / length of diffusion pathway
93
define facilitated diffusion?
movement of substances from an area of high concentration to an area of low concentration, down a concentration gradient across the membrane via channel or carrier proteins
94
what is a channel protein?
act as pores in the membrane to allow specific ions through. eg Na
can be gated
95
what is a carrier protein?
proteins in the membrane that allow specific large molecules to pass through the membrane
96
how does a carrier protein work?
when the molecule binds to a specific site on the carrier, the protein changes shape and transfers the molecule to the other side of the membrane.
requires ATP
97
what 3 factors affect the rate of facilitated diffusion?
-temperature
-conc gradient
-number of carrier and channel proteins
98
define osmosis
movement of water from an area of higher water potential, to an area of lower water potential, down a concentration gradient across the phospholipid bilayer or via protein channels (aquaporins)
99
what is water potential measured in?
kilo pascals
100
whats the water potential of pure water?
0KPa
101
define hypertonic solution
lower water potential
i.e. lower conc of free water molecules than in the cell cytoplasm
102
define isotonic solution
same water potential as the cell
therefore no net movement of water molecules
103
define hypotonic solution
higher water potential
i.e. higher conc of free water molecules than in the cell cytoplasm
104
in an animal cell what does a hypotonic solution cause? and in a plant cell?
haemolysis
turgidity
105
in an animal cell what does a hypertonic solution cause? and in a plant cell?
crenation (shrivells)
plasmolysis/flaccid
106
define active transport
the active movement of ions or polar molecules from an area of lower concentration to an area of higher concentration using a carrier protein, against a concentration gradient
requires ATP
107
why is oxygen required for active transport?
since ATP is produced in respiration
108
what type of molecules are actively transported by carrier proteins?
non- lipid soluble
ions
large and water soluble (polar)
109
how is a one way flow ensured?
ATP changes the shape of the carrier protein in active transport and hence on one side of the membrane the shape of the protein will complement the specific molecule to be transported
once energy has been used by the protein carrier, it changes shape and releases the specific molecule ensuring a one way flow
110
what will prevent active transport?
anything that will inhibit ATP production
e.g. cyanide- a respiratory inhibitor which stops ATP production
111
describe/explain the process of co-transport in the lumen of the small intestine
1.the Na+/K+ pump actively transports Na+ out of the epithelial cell into the blood
2.this establishes a lower concentration of Na+ in the epithelial cell than in the lumen of the small intestine
3. Na+ move by fascilitated diffusion down a concentration gradient into an epithelial cell from the lumen
4. glucose moves into the epithelial cell with Na+ by co-transport/facilitated diffusion through co-transport protein
5.glucose moves into the blood from epithelial cell down a concentration gradient by facilitated diffusion
112
how a epithelial cells in the lumen adapted for a faster rate of diffusion?
-have microvilli lining the lumen, projections that stick out
-increased number of protein channels and carrier molecules in their membranes
113
define endocytosis
the bulk transport of substances into the cell
114
how is ATP used in endocytosis?
to move membrane to form vesicles to contain substances as it enters the cell
115
whats the role of the membrane during endocytosis?
-the membrane fuses together
-membrane engulfs the material
116
define exocytosis
the bulk transport of substances out of the cell
117
what is the use of ATP during exocytosis?
ATP is used to move the vesicle and allow it to fuse with the membrane to allow substances to leave the cell
118
describe two examples of bulk transport
-Hormones = pancreatic cells make and package insulin into vesicle in the golgi A. when the vesicle fuses with the membrane the insulin is released into the blood stream
-white blood cells = engulfing microorganisms by forming a vesicle around them and then allowing the vesicle to fuse with a lysosome in the WBC to allow digestion of the microorganism (phagocytosis)
119
what 3 ways can cells become specialised by, from switching of genes?
1. changing the shape of a cell= make have an increased SA
2. changing the number of a specific organelle e.g. a cell may have many mitochondria
3. changing the plasma membrane = may have more carrier proteins
120
how has a sperm cell adapted for its function?
- lots of mitochondria = needs a lot of energy for movement
- head contains enzymes = allows penetration of the female egg
- has a tail = propels the sperm towards the egg
121
how has a red blood cell adapted to its function?
-lacks organelles (such as nucleus) = to enable max space for haemoglobin
- biconcave = flexibility to fit through narrow capillaries
122
define tissues
collection of cells that are similar to each other and perform a similar function e.g. xylem tissue,nervous tissue
123
define organs
collection of tissues that work together to perform a particular function e.g. heart,lungs
124
define an organ system
group of organs working together e.g. respiratory system,digestive system
125
explain how cells are arranged in tissues in squamous?
-flattened cells, very thin
-line the inside of blood vessels and tubes to provide smooth surface for passage of fluids
thin walls provide a short diffusion pathway
126
explain how cells are arranged in tissues in ciliated epithelial tissue?
-column shaped cells
found on inner surface of the tubes e.g. trachea, bronchi
-goblet cells produce and secrete mucus.
-cilia can waft mucus when they move in a synchronised rythm
127
how does nicotine affect cilia?
can paralyse cilia and tar damage them so they cant sweep mucus out
128
Describe the procedure to prepare a slide
Add a drop of water to the slide
Remove a thin section of tissue and place it onto the slide (flat as possible)
Add 1 drop of iodine dissolved in potassium iodide to stain the sample (***This is only correct if it is plant tissue***)
Lower a coverslip on top using a mounting needle
129
Explain why it was important that the sections of tissue were thin
A thin section allows more light through;
allows a single layer of cells to be viewed.
130
Explain why you should push down hard on the cover slip, but should not push the cover slip sideways.
Push hard to squash the tissue to create a single layer of cells.
Do not push sideways as this will cause the cells to roll together.
131
A plant cell was observed with an optical microscope. Describe how the length of the cell could be estimated.
Use a stage micrometer to help us calibrate the size of the eyepiece graticule.
Measure the length of the plant cell with an eyepiece graticule.
132
Why are electron microscopes used to view cells?
They have a HIGH resolution
because electrons have a shorter wavelength than light.
This allows you to view internal structures/organelles of a cell.
(Remember using this – Light microscope = Low resolution = Longer wavelength)
133
describe the principles of the electron microscope
1. Electrons pass through / enter (thin) specimen;
2. Denser parts absorb more electrons;
3. (So) denser parts appear darker;
4. Electrons have short wavelength so give high resolution;
134
What is meant by ‘cell fractionation’ and why would scientists want to do it?
Separating out the contents of a cell into the different ‘fractions’ (i.e. different parts).
This usually means separating out the different organelles.
This is useful for scientists because it allows them to study individual organelles
135
When investigating diffusion or osmosis, you might want to make solutions of different concentrations. What is this called?
dilution series
136
What is a symport protein?
A type of cotransport protein.
A symport protein transports two substances through the membrane in the same direction together (like the Na+/glucose symport protein
137
What is an anti-port protein?
A type of cotransport protein.
An antiport protein transports two substances through the membrane in the opposite directions (e.g. the Na+/K+ pump)
138
Why is mitosis important? (4)
This is important for growth
replacement of old cells to repair body tissue
asexual reproduction
To make new daughter cells that contain exactly the same DNA has the original cell.
139
