Cellular structure and function (Chapter 3) Flashcards
1
Q
what are organelles in eukaryotic cells?
A
Eukaryotic cells have folded membranes and intracellular compartments called organelles.
2
Q
how can organelles help molecules?
A
This assists molecules to get to their desired destination.
3
Q
what do each organelle do?
A
- is responsible for a specific ‘task’.
- allow different chemical reactions to occur at the same time in different places without interfering with each other
- maintain concentration of molecules at levels that ensure reactants will collide with each other at optimal rates
4
Q
what is the role of the cell membrane?
A
- The boundary of a cell
- Determines cell identity
- Receives external signals
- Transports materials
5
Q
where is cell wall vs cell membrane?
A
- Cell wall is found in plant cell and cell membrane is found in both plant and animal cells.
- Cell membrane is covered by the cell wall which forms the outermost covering of plant cells
- Cell wall is completely permeable whereas cell membrane is semi-permeable.
- Cell wall is made up of cellulose and cell membrane is made up of lipids (fats) and proteins.
6
Q
what is the size of the cell/plasma membrane?
A
Plasma membranes range from 5 to 10 nm in thickness.
7
Q
size comparison to plasma membrane?
A
For comparison, human red blood cells, visible via light microscopy, are approximately 8 µm wide, or approximately 1,000 times wider than a plasma membrane. Can only be seen with a electron microscope.
8
Q
what do lipids include?
A
Fats and oils: important as energy-storing molecules
Phospholipids: important component of cell membranes
Steroids: hormones and vitamins
9
Q
lipids characteristics?
A
- Contain little water & insoluble in water (hydrophobic)
- Form effective barrier between two watery environments
10
Q
what is the cell membrane made of?
A
phospholipids
11
Q
what are phospholipids made of?
A
- 2 hydrophobic fatty acid hydrocarbon tails
- Hydrophilic phosphate group attached to the glycerol & other small groups to the phosphate
12
Q
what polarity is the phospholipid head?
A
hydrophilic polar head
13
Q
what polarity is the phospholipid tail?
A
hydrophobic non polar tail
14
Q
what is in the structure of the plasma membrane?
A
- transmembrane protein
- protein channel
- glycolipid
- cholesterol
- peripheral protein
- integral proteins
- carbohydrate hain
- phospholipid bilayer
- glycoprotein
15
Q
what model is the plasma membrane?
A
‘The fluid mosaic model’
16
Q
how is the plasma membrane a fluid mosaic model?
A
Comprises a phospholipid bilayer into which proteins & glycoproteins protrude
- Lipids are the ‘fluid’ part
- Proteins are the ‘mosaic’ part
- Membrane proteins have a variety of functions
Many proteins are glycoproteins
17
Q
what do some proteins in the plasma membrane form?
A
Some proteins form channels to assist the movement of materials into & out of cell
18
Q
what are the two types of proteins
A
- integral membrane proteins
- peripheral membrane proteins
19
Q
what are integral membrane proteins?
A
Integral membrane proteins, also called intrinsic proteins, have one or more segments that are embedded in the phospholipid bilayer.
20
Q
what are peripheral membrane proteins?
A
Peripheral membrane proteins, or extrinsic proteins, do not interact with the hydrophobic core of the phospholipid bilayer.
21
Q
what is the importance of the plasma membrane?
A
- Cells membranes have proteins called receptors that bind to signaling molecules and initiate a physiological response.
- Recognising ‘self’ and ‘non-self’
- Crossing the membrane
22
Q
why is the plasma membrane important for signalling?
A
Because membrane receptors interact with both extracellular signals and molecules within the cell, they can affect cell function without actually entering the cell.
23
Q
how does the plasma membrane recognise self or non self?
A
- on outer surface are substances called antigens (glycoproteins – signal receivers)
- a person’s antigens are unique to that person i.e. like a fingerprint
- antigens perform an important role in the immune system
24
Q
how permeable is the plasma membrane?
A
plasma membrane is semi-permeable or selectively permeable, therefore allowing only some dissolved materials to cross it
25
what does a selectively permeable cell membrane mean?
A selectively permeable cell membrane is one that allows certain molecules or ions to pass through it by means of active or passive transport.
26
what are factors governing substances crossing a membrane?
- Size
- Degree of polarity
- Not permeable to charged atoms (ions) and metallic ions
27
how does size affect permeability?
- Permeable to small molecules
- O2 (2 atoms), CO2 (3 atoms), ethanol (8 atoms), and H2O (3 atoms) due to its small size are permeable – but moves at a reduced rate
- Not permeable to larger hydrophilic polar molecules, e.g glucose (24 atoms)
28
how does degree of polarity affect permeability?
- Permeable to hydrophobic molecules
- May have receptors to help
29
what do charged atoms (ions) and metallic ions need to permeate the plasma membrane?
- Need channels
30
summary of how substances can permeate the plasma membrane?
- Lipid-soluble substances of various sizes, such as alcohol, are able to simply dissolve into the phospholipid bilayer and pass easily through membranes.
- Tiny molecules, such as water & urea, can pass between the phospholipid molecules.
- Small uncharged molecules, such as oxygen and carbon dioxide, can also pass through the phospholipid bilayer.
- Larger water-soluble substances, including amino acids and sugars, pass through channels made from protein molecules.
31
what can protein channels be?
Protein channels may be selective for particular substances, and may require energy for transport to occur.
32
what can permeate through the plasma membrane and examples?
- Gases (CO2, N2, O2)
- Small uncharged polar molecules (ethanol)
- water (H2O)
- urea (CH4 N2 O)
33
what can't permeate through the plasma membrane and examples?
- Large uncharged polar molecules (glucose)
- ions (K+, Mg2+, Ca2+, Cl-, HCO3-, HPO42-)
- Charged polar molecules (Amino acids, ATP, Glucose 6-phosphate)
34
what are the types of membrane transpot?
- passive transport (diffusion and facilitated diffusion)
- active transport
35
what is passive transport?
transport where no energy is required
36
what is active transport?
transport where energy is required (ATP)
37
what is simple diffusion?
The net movement of a substance from region of a high concentration to a region of low concentration.
38
what type of process is simple diffusion?
Simple diffusion is a passive process (no energy required)
39
what does diffusion do with concentration?
Diffusion moves solutes toward a concentration equilibrium.
40
what is the simple diffusion of water across a semipermeable membrane?
osmosis
41
define osmosis?
Osmosis is a special form of diffusion involving the movement of water across a semipermeable membrane
42
does cytoplasm have high or low water concentration?
Cytoplasm in cells has a relatively high water percentage (lots of water)
43
what happens if the environment outside the cell has a different percentage of water within the cell?
If the environment outside the cell has a different percentage of water, the water will diffuse in and out of the cell until equilibrium is reached and vice versa.
44
what are some key characteristics of osmosis and cells?
- Cells are all surrounded by a plasma membrane.
- Plasma membrane is fluid.
- It can change shape
- Depending on the outside conditions of a cell, the cell may swell or lose volume.
45
what is a hypertonic solution?
solute concentration inside the cell is lower
46
what happens when the solution is hypertonic?
water is transported out from the cell
47
what is a hypotonic solution?
solute concentration inside the cell is higher
48
what happens when the solution is hypotonic?
water is transported into the cell
49
what is a isotonic solution?
solute concentration inside the cell is equal to the solution outside the cell
50
what happens when the solution is isotonic?
amount of water transported into the cell equal to the amount of water transported out from the cell
51
what happens of osmosis in animal cells (red blood cells) when in an hypotonic solution (fresh water)?
A red blood cell will swell and undergo hemolysis (burst) when placed in a hypotonic solution.
52
what happens of osmosis in animal cells (red blood cells) when in an hypertonic solution (sea water)?
Then placed in a hypertonic solution, a red blood cell will lose water and undergo crenation (shrivel).
53
what happens of osmosis in animal cells (red blood cells) when in an isotonic solution?
no change in shape of cell, water moves in and out of the cell at the same rate
54
what happens of osmosis in plant cells when in an isotonic solution?
cell becomes flaccid
55
what is a flaccid plant cell?
A flaccid plant cell is not swollen and the cell membrane does not press against the cell wall tightly.
56
what happens of osmosis in plant cells when in an hypotonic solution?
cell becomes turgid
57
what is a turgid cell?
A turgid cell is a cell that has turgor pressure because water has entered.
58
what happens of osmosis in plant cells when in an hypertonic solution?
cell becomes plasmolysed
59
what is a plasmolysed cell?
A plasmolysed plant cell has lost water which causes cell contents to shrink away from the cell wall
- although the cell membrane maintain some contact with the cell wall
60
what are the two types of facilitated diffusion?
- Channel mediated
- Carrier mediated
61
what is channel mediated facilitated diffusion?
- can enter through protein channels
- faster than diffusion
62
what is carrier mediated facilitated diffusion?
- involves a specific carrier molecule assisting entry
- faster than diffusion
- carrier changes shape during transport
63
what process is active transport?
Endergonic process (requires energy)
64
how does active transport move with/against the concentration gradient?
Movement against a concentration gradient
65
what does active transport involve?
Involves a carrier protein for each substance actively transported
66
what are the proteins involved in active transport?
Proteins involved are generally called ‘pumps’. The proteins need to be coupled to an energy providing reaction (commonly the hydrolysis of ATP or the inward movement of proteins)
67
what is the speed of active transport in relation to other modes of transport?
Faster than diffusion
68
what is the importance of active transport?
- Uptake of essential nutrients against a concentration gradient.
- Allows secretory and waste products to be removed against the concentration gradient.
- Allows cells to maintain concentrations of ions in a non-equilibrium steady state.
69
what is bulk transport?
Bulk transport is a mode of transport of large quantities of materials and food particles across the membrane
70
what are the types of bulk transport?
- Exocytosis
- Endocytosis
71
what is exocytosis?
Type of bulk transport that moves large substances out of the cell
72
what are the steps involved in exocytosis?
1. Vesicular transport - a vesicle containing secretory products is transported to the plasma membrane
2. Fusion - the membranes of the vesicle and cell fuse
3. Release - the secretory products are released from the vesicle and out of the cell
73
what is exocytosis used for?
This is how hormones are secreted and how nerve cells communicate with each other
74
what is endocytosis?
Type of bulk transport that moves large substances into the cell
75
what are the steps involved in endocytosis?
1. Fold - plasma membrane folds inwards to form a cavity that fills with extracellular fluid and the target molecules
2. Trap - plasma membrane continues folding back on itself until the two ends of the membrane meet and fuse, trapping the target molecules inside the vesicle
3. Bud - the vesicle pinches off from the membrane and is transported to the appropriate cellular location
76
examples of endocytosis?
phagocytosis (solid material) and pinocytosis (liquid or dissolved substances)
