Lecture 3 - Molecules of Life: Carbs, Lipids, Membranes Flashcards
1
Q
Major roles of carbohydrates (3)
A
- source of stored energy.
- transport stored energy.
- serve as carbon skeletons for other molecules.
2
Q
Categories of carbohydrates (4)
A
- monosaccharides (simple sugars)
- disaccharides (2 simple sugars linked by covalent bonds)
- oligosaccharides (3 to 20 monosaccharides, ex. ABO blood groups)
- polysaccharides (hundreds to thousands of monosaccharides)
3
Q
Carbohydrate chemical name
A
CmH2nOn
4
Q
Properties of glucose (3)
A
- energy source for all cells.
- exist as straight chain or ring (ring is more common due to superior stability)
- ring exists as alpha or beta glucose.
5
Q
Monosaccharides have ___ number of carbons
A
different
- hexoses (6C) like fructose, galactose
- pentoses (5C) like ribose, deoxyribose
6
Q
Glycosidic linkages (3)
A
- bond monosaccharides convalently to form di-, oligo-, or polysaccharides.
- via condensation reactions: forms ether.
- alpha (down) or beta (up)
7
Q
Polysaccharides are important for…
A
energy storage and structure.
8
Q
Three types of Polysaccharides:
A
- Starch: storage of glucose in plants. (branched, limited H-bonds, less compact)
- Glycogen: storage of glucose in animals, in liver and muscle. (highly branched, more compact than starch)
- Cellulose: most abundant organic on Earth, in plant cell wall, compact & dense, H-bonds between chains. (linear, parallel polymers of glucose molecules, really compact).
9
Q
Lipids (4)
A
- nonpolar, hydrocarbons (no oxygens, just carbons and hydrogens)
- insoluble in water
- if close, weak but additive VDW forces hold together
- not polymers
10
Q
Seven types of Lipids:
A
- Fats and oils: store energy
- Phospholipids: cell membrane
- Carotenoids and Chrlorophylls: capture light energy (plants)
- Steroids and modified fatty acids: hormones and vitamins
- Animal fat: thermal insulation
- Lipid coating around nerves: electrical insulation
- Oil or wax: repels water (skin, fur, feathers), prevents water evaporation.
11
Q
Triglycerides (3)
A
- 3 fatty acids and 1 glycerol
- connected by ester bond between carboxyl and hydroxyl
- simple lipid (solid fat at 20oC, liquid oil at 20oC)
12
Q
Fatty acids may be ____ and ____
A
Saturated: no double bonds - saturated with hydrogen - straight, packed tightly - animal fats - high melting point Unsaturated: one or more double bonds - kinks in molecule prevent packing - plant oils - low melting point.
13
Q
Fatty acids are NOT completely ___. They are ___. (3)
A
hydrophobic, amphipathic.
- they have opposing chemical properties
- when carboxyl ionizes, it forms COO- which is strongly hydrophillic.
- The tail is hydrophobic.
14
Q
Phospholipids are ___. (3)
A
- 1 phosphate group, 1 glycerol, 2 fatty acids (glycerol and fatty acids bound by ester linkage)
- head has charge
- tails are nonpolar
15
Q
Phospholipids in water form…
A
phospholipid bilayer.
triglycerides cannot form bilayer because they do not have polar heads.
16
Q
Other lipids (4)
A
- carotenoids: light absorbing pigments
- steroids: cholesterol (in 25% of cell membrane) and hormones
- vitamins: small, acquired in diet
- waxes: highly nonpolar and impermeable to water.
17
Q
Study membranes by (3)
A
- freeze structure membrane
- separate along the weak hydrophobic interfaces
- proteins seen as “bumps”
18
Q
Membranes are Fluid Mosaic Model (3)
A
- Phospholipids: form hydrophobic core (barrier)
- Proteins: noncovalently embedded
- Carbohydrates: attached to lipids or proteins and are located outside of the cell; recognize other cells.
19
Q
Phospholipid bilayer (2)
A
- fatty acid “tails” interact with each other.
- interior is somewhat fluid which allows for lateral movement.
- Polar “heads” face aqueous environment.
20
Q
Membrane fluidity is affected by (2)
A
- Lipid composition:
- close packing, saturated fatty acids = less fluid
- unsaturated or shorter fatty acids or less cholesterol = more fluid.
- Temperature:
- low = less fluid
- high = more fluid
21
Q
Three types of membrane proteins:
A
- Peripheral: not embedded in bilayer, contain polar or charged regions.
- Integral: partially embedded in bilayer
- Transmembrane: integral proteins that span bilayer and protrudes both sides.
22
Q
Membrane surface carbohydrates are _____ sites. (2)
A
recognition.
- Glycolipids: carbohydrate bound to lipid used for recognition for interaction with other cells.
- Glycoproteins: carbohydrate bound to protein used for cell recognition and adhesion.
23
Q
Cells recognize each other by (2)
A
- cell recognition: specific interaction between cells
- cell adhesion: connection between two cells is strengthened.
24
Q
Homotypic and Heterotypic:
A
Homotypic: same molecules in both cells
Heterotypic: binding of different molecules on different cells.
25
___ ______ connect adjacent cells.
Cell Junctions.
- tight junctions: prevent movement of substances (ex. bladder cells)
- desmosomes: hold cells firmly together, material still move in intracellular space (ex. skin cells)
- gap junctions: channels between cells (ex. heart muscle cells)
26
Integrins (2)
- attach epithelial cells to extracellular matrix (noncovalent and reversible)
- as one side of cell detaches, the other side extends in direction of movement.
27
Membrane Transport (3)
- Selective Permeability: some substances pass while others are permitted.
- Passive: Simple diffusion, osmosis, facilitated diffusion. No energy required, energy comes from concentration gradient.
- Active: input of chemical energy required.
28
Simple diffusion (3)
- random movement to equilibrium.
- net movement is directional [high] to [low]
- occurs through phospholipid bilayer: hydrophobic molecules pass, polar molecules do not pass.
29
Osmosis (2)
- diffusion of water across membranes - depends on [water]
- hypertonic: high [solute]
isotonic: equal solute
hypotonic: low [solute]
30
Aquaporins (defn)
integral proteins that allow passage of water across phospholipid bilayer to speed up water diffusion.
31
Facilitated diffusion (defn)
carried out by channel proteins that are activated by high concentration of solute and a stimulus molecule (ligand) to allow passage of polar molecules across membrane and into cell.
also carried out by carrier proteins (glucose carrier protein)
32
Active transport (3)
- "against the normal flow" [low] to [high]
- requires ATP (energy)
- directional (either in or out of cell, depending on need)
33
Two types of active transport:
1. Primary: direct hydrolysis of ATP provide energy for transport (ex. Sodium-Potassium pump)
2. Secondary: doesn't use ATP directly; instead energy is supplied by [ion] gradient established by primary active transport (ex. Glucose transport)
34
Sodium-potassium pump (4 steps)
1. 3 Na+ and 1 ATP bind to the protein pump.
2. Hydrolysis of ATP phosphorylates the pump and changes its shape.
3. The shape change allows sodium to be released and potassium ions to bind to the pump.
4. Release of phosphate reverts pump shape and releases potassium ions into cell and exposing sodium binding sites.
35
Active transport of Glucose (2 steps)
1. After Na-K pump releases sodium, outside of cell has high [Na+].
2. High [Na+] drives glucose into its glucose symporter channel and releases glucose into interior of cell.
36
Endocytosis and Exocytosis:
Large substances enter and leave via membrane vesicles. Plasma membrane folds in during endocytosis and out during exocytosis.
37
Three types of endocytosis:
1. Phagocytosis (nonspecific): "cellular eating", large particles or cells.
2. Pinocytosis (nonspecific): "cellular drinking", small vesicles filled with dissolved substances.
3. Receptor-mediated (highly specific): molecules at cell surface recognize and trigger uptake of specific materials.
38
Receptor-mediated endocytosis (4)
- there are specific receptor proteins on membrane
- specific substances bind to receptor proteins.
- coated pit forms with clathrin molecules
- coated vesicle breaks off from membrane
