Lecture 3 - Molecules of Life: Carbs, Lipids, Membranes

Question 1

Major roles of carbohydrates (3)

Answer 1

1. source of stored energy.
2. transport stored energy.
3. serve as carbon skeletons for other molecules.

Question 2

Categories of carbohydrates (4)

Answer 2

• 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)

Question 3

Carbohydrate chemical name

Answer 3

CmH2nOn

Question 4

Properties of glucose (3)

Answer 4

• 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.

Question 5

Monosaccharides have ___ number of carbons

Answer 5

different

• hexoses (6C) like fructose, galactose
• pentoses (5C) like ribose, deoxyribose

Question 6

Glycosidic linkages (3)

Answer 6

• bond monosaccharides convalently to form di-, oligo-, or polysaccharides.
• via condensation reactions: forms ether.
• alpha (down) or beta (up)

Question 7

Polysaccharides are important for…

Answer 7

energy storage and structure.

Question 8

Three types of Polysaccharides:

Answer 8

1. Starch: storage of glucose in plants. (branched, limited H-bonds, less compact)
2. Glycogen: storage of glucose in animals, in liver and muscle. (highly branched, more compact than starch)
3. Cellulose: most abundant organic on Earth, in plant cell wall, compact & dense, H-bonds between chains. (linear, parallel polymers of glucose molecules, really compact).

Question 9

Lipids (4)

Answer 9

• nonpolar, hydrocarbons (no oxygens, just carbons and hydrogens)
• insoluble in water
• if close, weak but additive VDW forces hold together
• not polymers

Question 10

Seven types of Lipids:

Answer 10

1. Fats and oils: store energy
2. Phospholipids: cell membrane
3. Carotenoids and Chrlorophylls: capture light energy (plants)
4. Steroids and modified fatty acids: hormones and vitamins
5. Animal fat: thermal insulation
6. Lipid coating around nerves: electrical insulation
7. Oil or wax: repels water (skin, fur, feathers), prevents water evaporation.

Question 11

Triglycerides (3)

Answer 11

• 3 fatty acids and 1 glycerol
• connected by ester bond between carboxyl and hydroxyl
• simple lipid (solid fat at 20oC, liquid oil at 20oC)

Question 12

Fatty acids may be ____ and ____

Answer 12

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.

Question 13

Fatty acids are NOT completely ___. They are ___. (3)

Answer 13

hydrophobic, amphipathic.

• they have opposing chemical properties
• when carboxyl ionizes, it forms COO- which is strongly hydrophillic.
• The tail is hydrophobic.

Question 14

Phospholipids are ___. (3)

Answer 14

• 1 phosphate group, 1 glycerol, 2 fatty acids (glycerol and fatty acids bound by ester linkage)
• head has charge
• tails are nonpolar

Question 15

Phospholipids in water form…

Answer 15

phospholipid bilayer.

triglycerides cannot form bilayer because they do not have polar heads.

Question 16

Other lipids (4)

Answer 16

• 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.

Question 17

Study membranes by (3)

Answer 17

1. freeze structure membrane
2. separate along the weak hydrophobic interfaces
3. proteins seen as “bumps”

Question 18

Membranes are Fluid Mosaic Model (3)

Answer 18

• Phospholipids: form hydrophobic core (barrier)
• Proteins: noncovalently embedded
• Carbohydrates: attached to lipids or proteins and are located outside of the cell; recognize other cells.

Question 19

Phospholipid bilayer (2)

Answer 19

• fatty acid “tails” interact with each other.
  
  • interior is somewhat fluid which allows for lateral movement.
• Polar “heads” face aqueous environment.

Question 20

Membrane fluidity is affected by (2)

Answer 20

1. Lipid composition:
   
   • close packing, saturated fatty acids = less fluid
   • unsaturated or shorter fatty acids or less cholesterol = more fluid.
2. Temperature:
   
   • low = less fluid
   • high = more fluid

Question 21

Three types of membrane proteins:

Answer 21

1. Peripheral: not embedded in bilayer, contain polar or charged regions.
2. Integral: partially embedded in bilayer
3. Transmembrane: integral proteins that span bilayer and protrudes both sides.

Question 22

Membrane surface carbohydrates are _____ sites. (2)

Answer 22

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.

Question 23

Cells recognize each other by (2)

Answer 23

• cell recognition: specific interaction between cells

- cell adhesion: connection between two cells is strengthened.

Question 24

Homotypic and Heterotypic:

Answer 24

Homotypic: same molecules in both cells
Heterotypic: binding of different molecules on different cells.

Question 25

___ ______ connect adjacent cells.

Answer 25

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)

Question 26

Integrins (2)

Answer 26

• attach epithelial cells to extracellular matrix (noncovalent and reversible)
• as one side of cell detaches, the other side extends in direction of movement.

Question 27

Membrane Transport (3)

Answer 27

• 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.

Question 28

Simple diffusion (3)

Answer 28

• random movement to equilibrium.
• net movement is directional [high] to [low]
• occurs through phospholipid bilayer: hydrophobic molecules pass, polar molecules do not pass.

Question 29

Osmosis (2)

Answer 29

• diffusion of water across membranes - depends on [water]
• hypertonic: high [solute]
  isotonic: equal solute
  hypotonic: low [solute]

Question 30

Aquaporins (defn)

Answer 30

integral proteins that allow passage of water across phospholipid bilayer to speed up water diffusion.

Question 31

Facilitated diffusion (defn)

Answer 31

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)

Question 32

Active transport (3)

Answer 32

• “against the normal flow” [low] to [high]
• requires ATP (energy)
• directional (either in or out of cell, depending on need)

Question 33

Two types of active transport:

Answer 33

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)

Question 34

Sodium-potassium pump (4 steps)

Answer 34

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.

Question 35

Active transport of Glucose (2 steps)

Answer 35

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.

Question 36

Endocytosis and Exocytosis:

Answer 36

Large substances enter and leave via membrane vesicles. Plasma membrane folds in during endocytosis and out during exocytosis.

Question 37

Three types of endocytosis:

Answer 37

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.

Question 38

Receptor-mediated endocytosis (4)

Answer 38

• 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