Mol Lecture #32

Question 1

Photosynthesis

Photosynthesis v.s. Cellular Respiration (comparison)

Answer 1

• Use calvin cycle to fix carbon into organic molecules
• Use H2O and CO2 are the reactants and products are O2 and sugars
• Only occurs in plants (and other photosynthetic organisms)
• Photosynthesis stores energy
• Glucose (via G3P in photosynthesis) and O2 are the reactants of CR and the products of photosynthesis

G3P is common to both

Question 2

CR

Photosynthesis v.s. Cellular Respiration (comparison)

Answer 2

• Cellular respiration happens in all eukaryotic cells
• Something like it is going to happen in prokaryotes as well
• Cellular respiration releases energy
• The products of cellular respiration are the reactants of photosynthesis

G3P is common to both

Question 3

Overview

Membranes

Answer 3

• Membranes provide a selective permeability barrier for cells and organelles
• Made up of: lipids + proteins
  → important place for permeability control (permeability barrier that we can regulate)
  → membranes contain proteins that are responsible for permeability control as well as communication with other cells and the outside environment.
• Membranes also contain enzymes (proteins with enzymatic activity)

Question 4

Phospholipids

Answer 4

• Polar head group can be variable (polar alcohol)
• Variability in the length and saturated aspects of the tails (number of double bonds) - changes the properties of the phospholipids and properties of the membrane in general.
• Membrane is strong because it has a polar region and a non-polar region (highly amphipathic molecule)
  → hydrocarbons face each other, while head groups (on both sides) face aqueous solution.

Question 5

Cholesterol

Answer 5

• (another) Main lipid of the membrane
• Has the hydrophilic end and hydrophobic inner end + tail
  -Cholesterol has a highly rigid structure that enhances the selective barrier properties of the membrane.
• (also) Helps to keep the membrane in a packed and oragnized state; especially during temp. fluctuations.

Question 6

Cholestrol in the membrane

at high v.s. low temp.’s

Answer 6

• At high temperatures, cholestrol molecules position themselves in a way that makes the membrane less deformable. (at high temperatures phospholipids tend to move around a lot, that can cause breaks in the membrane, but cholesterol regulates that)
• At low temperatures, cholesterol molecules prevent membranes from freezing interfering with crystalization interactions of the phospholipid tails.

Question 7

Proteins in the Bilayer

Types

Answer 7

• Transport proteins
• Recognition proteins
• Receptor proteins (allow the cell to interact with the environment)
• Cell adhesion proteins (mediate interactions with cells and their environment- allowing sticking to surfaces)
• Enzymes

Question 8

Proteins in the Bilayer

Structure

Answer 8

• For a protein to go through the membrane it would need to have hydrophilic and hydrophobic properties
• Amino acids sticking out (inside the membrane) are hydrophobic, and the channels are hydrophilic + surface sticking out.
• Secondary structure mediated by hydrogen bonds within the backbone (also interacting with the membrane) (alpha helix)

Question 9

Fluid Mosaic Model

Answer 9

• Proteins that are integral (inside the membrane) or peripheral proteins (hanging outside)
• Some lipids and proteins move freely within the membrane, those that are not are apart of the cytoskeleton.

Question 10

The Frye-Eddin Experiment

Answer 10

• Proof: that proteins are able to mix (proteins moving within a certain time-period)

Question 11

Membranes in Eukaryotic cells

Answer 11

• Talking about the membranes on the outside of the cell as well as the organelles

Question 12

Membrane Permeability and Transport

Answer 12

• Permeability is based on the size and charge of the entity that we’re talking about.
• Very small molecules that are non-polar can pass freely
• Increases in either size or polarity will decrease the permeability of that entity.
  → water can cross at some rate
• Transport describes the process through which different molecules get across membranes

Question 13

Passive Transport

(Overview)

Answer 13

• Type of transport that doesn’t require direct energy input
• Specific (especially when mediated by proteins)
• Directional
• Fully dictated by the concentration of the entity on both sides of the membrane ( []= concentration)
• Difference in concentration provides the energy. A concentration gradient that stores potential energy (see this in ATP synthase)

Question 14

Passive Transport

Diffusion

Answer 14

• The property whereby molecules or ions move from an area of higher concentration to an area of lower concentration. (again, H+ ions in oxidative phosphorylation)

Question 15

Two types of diffusion:

Answer 15

i. Simple diffusion
- Small nonpolar molecules pass through the membrane directly (also water)
ii. Facilitated diffusion
- Protein mediated transport of molecules or ions across a membrane. Usually a highly selective pathway.

Question 16

Osmosis

Answer 16

• diffusion of water