5.1

Membranes are fluid mosaics of lipids and proteins with many functions- Gases and water can go through cellular membranes
Fluid mosaic models are models of cell membrane structure showing the proteins suspended in phospholipid fluid as a mosaic
- Shows structure and function
Diffusion and osmosis are forms of passive transport
Selective permeability is when a membrane only allows certain things to pass through
- Selective permeable membranes require proteins to regulate substances that enter and exit
  - Can you identify six different types of functions of proteins in a plasma membrane?

5.2

The spontaneous formation of membrane was a critical step in the origin of life
Phospholipids are the key ingredients in a biological membrane
- Probably first organic molecule to form
- Self-assemble into membranes
- Phospholipid bilayer form with phospholipids and water
- Membrane can enclose substance different than surrounding
  - In the origin of a cell, why would the formation of a simple lipid bilayer membrane not be sufficient? What else would have to be part of such a membrane?
    - Need proteins to regulate selective permeability

5.3

Passive transport is diffusion across a membrane with no energy investment
Diffusion is the tendency of molecules to spread out in available space
The area along where the density of a substance increases or decreases is called the concentration gradient
Equilibrium is what a substance strives for with diffusion
2+ substances diffuse separately
- - Why 2 molecules originally might go in seperate directions
  - Higher concentration on one side, lower concentration on the other, want to get to the lower concentration to attain equilibrium
Passive transport occurs across a membrane
Ions and polar molecules can diffuse across hydrophobic membranes by moving down in concentration gradient/if they have transport proteins
- - Why is diffusion across a membrane called passive transport?
  - It requires no energy from the cell, only uses kinetic energy

5.4

Osmosis is the diffusion of water across a membrane
Water is one of the most important substances to cross a membrane because...
- Water keeps the balance between a cell and environment
- Diffusion of water across selectively permeable membrane is called osmosis

5.5

Water balance between cells and their surroundings is crucial to organisms
Tonicity is the ability of the solution surrounding a membrane to make a cell gain or lose water
- Depends on concentration gradient
Cells are covered different solutions to monitor water movement
- Isotonic solutions ceases net water movement into or out of a cell
- Hypotonic solutions are solutions which cause cells to take in water
- Hypertonic solutions cause cells to expunge water
The control of water balance is called osmoregulation
Turgid: very firm (Non-woody plants need turgid cells for support)
Turgor pressure: back pressure
Flaccid: limp
Plasmolysis: plants losing water and shrivelling and pulling away from the cell wall

5.6

hydrophobic/polar molecules require transport proteins
Passive transport to move down the concentration gradient
- Facilitated diffusion is passive transport, moving down the concentration gradient
- Provides channel for specific molecules
- Carrier proteins carry proteins through phospholipid bilayer
Polar molecules diffusion (such as osmosis) is slow because the hydrophobic tails of the phospholipid bilayer

5.7

Research can lead to unplanned discoveries
Dr. Agre discovered abundant protein in cell membranes on accident
- Used frog eggs to test to see if protein made up water passageways to speed osmosis
- Theory seems to be true- named proteins aquaproteins
- Aquaporins allow only water to pass through
- Aquaporins can contribute to kidney, eye, and brain
  - Researching aquaporins can lead to medical solutions

5.8

Active transport moves a solute up its concentration gradient
- ATP provides energy for active transport
- Sodium Potassium pumps are a form of active transport
Active transport let’s cells keep different environments
Nerve signals depend on cell environment differences

5.9

Exocytosis release molecules from a cell through the cell membrane (EXIT)
Transport vesicles track:
- from golgi body
- Merges with plasma membrane
  - Pinocytosis
    - Cellular drinking
Endocytosis helps molecules enter the cell via the cell membrane
2 types of endocytosis:
- Phagocytosis: pseudopodia wrap around molecules
- Vacuole merges w/ lysosome
  - Digests molecules
  - “Cellular eating”
- receptor-mediated endocytosis: specific solute transports
  - Specific molecules trigger plasma membrane to indent and pinch closed around molecules, bringing them inside the cell
  - Can take in cholesterol for blood creation
  - Lipoproteins (LDL) bind to receptors
    - Enter endocytosis receptor-mediated endocytosis
    - Lack of LDL can lead to diseases
    - Because of build up of cholesterol

5.10

Forms of energy
- Energy capacity to cause change/to do work
  - Kinetic energy is the energy of motion
    - Motion onto matter
  - Potential energy is the energy all matter possesses
    - Water behind a dam
- Energy (like matter) is conserved
  - Cannot be created or destroyed
  - Every time energy is used, some is lost as heat
- Food provides covalent energy when bonds are broken
- Chemical energy potential energy could be released in chemical reaction
Energy Transformations
- Study of energy transformations = thermodynamics
  - 1st law of thermodynamics
    - Law of energy conservation
    - Energy in universe is consistent, forms change
- Recycling energy is impossible due to the give-off of heat
- Entropy is the measurement of disorder
- 2nd law of thermodynamics
  - Every energy conversion adds disorder aka entropy
- Cellular respiration is the chemical energy stored to make ATP

5.11

Exergonic reactions
- Energy outward
- Much potential energy used
- Reaction released energy equal in amount to which was used in reaction
Endergonic reactions
- Energy outward
- Little amount of potential energy
- Photosynthesis
Metabolism: total number of chemical reactions in an organism
Metabolic pathway: series of chemical reactions to build or break molecules
- EVERYTHING REQUIRES ENERGY
Coupling: use of energy from exergonic reactions

5.12

Atp:
- Adenosine triphosphate
- Negatively charged phosphate groups
  - Unstable bonds: breaks make ADP
  - Phosphate transfer from ATP to other molecule is called phosphorylation (powers endergonic synthesis)
- ATP makes active transport possible
- Renewable source: Cells regenerate ATP
  - - Energy from exergonic reaction → generates ATP
    - Endergonic bonding of phosphate to ADP → ATP
- 10 million ATP molecules per second

5.13

Enzymes speed chemical reactions by lowering energy barriers
- Energy has to be absorbed to break reactant bonds
- Activation energy: Amount of energy needed to make reactants less stable
- Activation energy prevents spontaneous breakdown of molecules- Break by adding heat
- Enzymes: molecules that increase reaction speed without being in the reaction
  - All enzymes are proteins, except RNA which can be an enzyme
  - Lower activation energy
  - Lower the barrier, faster the chemical reaction

5.14

Enzymes are specific for specific reactions: aka lock and key
Specific reactant for an enzyme labeled substrate
- Substrate fits into active site (indent on enzyme surface)
Catalytic Cycle
- Empty active site
- Substrate enters active site
- connection, known as induced fit can contort molecules
- Strained bond reacts with water, substrate converts into products
- Enzymes release products, do not change
- Single enzyme can act w/ millions of substrates per second
Optimal Conditions for Enzymes
- Shape affects substrate
- Temperature: rate of contact between reactants and acyive site
- Higher temps. denature/destroy function
  - Alter shape, substrates do not fit
- 6-8 ph for the same reasons as stated above
Cofactors
- Cofactors are non-proteins that assist enzymes
  - inorganic/non-living (ex. ions)
  - Organic cofactor = coenzyme
- All metabolic pathways function at once would create chemical chaos; cofactors regulate metabolism

5.15

Inhibitors limit enzyme activity
Competitive inhibitors block substrates from getting to the active sites
Non-competitive inhibitors do not block active site
Inhibitors regulate metabolism: overproduction leads to blockage feedback inhibitors

	Creado por Tessa Bushfield hace más de 6 años

9th grade Biology Apunte sobre Bio Chapter 5, creado por Tessa Bushfield el 12/12/2017.