The Cell and Homeostasis

Honors Biology

Chapter 5

I. NRG

• Ability to do work

A. Types of nrg (2)

1. Kinetic – – Nrg of motion– Transfers motion to other matter

ex. Muscles contract and move body parts which in turn moves obejcts

2. Potential nrgStored nrg object has due to location or structure

Ex. Nrg stored in chemical bonds, when broken releases power to do work

II. Chemical Reactions and nrg

• Chemical rx either store or release nrg

Types of chemical rx:

A. Endergonic rx = nrg in

nrg absorbed from environment as rx occurs

so product stores nrg within bonds

Ex. photosynthesis

B. Exergonic rx = nrg outchemical reactions that release nrg

Ex. Wood burning, cellular respiration

Ex. Of both types of reactions:

combination of endergonic and exergonic reaction is one that stores and releases nrg to be used by all living organisms

Ex. We eat food – it gets broken down chemically = what is not used is stored to be used later

III. WorkWork = rearrangement of matter

(need nrg to do this sometimes)

3 types of work

A. chemical

B. mechanical

C. transportation

A. Chemical work

Chemical nrg –

nrg for cell activity

need ATP to do this

Structure of ATP

Adenine + ribose + 3 phosphates

Adenine + ribose = adenosine

ATPHigh energy bonds when broken release a lot of nrg

Process of breaking bonds of ATP = Dephosphorylation

Dephosphorylation = exergonic reaction used by cells to get nrg need

Phosphorylation –

“popping P back on”

Endergonic reaction used to store nrg not used by the body at the time

B. Mechanical Work

Mechanical work –

•transfer phosphate to a protein in muscle which will cause muscle to contract

•contraction is the mechanical work done by using the chemical nrg

c. Transport work

Transport work:

•Phosphate (of ATP) attaches to protein on cell membrane used to transport molecules across the cell membrane

IV. Enzymes

Enzyme-

•protein that catalyzes a chemical reaction without being changed itself

•Doesn’t add nrg to reaction, it speeds it up by lowering the amount of nrg needed to start the reaction (activation nrg)

•Nrg absorbed to weaken bonds so they break

B. Enzyme specificity

• Remember each protein has it’s own shape and that shape determines which chemical reaction the enzyme will catalyze

C. Steps of catalyzing (Induced Fit model)

Steps: (this should be a review for you)

1.Substrate binds to enzyme at active site - Substrate – molecule enzyme is acting on- Active site – region where substrate fits

into enzyme

2. Active site changes shape to hold onto substrate better (creates induced fit)

2. The induced fit weakens bonds

2. Substrate converted to new products

2. products released

d. Cell environment can effect enzyme

4 things can effect activity of enzyme within cell

a.Temperature of cell –

higher temp. destroy enzymes by altering

shape (denaturing)

b. pH - most enzymes function between 6-8 pHif not in this range it denatures

c.Salt concentration – salt ions interfere with some chemical bonds that maintain shape of enzymes.

d. Coenzymes / cofactors

coenzymes = organic molecules that help

the enzyme

Cofactors = inorganic molecules that help

the enzyme

E. Enzyme InhibitorsEnzyme inhibitors interfere with enzymes activities by attaching to the enzyme and preventing it from working.

Toxins, poisons, and pesticides all do this

Ex. Cyanide – stops production of ATP by inhibiting the enzyme that produces ATP

Ex. Ibuprofen / aspirin- interfere with enymes that induce pain

2 types of enzyme inhibitors

1. Competitive – fits into active site and blocks substrate, so enzyme doesn’t work

2. Noncompetitive – binds to enzyme at place other then active site and changes shape of the enzyme so it doesn’t work

V. Molecular Transportation

• Cell membrane is a bilayer of phospholipids with protein, carbohydrates and cholesterol

• It is selectively permeable, therefore not everything can enter or exit the cell

• Semi permeability helps maintain homeostasis of the cell

Factors determine cell membrane transportation

• Size

• Shape

• solubility

a. 2 types of Membrane Transportation

• A. Passive

• B. Active

A. Passive Transportation

• Diffusion

• Osmosis

• Facilitated Diffusion

• Ion channels

1. Diffusion

• Movement of molecules from an area of high to low concentration

• Depends on concentration gradient

• Moves down gradient

Concentration gradient

• http://www.indiana.edu/~phys215/lecture/lecnotes/lecgraphics/diffusion.gif

2. Facilitated Diffusion

• Protein carrier• High to low• Steps:

– Molecule binds to specific protein– Protein changes shape– Carrier releases molecule – Returns back to original shape

3. Osmosis

• Diffusion of WATER ONLY from an area of high to low concenration

• Depends on concentration of solutes on both sides of membrane

3 ways water moves

• Hypertonic solution - more solutes outside the cell membrane- water diffuses out of cell and cell shrinks

• Hypotonic solution - less solutes outside the cell membrane- water diffuses into cell and the cell explodes

• Isotonic solution - same solutes outside as inside the cell

- equal water movement

4. Ion Channels

• Integral proteins• Passageway because insoluble to

membrane• Specific ion channels for each ion• Some gated - some open all time• Gates respond to different signals -

electrical, chemical, cell membrane stretching

B. Active Transportation

• Nrg

• Against concentration gradient

Types of Active Transportation

1. Pumps

2. Vesicular

1. Cell membrane pumps

• Carrier protein (integral)• Against concent. Gradient• Steps for Na+/K+ pump)

– 3 Na+ inside cell binds to carrier protein – Protein changes shape– Na+ released outside cell– 2 K+ picked up outside cell – Protein changes shape– 2 K released inside cell– (3Na+ out - 2 K+ inside)

Na+ / K+ pump

Na+ / K+ pump

• Maintains electrochemical gradient (outside cell membrane more positive compared to inside)

• Maintains neg. charge inside the cell• This allows cell to function properly• If too positive inside, muscles won’t

contract, neurons won’t fire, etc…• This is homeostasis for inside of cell

Vesicular Transportation

• Exocytosis

• Endocytosis

2. Exocytosis

• Exo = out

• Cytosis = cell

• Exocytosis = to bring materials out of the cell

Process of exocytosis• Vessicle merges with cell membrane

• Cell membrane opens and contents are released

• Ex. Protein made on RER sent to golgi where it is modified packaged and shipped to cell membrane, vesicle fuses with membrane and vesicle releases to go to other cells

3. Endocytosis

• Endo = into

• Cytosis = cell

• Movement of molecules INTO the cell

Process of endocytosis

• Molecules engulfed by the cell membrane

• Form a vesicle around the macromolecule

• Vesicle pinched off inside cell

• Lysosome breaks down and releases contents into cell

Types of Endocytosis

a. Pinocytosis – To bring water into the cell

b. Phagocytosis – To bring solids into the cell

c.Receptor mediated -

plasma membrane indents where receptors activated and create vesicle which is brought into the cell

Videos

• Check on my wiki site for videos to watch regarding cell transportation