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LAMC Bio 3 Lecture Notes: Chapter 5 – The Working
Cell
Reading Assignment: Chapter
5
Learning
Outcomes:
By the end of today’s lecture, you should be able to
explain:
- the 1st and 2nd laws of thermodynamics
- endergonic and exergonic reactions
- the role of enzymes in chemical reactions
- the role of the plasma membrane in cell activities
- passive and active transport
- how water balance affects plant and animal cells
- endocytosis and exosytosis
I. Cell Energy:
Energy – the
capacity to perform work
Kinetic energy – the energy of
motion
Potential energy – stored energy
that an object has due to its structure or location
Chemical energy – the potential
energy of molecules
1st Law of Thermodynamics:
the total amount of energy in the universe if constant.
2nd Law of Thermodynamics: energy
conversions reduce the order of the universe and increase its entropy (amount of
disorder in a system).
Endergonic reactions – requires a
net input of energy (e.g. the production of glucose through photosynthesis)
Exergonic reactions – provides a
net release of energy (e.g. cellular respiration that breaks down glucose)
ATP shuttles chemical energy and drives cellular work.
II. Enzymes:
Enzyme - a
protein molecule that functions as a biological catalyst, increasing the rate of
reaction without itself being changed into a different molecule; it speeds up a
reaction by lowering the EA barrier.
Energy of activation (EA)
- the amount of energy that reactants must absorb to become activated and start
a chemical reaction.
Enzymes are reaction specific. A substrate
is a specific reactant that an enzyme acts on.
The active site is the region
of the enzyme that the substrate fits into.
Enzyme inhibitors can block enzyme action. A
competitor inhibitor competes with
the substrate for the active site on the enzyme.
A noncompetitive inhibitor binds to the enzyme and changes the shape
of the active site.
III. Plasma membrane structure and function:
The plasma membrane has selective
permeability; it allows some substances to cross more easily than others.
Many membrane proteins are enzymes and function as reaction catalysts, receptors
for signal transduction, and transport of molecules across the membrane.
Passive transport – the diffusion
of molecules down their concentration gradient until equilibrium is reached;
doesn’t require energy expenditure by the cell.
Facilitated diffusion – the
diffusion of molecules across a membrane with the help of transport proteins;
doesn’t require energy expenditure by the cell.
Osmosis – diffusion of water across
a membrane
Active transport – movement of a
solute across a membrane against its concentration gradient; requires
energy expenditure by the cell.
Tonicity – the tendency of a cell
in a given solution to lose or gain water.
Isotonic – the cell and surrounding
solution have the same solute concentration (cell doesn’t gain or lose water)
Hypotonic – the surrounding
solution has a lower solute concentration than the cell (the cell gains water)
Hypertonic - the surrounding solution
has a higher solute concentration than the cell (the cell loses water)
Osmoregulation – the control of
water balance in organisms (e.g. fish in freshwater and saltwater)
Exocytosis - the process used by
cells to transport large materials out of the cell
Endocytosis - the process used by
cells to transport large materials into the cell
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