LIFESCI 7A (F26): AOL #1

Chemistry of Life, Cell Organization and Membranes, Membrane Transport, Energy and Enzymes

Describe the structure of an atom.

The center of the atom, called the nucleus, contains positively charged protons and neutrally charged neutrons. Floating around the nucleus in orbitals are negatively charged electrons.

Explain how nonpolar and polar covalent bonds are formed between atoms.

Covalent bonds are formed between two non-metals or metalloids and involve the sharing of electrons. In nonpolar covalent bonds, electrons are shared equally. In polar covalent bonds, the more electronegative atom will pull the electrons closer to itself, so the electrons are shared unequally.

Explain how the potential energy of two atoms changes as they form or break a bond.

As two atoms approach each other, their potential energy decreases because they are getting closer and closer to forming a bond and reaching the most stable state. Breaking a bond increases potential energy because energy is needed to counteract the attractive forces between the molecules.

electronegativity

an atom’s ability to attract electrons

polarity

• uneven distribution of electrons across a molecule

• when polar covalent bonds are formed, the electronegative atom gains a partially negative charge due to accumulation of electrons

ionic bonds

• between ions with very different charges and electronegativities

• electrons transfer from metal to nonmetal

hydrogen bonds

intermolecular force between partially postive hydrogen and partially negative other electronegative atomav

van der waals forces

• intermolecular force due to random accumulation of electrons on one part of an atom to create temporary charge

• can be between any atoms/molecules

hydrophilic

polar, attracted to water

hydrophobic

nonpolar, avoidant of water

How many covalent bonds can H form?

1

How many covalent bonds can C form?

4

How many covalent bonds can O form?

2

How many covalent bonds can N form?

3

Compare and contrast the relative electronegativities of H, C, O, and N.

H=C<O=N

Relate the potential energy change of an atomic interaction to its “strength”.

Bonds with lower potential energy are stronger than bonds with higher potential energy.

What features do eukaryotic cells have that prokaryotic cells do not?

• internal compartmentalization

• nucleus

What organelles do plant cells have that animal cells do not?

• cell wall

• plasmodesmata

• central vacuole

• chloroplasts

What is the difference between saturated and unsaturated fatty acids?

Unsaturated fatty acids contain C=C bonds, which cause a kink in the hydrocarbon chain. This prevents the fatty acids from packing too tightly together.

Saturated fatty acids don’t have any double bonds, so all the carbons are fully saturated with hydrogens. This means that they can pack very tightly together.

Describe the structure of the plasma membrane.

The plasma membrane is made of a phospholipid bilayer, where the hydrophilic phosphate heads face the outside aqueous environments, and the hydrophobic fatty acid tails face each other to avoid the aqueous environments.

organelle

an internal compartment within the cell that performs a specific function

cytoplasm

everything between the cell membrane and the nuclear envelope (including organelles)

cytosol

jelly-like substance inside the cell that surrounds the organelles

mitochondria

converts energy from sugars into ATP

chloroplast

converts chemical energy from sunlight into sugars, only present in plant cells

nucleus

stores DNA

endoplasmic reticulum

produces and transports proteins/lipids

Golgi apparatus

modifies and sorts proteins/lipids from the ER

lysosomes

degrade damaged cellular material and waste

vacuole

maintains turgor pressure against cell wall

triglyceride

• three fatty acid chains connected to a glycerol molecule

• aka triacylglycerolaf

fatty acid

long chain of carbons connected to a carboxyl group

phospholipid

hydrophilic phosphate head attached to two hydrophobic fatty acid tails

cholesterol

• type of steroid

• hydrophobic

• four fused rings

• acts as a buffer to help maintain membrane fluidity

amphipathic

molecule that contains both polar and nonpolar regions

integral proteins

proteins embedded in the membrane

peripheral proteins

proteins that are temporarily associated with the membrane

transmembrane proteins

integral proteins that span the entire width of the membrane

How does temperature affect membrane fluidity?

• increasing temperature = increasing fluidity

• decreasing temperature = decreasing fluidity

How does phospholipid chain length affect membrane fluidity?

• longer phospholipid chains = less membrane fluidity (more van der waals forces)

• shorter phospholipid chains = more membrane fluidity

How does phospholipid saturation affect membrane fluidity?

• more saturated fatty acids/less unsaturated fatty acids = less fluid

• less saturated fatty acids/more unsaturated fatty acids = more fluid

How do the phospholipid bilayer’s chemical properties allow it to act as a semipermeable membrane?

The hydrophilic exteriors allow the membrane to separate the aqueous extracellular and intracellular environments.

The hydrophobic interior ensures that only small, nonpolar molecules are able to pass through without help from specific transport proteins.

diffusion

substance moves with the concentration gradient (high to low)

tonicity

ability of a solution to make water move in or out of a cell by osmosis

osmosis

• the net movement of water (or another solvent) across a selectively permeable membrane towards the side with higher solute concentration

• high water concentration —> low water concentration

hypertonic (side A is hypertonic to side B)

side A has a higher solute concentration (lower water concentration) than side B

hypotonic (side A is hypotonic to side B)

side A has a lower solute concentration (higher water concentration) than side B

isotonic (side A is isotonic to side B)

side A has the same solute concentration (and thus water concentration) as side B

simple diffusion

• transports substance from higher concentration to lower concentration (with gradient)

• no energy required

• no membrane protein needed

• additional random movement in both directions occurs when both concentrations are equal, but no net movement

facilitated diffusion

• transports substance from higher concentration to lower concentration (with gradient)

• no energy required

• requires channel protein or carrier protein to assist with transport

primary active transport

• transports substance(s) from lower concentration to higher concentration (against gradient)

• requires energy input

• requires protein in lipid bilayer

• breaks ATP into ADP and Pi to get energy

• all molecules in primary active transport move from low to high

secondary active transport

• 1 substance transported from lower concentration to higher concentration

• requires energy input - comes from coupling to another molecule moving with its gradient

• driven by movement of protons, which creates electrochemical gradient

• requires protein in lipid bilayer

• 1 molecule moves against gradient, other moves with gradient

metabolism

all the reactions that convert molecules into other molecules and transfer energy in living organisms

catabolism

set of reactions that break big molecules into smaller ones and release free energy + produce ATP

anabolism

set of reactions that synthesize big molecules and require an input of free energy

kinetic energy

energy of motion

potential energy

stored energy that is released by a change in an object’s structure or position

first law of thermodynamics

• aka law of conservation of energy

• energy cannot be created nor destroyed, but it can change forms

second law of thermodynamics

the amount of entropy in the universe is always increasing

free energy

• ΔG

• the amount of energy available to do work

enthalpy

• ΔH

• potential energy/bond energy

entropy

• ΔS

• disorder

exergonic

• ΔG is negative

• reaction that releases free energy

endergonic

• ΔG is positive

• reaction that requires input of free energy

Explain why endergonic reactions would be coupled to exergonic reactions.

Endergonic reactions require an input of free energy, and they need to get that energy from somewhere. Since exergonic reactions release free energy, they can couple with endergonic reactions and when the free energy is released, it can be used to power the endergonic reactions.

substrate

• reactant in a catalyzed reaction

• substance that binds to the active site of an enzyme

active site

area on the enzyme that the substrate binds to

activation energy

energy required to reach the transition state

transition state

• short period of time where bonds in reactants break and bonds in products are formed

• highly unstable

• lots of free energy

reaction rate

how quickly reactants are converted into products

How do enzymes alter the rate of chemical reactions?

Enzymes lower the activation energy of enzymes needed to begin a reaction, which increases the rate of reaction.

competitive inhibition

inhibitor competes with substrate to bind to active site

noncompetitive inhibition

inhibitor binds to allosteric site, changing the conformation of the enzyme so that the substrate can no longer bind to the active site

activator

increases enzyme activity

inhibitor

decreases enzyme activity

Is a reaction with positive ΔH and positive ΔS exergonic or endergonic?

need more information

Is a reaction with positive ΔH and negative ΔS exergonic or endergonic?

endergonic

Is a reaction with negative ΔH and positive ΔS exergonic or endergonic?

exergonic

Is a reaction with negative ΔH and negative ΔS exergonic or endergonic?

need more information