Cell Biology Study Guide Essay Sample

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List the key commonalties and differences between prokaryotic and eukaryotic cells. Prokaryotic – no organelles; no nucleus; bacteria and Achaea; spherical, rodlike/corkscrew-shaped; cell wall; Eukaryotic – has nucleus; has organelles

Commonalities – contain DNA that stores genetic information

What is the main component of cellular membranes? What function(s) do membranes serve in cells? Made of phospholipids; defines volume of cell; isolates the cell from environment; Motility/Morphology; Signal recognition and transduction; transport of small molecules and some ions

Summarize the key structures and functions of the following organelles: nucleus-double membrane (nuclear envelope); outer membrane continuous with the ER; DNA synthesis and repair; transcription; ribosome synthesis endoplasmic reticulum (rough and smooth)-largest amount of membrane; RER-studded with ribosomes; synthesis of membrane bound and exported proteins; SER-synthesis of lipids and steroid hormones; calcium signaling; detoxification reactions

Golgi apparatus-series of membrane stacks; processing and sorting of proteins to cellular compartments including export Lysosomes-single membrane; interior is pH 5; cellular digestion: autophagy Peroxisomes-small and spherical; long chain fatty acid oxidation; lipid oxidation; O2 and H2O2 based reactions Mitochondria-ETC; generation of ATP; oxidation of pyruvate, fatty acids, amino acids; apoptosis; contain own DNA and reproduce dividing in two Chloroplasts – capture energy from sunlight; found in plants and algae;

Know size ranges for the cell and its components. Be able to convert between units of measure. 1m=103 mm=106µm =109 nm

What are the functions of the cytoskeleton? Name the different types of cytoskeletal fibers. Cell motility, cell shape, cellular organization; microtubules, actin, intermediate filaments

What is meant by the term ‘model organism’? List the common model organisms (described in book but not in class). Model organism – an organism selected for intensive study as a representative of a large group of species. Examples are the mouse (representing mammals), the yeast Saccharomyces cerevisiae (representing a unicellular eukaryote), and E coli (representing bacteria), the fruit fly Drosophilia melanogaster, and Arabidopsis thaliana (representing plants)

Chapter 2

Which 4 elements make up the majority of atomic composition found in living things? Hydrogen, Carbon, Oxygen, Nitrogen

Describe the 3 main subatomic particles (define their role in atomic structure). Protons – positively charged, determines atomic number; Electrons – negatively charged; Neutrons – neutral, uncharged, same mass as protons, structural stability of the nucleus

Explain covalent and ionic bonding. Give an example of each. Covalent bond – molecules formed when two atoms share a pair of electrons; e.g. H2; Ionic bond – transfer of electrons, electrons are donated by one atom to another, electrostatic attraction (an attractive force that occurs between oppositely charge atoms; e.g. NaCl

Explain the concept of polarity – use water as an example. The positive charge is concentrated toward one end of the molecule (the positive pole) and the negative charge is concentrated toward the other end (the negative pole)

Explain the terms hydrophilic and hydrophobic. Be able to classify molecules as one, the other, or both (fatty acids/lipids), based on their structures. Hydrophilic – water loving, dissolve in water, contain positive or negative charges (ions): sugars, DNA, RNA, and majority of proteins, carboxyl head group Hydrophobic – water fearing; uncharged and form few or no hydrogen bonds, do not dissolve in water: hydrocarbons

How many covalent bonds do the atoms carbon, hydrogen, oxygen, and nitrogen usually form? Carbon – 4; hydrogen – 1; oxygen – 2; nitrogen – 3

Be able to identify the following chemical functional groups: hydroxyl group -OH, carboxyl group -COOH, methyl group –CH3, carbonyl group –C=O, amino group –NH2 and phosphate group –PO32-.

What types of larger molecules are made from sugars (monosaccharides)? What functions do monosaccharides and their derivatives serve in cells? Carbohydrates=>oligosaccharides=>polysaccarharides Functions: production and storage of energy; cell walls (cellulose, chitin);extracellular matrix; DNA/RNA; linked to proteins

Describe the basic structure of a fatty acid. How are phospholipids constructed from fatty acids? List some functions of fatty acid. Two chemically distinct regions: long hydrocarbon chain and carboxyl head group; Saturated – no double bonds, solid margarine; Unsaturated – one or more double bonds, liquid/soft margarine (oil) Phospholipid – the glycerol is joined to two fatty acid chains and phosphate group, which is linked to a hydrophilic head Function: production and storage of energy, cell membrane, cell signaling

Draw and describe the basic structure of an amino acid. What determines the chemical properties of an amino acid? Be able to classify the 20 amino acids into the 4 families specified in the book (acidic, basic, uncharged polar, nonpolar). Structure: carboxylic acid group (COO-) and amino group (NH3+), both linked to same carbon atom; Side chains confer functionality

Acidic: Asp, Glu

Basic: Arg, Lys, His
Uncharged Polar: Asn, Gln, Ser, Thr, Tyr
Nonpolar: Ala, Gly, Val, Leu, Ile, Pro, Phe, Met, Trp, Cys

What are the components that make up the structure of a nucleotide. What are the 2 differences between the ribonucleotides and deoxyribonucleotides? What is the difference between a nucleotide and nucleoside? Nucleotide – nitrogen ring, sugar, phosphate group Ribonucleotides – nucleotide containing ribose; A, G, U, T Deoxyribonucleotides – nucleotide containing deoxyribose; A, G, C, T Nucleoside = nucleotide – phosphate

What are some functions of nucleotides in cells? DNA, RNA, Carriers of chemical energy (ATP), signaling molecules, coenzymes (ATP, Coenzyme A, NAD+, FAD)

What common reaction is used in the synthesis of larger biomolecules? Know the 4 main building blocks and the larger units that are made inside the cell. Condensation; Sugars=>polysaccharides; fatty acids=>fats, lipids, membranes; amino acids=>proteins; nuclotides=>nucleic acids

List and explain the 4 types of noncovalent weak chemical interactions occurring in cells. How do they determine the conformation of a macromolecule? Conformations are highly constrained because of weaker noncovalent bonds that form between different parts of the molecule; determined by the linear sequence of monomers in its chain Electrostatic/ionic attractions – weak in water; transfer of electrons Hydrogen bonds – bond when a hydrogen (+) is sandwiched between two electron attracting ions (-); holds the two strands of DNA double helix together; e.g. amino acids in polypeptide chains Van der Waals attractions – a form of electrical attraction caused by fluctuating electric charges that arise whenever two atoms come within a very short distance of each other Hydrophobic interaction – forces phospholipid molecules together in cell membranes, gives most proteins a globular shape; to minimize interaction with water or hydrophilic environment

Order from strongest to weakest: covalent=>ionic=>hydrogen=>van der Waals

Chapter 3

State the 2nd law of thermodynamics and its relevance to the cell. In any system, the degree of disorder (entropy) will increase over time. The increased order maintained within the cell generates increased disorder (heat) that is released out of the cell

Explain the terms metabolism, catabolism, and anabolism. Metabolism – the sum total of all the chemical reactions it needs to carry out to survive, grow, and reproduce Catabolism – break down foodstuffs into smaller molecules, thereby generating both a useful form of energy for the cell and some of the small molecules that the cell needs as building blocks Anabolism – use the energy harnessed by catabolism to drive the synthesis of the many molecules that form the cell

Contrast energetically favorable and unfavorable reactions with regard to:
•change in free energy (G)
•absorption/release of energy
Energetically favorable – create disorder by decreasing the free energy of the system to which they belong; negative ΔG; spontaneous; release of free energy into environment

Energetically unfavorable – by themselves created order in the universe; positive ΔG; nonspontaneous; can only take place if coupled with a negative ΔG so large that the net ΔG of the entire reaction is negative; gains free energy into system

Define change in free energy based on enthalpy and entropy. ΔG = ΔH – T ΔS, where ΔH is change in number of bond formed and/or broken and ΔS is the change in randomness

What two things does ∆G (that is, GB − GA) tell you about the reaction A → B? Explain what it means if 1) GA is greater GB, 2) if GA is less than GB, and 3) if GA is equal to GB. 1) ΔG is negative, spontaneous, energetically favorable, ratio of A B increases; 2) ΔG is positive, nonspontaneous, energetically unfavorable; 3) the reaction is at equilibrium A↔B

Based on the equation ΔG = ΔG0 + 0.616 ln ([B] / [A]) from lecture, what 2 factors determine whether a given reaction will occur (i.e., what determines G)? Substrates and products What is the difference between ∆G and ∆G°, and what does their correlation depend on? ΔG is the free energy IN THE CELL; ΔG° is the standard free energy IN THE TEST TUBE; correlation depends on the concentration of substrate and product in the CELL

Give the equation for the equilibrium constant (Keq) for a reaction A → B. What does this value tell you about ΔG0? (This answer may be expressed mathematically.) K = [B] / [A] ΔG = -1.42 log10K

K = 10-ΔG°/1.42

What is the name of the energy barrier that must be overcome for a chemical reaction to occur? Explain how an enzyme acts as a catalyst to overcome the barrier. Activation energy; enzymes lower the activation energy for catalyzed reaction YX (reactantproduct); it DECREASES the ACTIVATION ENERGY by bringing the substrate into a favorable conformation with the enzyme; can also undergo energetic changes that provide some of the energy needed by the reaction

What is the active site of an enzyme and what does it do? In what way does an enzyme affect the equilibrium of a chemical reaction? Active site – a specialized region of an enzyme surface to which a substrate molecule binds before it undergoes a catalyzed reaction

Describe the concept of coupling whereby unfavorable reactions can be accomplished in cells; explain how the ‘favorability’ of each mechanism can be mathematically determined. Coupling – an energetically favorable reaction is used to drive an energetically unfavorable one that produces an activated carrier molecule or some other useful molecule; require enzymes

Explain what happens in a typical oxidation reaction in the cell using NAD+ (or NADP+) as an example. Oxidation – removal of electrons (lose a H atom) NAD+ and NADP+ are utilized as electron acceptors (electron carriers); picks up “packet of energy” in form of two high-energy electrons plus a proton (H+) becoming NADH and NADPH; the substrate is oxidized and the NAD+ and NADP+ is reduced. The hydride ion carried by NADPH is given up readily in a subsequent oxidation-reduction reaction, because the ring can achieve a more stable arrangement of electrons without it; regenerates NADP+, the NADPH becomes oxidized and the substrate becomes reduced—thus completing the NADPH cycle.

Summarize the cellular roles of NAD+, FAD, and NADP+.
Plenty of NAD+ to act as oxidizing agents and plenty of NADPH to act as reducing agents; NAD+ required role for catabolism; NADPH required role for anabolism

NADH and FADH2 transfer electrons to the electron transport chain enzymes in the mitochondria

Summarize how ATP can be used to drive an unfavorable reaction by phosphoryl transfer potential. The energetically favorable reaction of ATP hydrolysis is COUPLED to many otherwise unfavorable reactions through which other molecules are synthesized. Such hydrolysis reactions often involve the transfer of the terminal phosphate in ATP to another molecule.

ATP gives up energy packet in energetically favorable hydrolysis to ADP and inorganic phosphate. The regenerated ADP is then available to be used for another round of the phosphorylation reaction that forms ATP, creating an ATP cycle in the cell.

Explain the function of coenzymes, using coenzyme A as an example. Coenzymes are small molecules which bring unique chemical functionality to certain enzyme reactions. Coenzyme A can carry an acetyl group in a readily transferable linkage; makes an activated molecule called acetyl CoA and used to add two-carbon units in the biosynthesis of the hydrocarbon tails of fatty acids; carries 2-24 carbon units; terminal thioester group is a reactive site

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