lab practical (chat)

Enzyme

A biological catalyst that accelerates chemical reactions without being consumed in the process.

Primary macromolecule composing enzymes

Proteins.

Substrate

The specific reactant molecule upon which an enzyme acts.

Active site

The specific region on an enzyme where the substrate binds and catalysis takes place.

Activation energy

The initial input of energy required to start a chemical reaction.

Effect of enzymes on activation energy

Enzymes lower the activation energy required for a reaction to proceed.

Products (chemical reactions)

The chemical substances formed as a result of a reaction.

Denaturation of an enzyme

A structural alteration in an enzyme's three-dimensional shape that impairs or destroys its catalytic activity.

Optimal conditions for an enzyme

The specific environmental factors, such as temperature and pH, at which an enzyme exhibits maximum catalytic efficiency.

Effect of excessively low temperature on enzyme activity

Reaction rates decrease due to reduced molecular kinetic energy and fewer substrate collisions.

Effect of extreme high temperature on enzymes

Thermal agitation disrupts bonds stabilizing tertiary structure, leading to irreversible denaturation.

Effect of extreme pH on an enzyme

Alters the ionic charges and hydrogen bonds of amino acid residues, modifying active site geometry and reducing activity.

Method to determine optimal temperature on an enzyme activity graph

Locate the peak of the rate curve and read the corresponding value on the temperature axis.

Method to determine optimal pH on an enzyme activity graph

Locate the peak of the rate curve and read the corresponding value on the pH axis.

Catalase

An antioxidant enzyme that catalyzes the decomposition of hydrogen peroxide into water and oxygen gas.

Substrate of catalase

Hydrogen peroxide ($H_2O_2$).

Balanced equation for the catalase reaction

$$2H_2O_2 \rightarrow 2H_2O + O_2$$

Products of the catalase reaction

Water ($H_2O$) and oxygen gas ($O_2$).

Indication of bubbling in the catalase reaction

Production and release of oxygen gas ($O_2$).

Cellular importance of catalase

Prevents oxidative cell damage by breaking down toxic hydrogen peroxide.

Comparison of catalase activity: beef liver vs. potato

Beef liver typically exhibits significantly higher catalase activity and reaction rates compared to potato tissue.

Reason beef liver exhibits strong catalase activity

Liver tissue functions heavily in metabolic detoxification and possesses a high density of peroxisomes rich in catalase.

Presence of catalase in plant tissues like potatoes

Yes, plant tissues contain catalase to decompose reactive oxygen species.

Experimental significance of increased bubbling in a catalase assay

Indicates a higher volume of oxygen gas produced, reflecting increased enzyme reaction velocity.

Photosynthesis

The anabolic pathway by which photoautotrophs convert light energy into chemical energy stored in glucose using carbon dioxide and water.

Reactants of photosynthesis

Carbon dioxide ($CO_2$), water ($H_2O$), and light energy.

Products of photosynthesis

Glucose ($C_6H_{12}O_6$) and oxygen gas ($O_2$).

Balanced equation for photosynthesis

$$6CO_2 + 6H_2O + \text{light energy} \rightarrow C_6H_{12}O_6 + 6O_2$$

Chemical formula for glucose

$$C_6H_{12}O_6$$

Gaseous reactant absorbed by plants for photosynthesis

Carbon dioxide ($CO_2$).

Gaseous by-product released during photosynthesis

Oxygen ($O_2$).

Energy transformation occurring in photosynthesis

Radiant (light) energy is transformed into chemical potential energy stored in covalent bonds of organic molecules.

Paper chromatography

An analytical separation technique that separates solutes based on their relative affinities for a stationary phase versus a mobile solvent.

Purpose of paper chromatography in spinach pigment analysis

To separate and resolve the individual photosynthetic pigments present in spinach leaves.

Mechanism of solvent migration in paper chromatography

Capillary action draws the mobile solvent upward through the cellulose fibers of the paper.

Primary factors causing differential pigment migration in chromatography

Variations in pigment solubility in the mobile phase versus adsorption/affinity to the stationary cellulose phase.

Migration behavior of pigments with high solvent solubility

They travel farther up the chromatography paper toward the solvent front.

Migration behavior of pigments with strong paper affinity

They interact strongly with cellulose and remain closer to the origin baseline.

Initial placement of the pigment spot relative to the solvent line

Positioned strictly above the solvent level so pigments do not dissolve directly into the solvent reservoir.

Four primary photosynthetic pigments separated from spinach

Carotene, xanthophyll, chlorophyll a, and chlorophyll b.

Observed color of carotene

Orange.

Observed color of xanthophyll

Yellow.

Observed color of chlorophyll a

Blue-green.

Observed color of chlorophyll b

Yellow-green.

Order of spinach pigments on a chromatogram from top to bottom

Carotene, xanthophyll, chlorophyll a, chlorophyll b.

Spinach pigment migrating the greatest distance from origin

Carotene.

Spinach pigment remaining closest to the origin line

Chlorophyll b.

Meaning of Rf in chromatography

Retention factor (or retardation factor).

Formula for calculating Rf

$$R_f = \frac{\text{distance traveled by pigment}}{\text{distance traveled by solvent front}}$$

Measurement procedure for pigment distance in an Rf calculation

Measure from the baseline origin to the center of the resolved pigment band.

Measurement procedure for solvent distance in an Rf calculation

Measure from the baseline origin to the solvent front line.

Units for Rf values

Unitless (dimensionless ratio).

Standard mathematical range for Rf values

Between $0$ and $1$.

Rf calculation: pigment travels $3\,\text{cm}$, solvent travels $6\,\text{cm}$

$$0.50$$

Rf calculation: pigment travels $4\,\text{cm}$, solvent travels $8\,\text{cm}$

$$0.50$$

Rf calculation: pigment travels $6\,\text{cm}$, solvent travels $8\,\text{cm}$

$$0.75$$

Rf calculation: pigment travels $2\,\text{cm}$, solvent travels $10\,\text{cm}$

$$0.20$$

Rf calculation: pigment travels $5\,\text{cm}$, solvent travels $10\,\text{cm}$

$$0.50$$

Acid formed when carbon dioxide dissolves in water

Carbonic acid ($H_2CO_3$).

Reversible equation for carbonic acid synthesis

$$CO_2 + H_2O \rightleftharpoons H_2CO_3$$

Effect of carbonic acid formation on solution pH

Increases hydronium ion concentration, causing pH to decrease (more acidic).

pH

A logarithmic measure of the concentration of free hydrogen/hydronium ions in an aqueous solution.

Chemical condition indicated by pH < 7

Acidic solution.

Chemical condition indicated by pH = 7

Neutral solution.

Chemical condition indicated by pH > 7

Basic (alkaline) solution.

Effect of increasing dissolved CO2 on aquatic pH

Decreases pH due to the shift toward carbonic acid dissociation.

Effect of photosynthetic CO2 consumption on aquatic pH

Increases pH because reduced dissolved carbon dioxide decreases carbonic acid levels.

Function of a CO2 indicator in algae bead experiments

Tracks changes in solution pH corresponding to the uptake or release of dissolved carbon dioxide.

Color of the CO2 indicator under acidic conditions

Yellow.

Color of the CO2 indicator under alkaline conditions

Blue or purple.

Reason for rising pH in illuminated algae bead cultures

Photosynthetic consumption of $CO_2$ reduces carbonic acid concentration, driving pH upward.

Reason for declining pH in darkened algae bead cultures

Absence of photosynthesis combined with ongoing cellular respiration produces $CO_2$, forming carbonic acid and lowering pH.

Two major biochemical stages of photosynthesis

The light-dependent reactions and the Calvin cycle (light-independent reactions).

Subcellular site of the light-dependent reactions

Thylakoid membranes within chloroplasts.

Requirement of light in light-dependent reactions

Directly required to excite electrons within photosystems.

Energy carriers synthesized during light reactions for the Calvin cycle

$\text{ATP}$ and $\text{NADPH}$.

Photolysis of water in light-dependent reactions

Water molecules are oxidized and split, yielding electrons, protons, and byproduct oxygen gas.

Subcellular site of the Calvin cycle

Stroma of chloroplasts.

Direct light requirement of the Calvin cycle

Does not directly require photons, but relies on chemical intermediates ($\text{ATP}$ and $\text{NADPH}$) produced by light reactions.

Primary role of the Calvin cycle

Fixes inorganic carbon dioxide into organic triose phosphate sugars using $\text{ATP}$ and $\text{NADPH}$.

Location mnemonic for photosynthetic stages

Light reactions = Thylakoids; Calvin cycle = Stroma.

Validity of the term 'dark reactions' implying night-only operation

Misleading; the cycle does not require darkness, but depends upon products continuously generated by light reactions.

Cell cycle

The regulated sequence of growth, DNA synthesis, and nuclear and cytoplasmic division in a eukaryotic cell.

Major events of the G1 phase

Cellular growth, metabolic activity, and synthesis of proteins and organelles.

Major events of the S phase

Replication of nuclear DNA and duplication of centrosomes.

Major events of the G2 phase

Final cellular growth, protein synthesis, and assembly of structures needed for mitosis.

Major events of the M phase

Nuclear division (mitosis) followed by cytoplasmic separation (cytokinesis).

Three constituent stages of interphase

$G_1$, S, and $G_2$ phases.

Activity state of cells during interphase

Highly active; the cell actively metabolizes, transcribes genes, grows, and replicates its genome.

Chromosome

A compact, organized structure composed of a single double-stranded DNA molecule associated with histone proteins.

Sister chromatids

Identical duplicates of a chromosome produced during DNA replication, held together at the centromere.

Centromere

The specialized constricted chromosomal locus that tethers sister chromatids and serves as the assembly site for kinetochores.

Spindle fibers

Cytoskeletal microtubule polymers that coordinate chromosomal alignment and segregation during mitosis and meiosis.

Cytokinesis

The physical division of the parental cytoplasm yielding two daughter cells.

Correct sequence of mitotic stages

Prophase, metaphase, anaphase, telophase.

Mnemonic for the four stages of mitosis

Please Make Another Two (PMAT): Prophase, Metaphase, Anaphase, Telophase.

Key cellular hallmarks of prophase

Chromatin condenses into distinct chromosomes, the mitotic spindle nucleates, and the nucleolus and nuclear envelope disassemble.

Microscopic recognition of prophase

Dark condensed chromatin strands appear within the nuclear area without equatorial alignment.

Key cellular hallmarks of metaphase

Chromosomes align along the equatorial metaphase plate perpendicular to spindle poles.

Microscopic recognition of metaphase

Chromosomes are aligned in a distinct single linear band across the center of the cell.