TEAS Life Science Practice Review

• Definition of a Macromolecule: A macromolecule is defined as a very large molecule consisting of repeating structural units called monomers, which are covalently bonded together to form long chains or branched structures known as polymers. These compounds are essential for life as they serve various critical functions in biological systems.

• Specific Examples of Molecules:
    - DNA (Deoxyribonucleic Acid): Composed of long chains of nucleotides, each comprising a sugar, a phosphate group, and a nitrogenous base. The sequence of these nucleotide bases (represented by the letters T, A, C, and G) encodes genetic information vital for the growth and reproduction of organisms.   - RNA (Ribonucleic Acid): Similar to DNA, RNA is made up of nucleotides (A, C, U, G) but typically exists in a single-stranded form. RNA plays various roles, including serving as a messenger carrying instructions from DNA for controlling the synthesis of proteins.   - Protein: Proteins are macromolecules composed of one or more long chains of amino acids (monomers) linked by peptide bonds. They perform a vast array of functions within organisms, including catalyzing metabolic reactions, replicating DNA, responding to stimuli, and transporting molecules.   - Glucose: A simple sugar (monosaccharide) and a fundamental source of energy for cells. While glucose itself is not a macromolecule, it polymerizes to form larger macromolecules:     - Starch: A carbohydrate commonly found in plants, serves as a long-term energy storage molecule. It consists of linear and branched chains of glucose units.     - Glycogen: The storage form of glucose in animals, it is highly branched and functions as a readily accessible energy reserve.     - Cellulose: A structural carbohydrate that constitutes the cell wall in plants, providing rigidity and support. It consists of linear chains of glucose that are hydrogen-bonded to each other, making it resistant to enzymatic breakdown.

Biological Nomenclature and Enzyme Clues

• Chemical Suffixes: In biological nomenclature, the suffix “-ase” indicates that the substance is an enzyme, which acts as a biological catalyst.

• Suffix/Substrate Relationship: The prefix of an enzyme's name often hints at the substrate it acts upon:   - Lactase: An enzyme that digests lactose, a sugar found in milk.   - Sucrase: Enzyme that breaks down sucrose, also known as table sugar.   - Amylase: Enzyme that digests amylose, a component of starch.   - Classification: Lactose, sucrose, and amylose are all carbohydrates, thus the enzymes mentioned facilitate carbohydrate digestion.

Metabolism: Anabolism and Catabolism

• Metabolism Definition: Metabolism encompasses the total of all chemical reactions that occur within an organism to maintain life. It is fundamentally divided into two interconnected processes:   - Anabolism: The biosynthetic phase of metabolism that builds larger molecules from smaller ones, which typically requires energy input (e.g., ATP). This includes processes such as protein synthesis and DNA replication.
    - Catabolism: The degradative phase of metabolism where larger molecules are broken down into smaller units releasing energy. For instance, during protein digestion, amino acids can be degraded to form molecules like urea and carbon dioxide ($CO_2$) along with energy in the form of ATP, reflecting a classic example of catabolic reactions.

Enzyme Function and Denaturation

• Enzymes as Catalysts: Enzymes are specialized protein molecules that increase the rate of chemical reactions by lowering the activation energy required for them to proceed. Their specific shape is crucial for their function.

• Chymosin Example: Chymosin serves in cheesemaking by inducing the coagulation of milk. It catalyzes the cleavage of peptide bonds in kappa-casein protein, facilitating curd formation essential for cheese texture.

• 3D Structure: Enzymes possess complex tertiary or quaternary structures that dictate their function. The specific folding patterns create active sites that precisely fit their substrate molecules, enabling catalytic efficiency.

• Optimal Conditions: Each enzyme operates optimally under specific environmental conditions:   - Optimal pH: For many enzymes, maximum activity occurs around $pH eq 6$, as extreme pH values can lead to denaturation.   - Optimal Temperature: Enzymatic reactions typically peak at temperatures around $37^{ au} ext{C}$. Higher temperatures can render enzymes inactive through denaturation.

• Denaturation:
    - Definition: Denaturation refers to the alteration of an enzyme's three-dimensional structure due to external stresses, resulting in loss of functionality.   - Causes: Conditions like extreme pH or temperature may destabilize the enzyme's structure:     - pH Fluctuations: Deviations from the optimal pH disrupt the ionization of enzyme active sites.     - Temperature Variations: High temperatures can disrupt hydrogen and ionic bonds crucial for maintaining structure. Conversely, low temperatures typically slow down reaction rates without causing denaturation.

Cellular Structures and Components

• Phospholipids: Essential for cell membrane structure.   - Structure: Comprising a glycerol backbone, a phosphate group, and two hydrophobic fatty acid tails, phospholipids spontaneously form bilayers in aqueous environments, serving as fundamental boundaries for cells.   - Chemical Nature: The amphipathic nature—having both hydrophilic (water-attracting) and hydrophobic (water-repelling) components—allows for the fluidity and functionality of the cell membrane.

• Nucleotides: The building blocks of nucleic acids.   - Three Components:
      1. Phosphate Group: Contributes to the backbone structure and enables linkage with other nucleotides.     2. Sugar: Can be either deoxyribose in DNA or ribose in RNA, affecting the structural properties of the nucleic acid.     3. Nitrogenous Base: The information-carrying component (e.g., Adenine, Thymine, Guanine, Cytosine in DNA; Uracil replaces Thymine in RNA).   - Naming Hints: The names highlight their components; for instance, DNA denotes Deoxyribonucleic Acid (indicating the absence of one oxygen compared to RNA).

Prokaryotes versus Eukaryotes

• Prokaryotes:
    - Comprising primarily bacteria, these cells are characterized by their simplicity and lack of a nucleus. Their DNA is located in the nucleoid region.   - Organelle Composition: Prokaryotes lack complex organelles such as mitochondria or the endoplasmic reticulum, which are definitive features of eukaryotic cells.   - Size: Generally smaller than eukaryotic cells, often about 0.1 to 5.0 micrometers in diameter.

• Eukaryotes:
    - This category encompasses a wide variety of organisms, including plants and animals. Their cells contain membrane-bound nuclei where the genetic material is housed.
    - Organelles: Eukaryotic cells boast numerous organelles enabling compartmentalization of cellular functions, such as mitochondria for energy production and the endoplasmic reticulum for protein/lipid synthesis.

• Shared Structures: Despite their differences, both prokaryotic and eukaryotic cells share fundamental cellular components, including a cell membrane, ribosomes for protein synthesis, and cytoplasm as the cellular matrix in which these organelles reside.

Organelle Functions

• Rough Endoplasmic Reticulum (RER): Involved primarily in the synthesis of proteins directed for export out of the cell or for lysosomes.

• Smooth Endoplasmic Reticulum (SER): Associated with lipid synthesis, metabolism of carbohydrates, and detoxification of drugs and poisons.

• Golgi Apparatus: Functions as the cell’s “post office,” responsible for the modification, sorting, and packaging of proteins for secretion or delivery to other organelles.

• Lysosome: Functions as the “garbage truck” of the cell by containing digestive enzymes responsible for breaking down waste materials and cellular debris. Lysosomes are prevalent in macrophages, which utilize them to digest engulfed pathogens.

• Mitochondria: Often referred to as the powerhouse of the cell; they are responsible for energy production through the process of cellular respiration, converting biochemical energy into ATP.

• Chloroplasts: Present in plant cells, chloroplasts enable photosynthesis by capturing light energy and converting it into chemical energy stored in glucose. Their structure includes thylakoids arranged in stacks called grana, where light-dependent reactions occur.

Bioenergetics: Photosynthesis

• Definition: Photosynthesis is the biochemical process through which photoautotrophs, particularly plants and certain bacteria, synthesize their own food in the form of glucose from carbon dioxide and water, using sunlight as the energy source.

• Chemical Process: The necessity of light energy for the reaction is denoted in the chemical equation, playfully represented over the reaction arrow indicating its catalytic importance.

• General Equation: $CO_2 + H_2O ightarrow C_6H_{12}O_6 + O_2$, illustrating the conversion of inorganic materials into vital organic compounds and oxygen released as a byproduct.

Cell Differentiation and Developmental Biology

• Stem Cells: Unique cells capable of differentiating into various specialized cell types (e.g., blood, nerve, muscle), providing a potential source for regeneration and repair in organisms.

• Differentiation: The biological process by which a stem cell acquires specific structural and functional properties of a particular cell type, guided by genetic and environmental factors.

• Potency Levels:
    - Totipotent: Stem cells that can form any cell type, including those required for embryo implantation (e.g., zygote cells).   - Pluripotent: Cells capable of differentiating into nearly all cell types except those needed for placental structures (e.g., embryonic stem cells).   - Multipotent: These cells can develop into a limited number of cell types related by lineage (e.g., hematopoietic stem cells, which can become various blood cells).
    - Unipotent: Stem cells specialized in forming only one cell type (e.g., muscle stem cells).