Cell & Molecular Biology

Ionic Bond

Complete transfer of electrons from one atom to another; exists between ions (charged atoms or molecules)

Covalent Bond

Electrons are shared between atoms with similar electronegativities; can be single, double, or triple bonds

Nonpolar Covalent Bond

Equal sharing of electrons between atoms with highly similar electronegativity

Polar Covalent Bond

Unequal sharing of electrons between atoms with slightly different electronegativity; forms a dipole

Hydrogen Bond

Weak bond between molecules where hydrogen is covalently bonded to F, O, or N and is attracted to another F, O, or N atom

Van der Waals Interactions

Weak, temporary attraction between atoms or molecules in close proximity due to transient, uneven distribution of electrons

Dipole

Differences in charge between two parts of a molecule

Electronegativity

The ability of an atom to attract shared electrons within a bond

Water's High Heat Capacity

Amount of heat needed to raise the temperature of water is high, making water very temperature stable

Why ice floats

Water is denser as a liquid than as a solid because H-bonds in ice form a rigid crystal structure that keeps molecules farther apart

Cohesion

Attraction between like molecules (e.g., H2O molecules); produces high surface tension in water

Adhesion

Attraction between unlike substances (e.g., water and non-water substances)

Capillary Action

Ability of liquid to flow without external forces (e.g., against gravity); explained by adhesion and cohesion together

Hydration Shell

Water dipoles interact with opposite charges in polar or ionic molecules, surrounding them

Hydrophobic

Nonpolar substances that lack permanent dipoles or charges, are not attracted by water, and do not dissolve easily

Fat-Soluble Vitamins

Vitamins A, D, E, K; excess deposited in body fat; overconsumption can lead to toxicity

Water-Soluble Vitamins

Vitamins B and C; excess not stored and are excreted in urine

Vitamin A

Visual pigment and epithelial maintenance

Vitamin D

Regulates calcium levels by promoting absorption from the intestine; synthesized when UV light strikes the skin

Vitamin E

Antioxidant that neutralizes free radicals

Vitamin K

Important for blood clotting

Vitamin B

Coenzymes or precursors to coenzymes; there are 8 different B-group vitamins

Vitamin C

Important for collagen synthesis; deficiency leads to scurvy

Dehydration Synthesis

Process by which monomers combine to form polymers, producing an H2O molecule

Hydrolysis

Process by which an H2O molecule is used to break polymer linkages

Monosaccharides

Single sugar molecule (e.g., glucose, fructose, galactose)

Disaccharides

Two monosaccharides joined by a glycosidic linkage (e.g., sucrose, lactose, maltose)

Polysaccharides

Series of connected monosaccharides that form long chains

Alpha Glycosidic Bond

Bond in α-glucose polymers; can be cleaved by humans

Beta Glycosidic Bond

Bond in β-glucose polymers; humans cannot cleave these linkages

Starch

α-glucose polymer with branched structure; stores energy in plants

Glycogen

α-glucose polymer with branched structure; stores energy in animals

Cellulose

β-glucose polymer with no branching; structural molecule in plant cell walls

Chitin

β-glucose polymer; structural molecule in fungi cell walls and arthropod exoskeletons; contains nitrogen atoms

Triglycerides

Three nonpolar fatty acid chains attached to a glycerol backbone

Saturated Fatty Acids

No double bonds; forms straight chains; stacks densely and forms fat plaques (less healthy)

Unsaturated Fatty Acids

Contains double bonds; branched structure; stacks loosely and does not form fat plaques (more healthy)

Phospholipid

Two fatty acids and a phosphate group attached to a glycerol backbone; amphipathic with polar head and nonpolar tail

Amphipathic

Having both hydrophilic and hydrophobic properties

Phospholipid Bilayer

Two layers of phospholipids; polar heads face aqueous environments while fatty acid tails face each other

Steroids

Four joined hydrocarbon rings; form steroid hormones, cholesterol, vitamin D, and bile acids

Porphyrins

4 joined pyrrole rings with a central metal atom; examples: chlorophyll (central Mg) and hemoglobin (central Fe)

Cholesterol function in membranes

Prevents excess membrane fluidity and rigidity; added to membranes based on temperature

Cold temperature membrane adaptation

Cells add cholesterol and unsaturated fatty acids to prevent excess membrane stiffness

Hot temperature membrane adaptation

Cells add cholesterol and saturated fatty acids to prevent excess membrane fluidity

Primary Structure of Protein

Linear sequence of amino acids connected by peptide bonds; determined by mRNA codon sequence

Secondary Structure of Protein

3D shape resulting from hydrogen bonding between amino and carboxyl groups; includes alpha helix and beta sheet

Tertiary Structure of Protein

3D structure due to interactions between amino acid R groups (H-bonds, ionic bonds, hydrophobic effect, disulfide bonds, Van der Waals)

Quaternary Structure of Protein

3D structure arising from multiple protein subunits joining together

Protein Denaturation

Loss of 3D structure (protein retains only primary structure); leads to loss of function

Denaturation Agents

Temperature, pH, change in salt concentration, UV light, and chemicals

Nucleotide

Nitrogen base (A, C, G, T, U) + five carbon sugar (deoxyribose in DNA, ribose in RNA) + phosphate group

Purines

Nucleotides with double ring nitrogen bases: adenine and guanine

Pyrimidines

Nucleotides with single ring nitrogen bases: cytosine, uracil, and thymine (mnemonic: CUT the PYE)

DNA Structure

Double-stranded polymer containing deoxyribose sugar; two strands intertwined in a double helix

Phosphodiester Bond

Covalent linkage connecting nucleotides on the same DNA/RNA strand (5' to 3' direction)

DNA Antiparallel

Each DNA strand runs 5' to 3' in opposite directions

DNA Complementarity

Nitrogen bases on one strand bind to their complementary base on the opposing strand (A-T, G-C)

AT Base Pair

Adenine binds to Thymine with 2 hydrogen bonds

GC Base Pair

Guanine binds to Cytosine with 3 hydrogen bonds

Chargaff's Rule

Number of purines always equals number of pyrimidines (A + G = T + C; A = T and C = G)

RNA Structure

Usually single-stranded polymer of nucleotides containing ribose sugar; has uracil instead of thymine

Ribose vs Deoxyribose

Ribose has an extra OH group compared to deoxyribose, making RNA more reactive than DNA

Cell Theory

1) All organisms are composed of cells 2) Cell is basic unit of structure 3) All cells come from pre-existing cells 4) Organism activity depends on combined cell activity 5) Cells have functional metabolism 6) Cells contain hereditary genetic information 7) Cells of similar species have same basic chemical composition

Prokaryotes

Less complex cells; no nucleus or membrane-bound organelles

Eukaryotes

More complex cells; have nucleus and membrane-bound organelles

Plasma Membrane Structure

Phospholipid bilayer with fatty acid tails pointing inward and phosphate heads facing aqueous environments

Selective Permeability

Only certain substances can cross the membrane without assistance from transport proteins

Small Nonpolar Molecules Permeability

Can cross membrane on their own (e.g., steroids, CO2, O2, N2)

Small Uncharged Polar Molecules Permeability

Can cross membrane on their own (e.g., H2O, glycerol, urea, ethanol)

Large Uncharged Polar Molecules Permeability

Unable to cross membrane on their own (e.g., glucose, sucrose)

Ion Permeability

Unable to cross membrane on their own (e.g., Na+, H+, Ca2+)

Fluid Mosaic Model

Cell membrane is fluid (phospholipids move freely) and mosaic (different components like proteins are embedded)

Nucleus

Contains the cell's DNA; controls gene expression

Nuclear Envelope

Double membrane with pores allowing molecules to enter and exit the nucleus

Nuclear Lamina

Protein network that maintains the shape of the nucleus

Nucleolus

Region inside nucleus where ribosomal RNA (rRNA) is made

Chromatin

Condensed form of DNA wrapped around histone proteins

Nucleosome

A bundle of 8 histones with DNA coiled around them

Chromosome

Tightly condensed chromatin visible when cell is ready to divide

Ribosomes

Non-membrane-bound organelles responsible for protein synthesis (translation); composed of 2 subunits with rRNA and protein

Free Floating Ribosomes

Make proteins that function inside the cell

Bound Ribosomes

Attached to rough ER; make proteins exported out of the cell

Rough ER

Synthesizes and modifies proteins before export; studded with ribosomes; capable of post-translational modifications

Smooth ER

Synthesizes lipids and steroid hormones; no ribosomes; also breaks down toxins in liver cells

Sarcoplasmic Reticulum

Specialized smooth ER in muscle cells that stores and releases Ca2+ ions

Golgi Apparatus

Series of flattened membrane sacs that sort, modify, and transport proteins after synthesis; produces lysosomes

Golgi Directionality

Cis end accepts incoming vesicles; trans end exports vesicles

Post-translational Modification Organelles

Rough ER and Golgi Apparatus

Lysosomes

Digestive enzyme-containing membrane-bound vesicles; involved in apoptosis, autophagy, nutrient breakdown, and pathogen destruction

Peroxisomes

Break down toxic substances and fatty acids; produce and breakdown H2O2 using catalase

Central Vacuole

Large vacuole in plants for nutrient and water storage; exerts turgor pressure when filled

Contractile Vacuoles

Collect and pump excess water out of cells to prevent bursting; found in protists in hypotonic environments

Cytoskeleton

Network of tubules and filaments; maintains cell shape, enables movement, and anchors membrane proteins

Microfilaments

Composed of two intertwined strands of actin; function in cell motility (smallest cytoskeleton component)

Intermediate Filaments

Composed of intertwined coiled proteins (e.g., keratin); provide support to maintain cell shape

Microtubules

Hollow tubes made of tubulin polymers; provide support and motility for cellular activities (largest cytoskeleton component)

Flagella

Whip-like extensions from cells used for movement

Cilia

Short, hair-like extensions from cells used for movement or sweeping substances

Centrosome

Two perpendicularly arranged centrioles used in formation of spindle fibers during cell division