Cell Biology Review: Cytology, Metabolism, Molecular Genetics, and Genetics

Comprehensive vocabulary flashcards covering cell theory, cytology, metabolism, enzyme kinetics, cell transport, cellular respiration, molecular genetics, protein synthesis, meiosis, and Mendelian inheritance based on the lecture notes.

Cell Theory

A fundamental biological principle stating two main tenets: 1) All living organisms are composed of cells, and 2) Every cell originates from a pre-existing cell.

Cell

The structural and functional unit of life, characterized as an open system that exchanges matter and energy with its environment and responds to environmental variations.

Principle of Emergence

The concept that at each higher level of biological organization, new properties emerge that were not present at lower levels, summarized by 'The whole is greater than the sum of its parts.'

Cytosol

The semi-liquid aqueous solution of the cytoplasm containing suspended ions, molecules, and particles, in which chemical reactions occur.

Cytoplasm

The cellular region between the nucleus and the plasma membrane, consisting of the cytosol and suspended organelles.

Prokaryote

A unicellular organism (belonging to Bacteria or Archaea) characterized by small cell size, the absence of membrane-bound organelles, and DNA located in a nucleoid region rather than a true nucleus.

Eukaryote

An organism composed of cells that possess a true nucleus bounded by a nuclear envelope, as well as membrane-bound organelles.

Virus

A small non-living obligatory intracellular parasite consisting of DNA or RNA surrounded by a protein shell (capsid), which requires host cells to replicate.

Cellular Metabolism

The sum of all biochemical reactions carried out by a cell or an organism.

Anabolism

Metabolic pathway involving the synthesis of complex molecules from simpler ones, requiring an input of energy ('assembling').

Catabolism

Metabolic pathway involving the breakdown of complex molecules into simpler ones, releasing energy ('breaking down').

Amino Acid

The monomer of proteins, consisting of an $\alpha$-carbon bonded to an amino group ($\text{NH}_2$), a carboxyl group ($\text{COOH}$), a hydrogen atom, and a variable side chain ($R\text{-group}$).

Polypeptide

A linear polymer of amino acids linked by peptide bonds, representing the primary structure of a protein.

Denaturation

The loss of a protein's three-dimensional conformation (3D shape) resulting in a loss of function, caused by alterations in pH, salt concentration, or temperature.

Enzyme

A biological catalyst (usually a protein) that speeds up specific biochemical reactions without being consumed in the process.

Active Site

The specific region on an enzyme that binds the substrate and catalyzes the chemical reaction.

Substrate

The specific reactant molecule upon which an enzyme acts.

Induced Fit

The slight change in shape of an enzyme's active site upon binding to a substrate, enabling it to fit tightly around the substrate to catalyze the reaction.

Activation Energy ($E_a$)

The initial energy required to break bonds and initiate a chemical reaction, which is lowered by the presence of an enzyme.

Adenosine Triphosphate (ATP)

The primary cellular energy molecule composed of adenine, ribose, and three phosphate groups, which releases energy for cellular work when phosphate bonds are hydrolyzed.

Cellular Work

Any cellular activity requiring energy input, categorized into three types: chemical work, transport work, and mechanical work.

Fluid Mosaic Model

The structural model of the plasma membrane describing it as a fluid bilayer of phospholipids embedded with various functional proteins.

Phospholipid

An amphipathic molecule with a hydrophilic head (glycerol, phosphate group, polar group) and two hydrophobic fatty acid tails, forming the structural basis of cell membranes.

Simple Diffusion

Passive transport in which hydrophobic molecules (such as $\text{O}_2$, $\text{CO}_2$, or testosterone) pass directly through the phospholipid bilayer down their concentration gradient.

Facilitated Diffusion

Passive transport of hydrophilic or polar molecules across a membrane down their concentration gradient via specific channel or carrier proteins.

Osmosis

The diffusion of water molecules across a selectively permeable membrane from a solution with a lower solute concentration to one with a higher solute concentration.

Aquaporin

A specialized channel protein that facilitates the rapid passage of water ($\text{H}_2\text{O}$) molecules across the plasma membrane.

Active Transport with Pump

Membrane transport that moves ions or molecules against their concentration gradient across a membrane, requiring energy (such as $\text{ATP}$) and transport proteins (e.g., $\text{Na}^+/\text{K}^+$ pump).

Exocytosis

Active vesicular transport process in which intracellular vesicles fuse with the plasma membrane to export substances out of the cell.

Endocytosis

Active vesicular transport process in which the cell engulfs external material by invaginating its plasma membrane to form intracellular vesicles.

Cytoskeleton

A network of protein fibers in the cytoplasm that provides structural support, anchors organelles, and facilitates intracellular transport and movement.

DNA Nucleotide

The monomer of DNA, composed of a nitrogenous base (adenine, thymine, cytosine, or guanine), a deoxyribose sugar, and a phosphate group.

DNA Replication

The semi-conservative process occurring during interphase (S phase) in which parent DNA strands separate to serve as templates for synthesizing two identical double-stranded DNA molecules.

DNA Polymerase

The enzyme that catalyzes the synthesis of new DNA strands by joining complementary nucleotides to the template strand during replication.

Polymerase Chain Reaction (PCR)

An in vitro molecular biology technique using a heat-stable DNA polymerase (Taq polymerase) to rapidly produce over a billion copies of a targeted DNA segment in less than an hour.

Interphase

The non-dividing phase of the cell cycle (comprising $\text{G}_1$, S, and $\text{G}_2$ phases) during which the cell grows, synthesizes organelles and proteins, and replicates its DNA.

Sister Chromatids

Two identical copies of a replicated chromosome joined together at the centromere.

Centromere

The specialized region of a replicated chromosome where two sister chromatids are held together and attached to spindle fibers.

Mitosis

The division of the mother cell's nucleus into two genetically identical daughter nuclei, consisting of prophase, metaphase, anaphase, and telophase.

Cytokinesis

The division of the cytoplasm following mitosis, accomplished in animal cells by a cleavage furrow and in plant cells by a cell plate.

Apoptosis

A process of programmed cell death used to destroy damaged, unneeded, or dangerous cells (such as cancerous cells).

HeLa Cells

An immortal line of human cervical cancer cells isolated in $1951$ from Henrietta Lacks, widely used in biomedical research.

Aerobic Cellular Respiration

A catabolic pathway that uses oxygen ($\text{O}_2$) to break down organic molecules (such as glucose), yielding $\text{CO}_2$, $\text{H}_2\text{O}$, and up to $30$ to $32\,\text{ATP}$.

Glycolysis

The initial stage of cellular respiration occurring in the cytosol that splits one glucose molecule into two pyruvate molecules, generating a net yield of $2\,\text{ATP}$ and $2\,\text{NADH}$.

Pyruvate Oxidation

The mitochondrial matrix step that converts pyruvate into acetyl-CoA, releasing $\text{CO}_2$ and producing $\text{NADH}$.

Citric Acid Cycle

A cyclic metabolic pathway in the mitochondrial matrix that fully breaks down acetyl-CoA into $\text{CO}_2$, generating $\text{ATP}$, $\text{NADH}$, and $\text{FADH}_2$.

Chemiosmosis

The process in which the movement of protons ($\text{H}^+$) down their electrochemical gradient across the inner mitochondrial membrane drives ATP synthesis via ATP synthase.

ATP Synthase

A membrane enzyme complex that uses the kinetic energy of protons ($\text{H}^+$) flowing down their concentration gradient to catalyze the phosphorylation of ADP into ATP.

Fermentation

An anaerobic catabolic pathway in the cytosol that regenerates $\text{NAD}^+$ from pyruvate, allowing glycolysis to continue yielding $2\,\text{ATP}$ per glucose in the absence of $\text{O}_2$.

Transcription

The synthesis of a pre-messenger RNA ($\text{pre-mRNA}$) molecule from a DNA template strand catalyzed by RNA polymerase inside the nucleus.

RNA Polymerase

The enzyme that separates DNA strands and links RNA nucleotides complementary to the DNA template strand during transcription.

Pre-mRNA Processing (Maturation)

The modification of nuclear pre-mRNA involving the addition of a $5'$ GTP cap, a $3'$ poly-A tail, intron splicing, and exon joining to produce functional mRNA.

Intron

A non-coding segment of DNA/pre-mRNA that is excised during RNA processing before translation.

Exon

A coding segment of DNA/mRNA that remains after splicing and is translated into an amino acid sequence.

Codon

A three-nucleotide sequence in mRNA that specifies a particular amino acid or a start/stop signal during translation.

Translation

The synthesis of a polypeptide chain by a ribosome in the cytoplasm or on the rough endoplasmic reticulum using the codon sequence of an mRNA molecule.

Ribosomal Sites (E, P, A)

Functional sites on the large ribosomal subunit: the A site binds incoming aminoacyl-tRNA, the P site holds the peptidyl-tRNA attached to the growing polypeptide, and the E site releases discharged tRNAs.

Transfer RNA (tRNA)

An RNA molecule featuring a specific anticodon at one end and an amino acid attachment site at the other, delivering amino acids to the ribosome during translation.

Operon

A cluster of genes under the control of a single promoter in prokaryotes (e.g., E. coli), allowing coordinated gene regulation.

Point Mutation

A genetic mutation involving a change in a single nucleotide pair in DNA.

Silent Mutation

A point mutation that alters a codon but results in the same amino acid due to the redundancy of the genetic code, causing no functional change.

Missense Mutation

A point mutation that alters a codon so that it codes for a different amino acid in the resulting protein.

Nonsense Mutation

A point mutation that changes an amino acid codon into a premature stop codon, terminating translation early.

Frameshift Mutation

A mutation caused by the insertion or deletion of nucleotides (not divisible by three), altering the reading frame for all subsequent codons.

Meiosis

A two-stage nuclear division process in diploid ($2n$) germ cells that produces four genetically unique haploid ($n$) gametes.

Somatic Cell

Any biological cell forming the body of a multicellular organism that is not a reproductive cell (diploid, $2n = 46$ in humans).

Gamete

A haploid ($n = 23$ in humans) reproductive cell, such as a sperm or egg cell, formed through meiosis.

Homologous Chromosomes

A pair of chromosomes of equal length and gene loci—one inherited from the mother and one from the father.

Crossing Over (Enjambement)

The reciprocal exchange of genetic material between non-sister chromatids of homologous chromosomes during prophase I of meiosis, creating recombinant chromosomes.

Independent Assortment

The random orientation and segregation of homologous chromosome pairs at metaphase I (and sister chromatids at metaphase II) during meiosis, generating genetic diversity in gametes.

Nondisjunction

An error during meiosis I or II in which homologous chromosomes or sister chromatids fail to separate properly, resulting in gametes with an abnormal chromosome number (e.g., trisomy 21).

Allele

An alternative version of a gene located at a specific locus on a chromosome.

Locus

The specific physical location of a gene on a chromosome.

Genotype

The genetic makeup or combination of alleles present in an organism for a specific gene.

Phenotype

The observable physical, physiological, or biochemical traits of an organism determined by its genotype and environment.

Homozygous

Having two identical alleles for a given gene (e.g., $VV$ or $vv$).

Heterozygous

Having two different alleles for a given gene (e.g., $Vv$).

Complete Dominance

An allelic interaction where the phenotype of the heterozygote is identical to the dominant homozygote, completely masking the recessive allele.

Incomplete Dominance

An allelic interaction where the phenotype of a heterozygote is an intermediate blend between the phenotypes of the two homozygotes (e.g., red and white flowers yielding pink flowers).

Codominance

An allelic interaction in which both alleles in a heterozygote are fully and simultaneously expressed in the phenotype (e.g., AB blood type).

Epistasis

A gene interaction where a gene at one locus alters or masks the phenotypic expression of a gene at a second locus (e.g., coat color in Labrador retrievers).

Polygenic Inheritance

An additive effect of two or more genes on a single phenotypic character, producing continuous variation in a population (e.g., human skin color or height).

Sex-Linked Inheritance

The inheritance of a gene located on a sex chromosome (heterosome), usually the X chromosome (e.g., red-green colorblindness, hemophilia).

Pedigree (Lignage)

A family tree diagram showing the occurrence and inheritance of phenotypic traits across multiple generations.

Recessive Epistasis

A form of gene interaction in which homozygous recessive alleles at one gene locus ($ee$) suppress the expression of alleles at another gene locus ($N$/$n$), resulting in a $9:3:4$ phenotypic ratio in a dihybrid cross.