PCAT

This section reviews the general and advanced biology concepts that pharmaceutical sciences build on: cellular and molecular biology, genetics, the diversity of life, microbiology, the structure and function of body systems, developmental biology, evolution, ecology, behavior, and health. A strong college-level understanding of these principles prepares you for physiology, pharmacology, and therapeutics courses.

Cell Theory and Cell Types

Cell theory states that all living organisms are composed of cells, the cell is the basic unit of life, and all cells arise from pre-existing cells. Two primary cell types exist.

Prokaryoticvs.Eukaryoticcells

Feature	ProkaryoticCells	EukaryoticCells
Nucleus	None;DNAliesinthenucleoidregion	Membrane-bound nucleus
Organelles	No membrane-bound organelles	Many membrane-bound
		organelles
Geneticmaterial	Singlecircularchromosome;maycarryplasmids(smallcircular	Multiplelinearchromosomes
	DNA)
Ribosomes	70S(30S+50Ssubunits)	80S(40S+60Ssubunits)
Size	Generallysmaller	Largerandmorecomplex
Examples	Bacteriaandarchaea	Animals plants fungi andprotists , , ,

The difference between 70S and 80S ribosomes is exploited by antibiotics: several drug classes bind bacterial ribosomal subunits and block protein synthesis in bacteria while leaving human ribosomes largely unaffected.

Cell Organelles and Functions

Organelle	Function
Nucleus	Containsthecell'sDNAandisthesiteoftranscription Thenuclearenvelopehasporesfortransport; .
	thenucleolussynthesizesribosomalRNA .
Mitochondria	Sitesofaerobiccellularrespiration;produceATPbyoxidativephosphorylation Havetheirown .
	circularDNAandadoublemembrane;theinnermembranefoldsintocristaethatincreasesurface
	areaforATPsynthesis .
Ribosomes	Sitesofproteinsynthesis;freeinthecytoplasmorattachedtotheroughER .
RoughER	Studdedwithribosomes;synthesizesandmodifiesproteins .
SmoothER	Lacksribosomes;synthesizeslipidsanddetoxifiesdrugsandpoisons .
Golgiapparatus	Modifies sorts packages andshipsproteinsandlipidstotheirdestinations:thecell'spostalsystem , , , .
Lysosomes	Containdigestiveenzymesinanacidicinterior;breakdownwaste foreignmaterial andold , ,
	organelles(autophagy) .
Peroxisomes	Breakdownfattyacidsandaminoacidsandneutralizetoxicsubstancessuchashydrogenperoxide .
Cellmembrane	Phospholipidbilayerwithembeddedproteins;controlsselectivepermeability cellsignaling and , ,
	transport Thefluidmosaicmodeldescribesitsdynamicstructure . .

Membrane Transport

Requires no energy; moves substances down their

Requires energy (ATP) and moves substances against their

concentration gradient. Simple diffusion moves small,

gradient; the sodium-potassium pump is the classic example.

nonpolar molecules through the bilayer; facilitated diffusion Endocytosis and exocytosis move large molecules or particles

uses channel or carrier proteins; osmosis is the diffusion of

in and out of the cell in vesicles.

water across a semipermeable membrane.

Cell Cycle and Mitosis

The cell cycle consists of interphase and the mitotic phase. Interphase includes G1 (cell growth), S (DNA replication), and G2 (preparation for division). The mitotic phase includes mitosis and cytokinesis.

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Chromatin condenses;

Chromosomes align at

Sister chromatids

Nuclear envelopes

The cytoplasm divides

the spindle forms

the metaphase plate

separate to the poles

reform; chromosomes

decondense

Checkpoints regulate progression through the cycle. The G1 checkpoint ensures the cell is large enough and its DNA is undamaged, the G2 checkpoint ensures DNA replication is complete, and the spindle assembly checkpoint ensures every chromosome is attached to the spindle.

DNA Structure and Replication

DNA is a double helix of nucleotides, each containing a deoxyribose sugar, a phosphate group, and a nitrogenous base. Adenine pairs with thymine (two hydrogen bonds) and guanine pairs with cytosine (three hydrogen bonds). Replication is semiconservative: each new double helix has one original strand and one new strand.

Enzyme	Role
Helicase	Unwindsthedoublehelix
Primase	SynthesizesRNAprimers
DNApolymerase	SynthesizesnewDNAstrandsinthe5′to3′direction
Ligase	JoinsOkazakifragmentsonthelaggingstrand

Transcription and Translation

RNA polymerase synthesizes mRNA from the DNA template

mRNA codons are read 5′ to 3′. Each tRNA carries an amino

strand, starting at the promoter. The mRNA is processed: a 5′

acid and has an anticodon complementary to the codon.

cap and poly-A tail are added, introns are removed, and exons

Translation begins at the start codon AUG (methionine) and

are spliced together.

ends at a stop codon: UAA, UAG, or UGA.

Enzymes

Enzymes are biological catalysts that lower the activation energy of reactions. They are specific to their substrates, which bind at the active site to form an enzyme-substrate complex. Activity depends on temperature, pH, substrate concentration, and the presence of inhibitors.

Cellular Respiration

Aerobic respiration converts glucose and oxygen into ATP, carbon dioxide, and water in three main stages.

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Cytoplasm · glucose → 2 pyruvate · net 2 ATP,

Mitochondrial matrix · per glucose: 6 CO2, 2

Inner membrane · ETC + ATP synthase · O2 is

2 NADH

ATP, 8 NADH, 2 FADH2 (including pyruvate

the final electron acceptor

oxidation)

In oxidative phosphorylation, NADH and FADH2 donate electrons to the electron transport chain, which pumps protons to build a gradient. ATP synthase uses this gradient (chemiosmosis) to make ATP, and oxygen accepts the electrons to form water. The total yield is approximately 30–32 ATP per glucose.

Photosynthesis

Genetics