MCAT Biology Review 2025-26

1665 Robert Hooke

assembled microscope and found cells

1674 Leewenhock

1st man to view living cells

Tenets of Cell Theory

1. All living things are composed of ccells

2. cell is the most basic unit of life

3. cells arise only from pre-exisiting cells

4. cells carry genetic information in DNA form to be passed onto daughter cells

What tenets of cell theory do viruses violate that make them non-living?

1. cells arise only from pre-exisiting cells

2. cells carry genetic information in DNA form to be passed onto daughter cells

Eukaryotic Cells

• in multi cell orginisms

• nucleus enclosed in membrane

• membrane bound organelles=> compartmentalization of function

• reproduced by mitosis

cytosol

liquid that allows diffusion of molecules through cell

nucleus

Function: holds the genetic material encoded in DNA which is organized into chromosomes

• surrounded by nucleus membrane

• nuclear pores in membrane allow for selective material to enter and leave

• DNA has coding regions called genes wound against proteins called histomes

nucleolus

Function: Rrna Synthesis

• 25% of the colume of nucleus, the darker spot

mitochondria

Function: provides energy for the cell and performs apoptosis

• orginated in prokoyatic cell

• semi autonomous

  • has its own genes

  • replicates independently

  • cytoplasmic inheritance

• outer-membrane → The Matrix → inner-membrane (contains Electron Transport Chain material)

Lysosomes

Function: causes apoptosis when hydrolytic enzymes are released

• works with endosomes to break down many substrates

Endoplasmic Reticulum (ER)

series of interconnected membranes that are actually contiguous with the nuclear envelope

Rough ER

Function: permits the translation of proteins desired for direct secretion into the lumen

• studded with ribosomes

Smooth ER

Function: lipid synthesis and detox, transports proteins to the golgi

Golgi Apparatus

Function: proteins are modified, repackage products in vesicles, exocytosis

Peroxisomes

Function: contains hydrogen peroxide, breaks down fatty acid chains, sythesis of phosphlipids and enzymes

Cytoskeloton

Function: structure of cell and shape maintenance

Microfilaments

Function: cytokinesis and forms cleavage furrow

• made of actin (resistant to compression and fracture) which provides protection for the cell

• actin filaments can also use ATP

Predominant Protein: actin

Microtubles

Function: provides primary pathways for motor proteins kinesin and dynein to carry vesicles (cilla and flagella)

• hallow polymers of tublin proteins

Predominant Protein: tublin

Flagella

projections from cell involved of the movement of material inside the cell

Cilla

projections from cell involved of the movement of material outside the cell

9 + 2 structure

Flagella and Cilla Both have

• 9 pairs of microtubles in outer ring and two microtubles inside

centrioles

found in centrosome (cell region) and organizing cneters for microtubles and have a hallow center

Intermediate filaments

• cell to cell adhesion or maintenance of the cytoskeleton; anchors organelles

Predominant Protein: keratin and desmin

Epithelial Tissue

Function: provides protection against pathogens & desecration, absorbtion, secretion, and sensation (constitutes the parenchyma or the functional part of the organ)

• polarized (one side facing the lumen or hallow cavity and one side facing outside world)

• different classifications

simple epithelia

one layer of cells

stratified epithelia

multiple layers

psedostratified epithelia

appear to have multiple layers but actually have one

cubidol

cube shaped

columnar

long and thin

squamous

flat and scale like

Basement Membrane

the connective tissue that allows epithelial tissue to be joined together

Connective tissue

suppports the body and provides the framework for the epithelial cells to carry out their functions

• forms the extracelleur matrix

prokaryotes

cells that do not contain membrane bound organelles; they contain their genome in a single circular molecule of DNA located in the nucleoid region

archaea

extremophiles (mostly), often use chemosythesis and similar to both eukaryotes (translation, RNA polymerases, histones) and bacteria (single circular chromosomes, divide by binary fission or budding)

bacteria

similar structures to eukaryotes, complex relationships with humans including mutualistic symbiosis and pathogenesis

Eukarya

is the only non prokaryotic domain

Cocci

spherical bacteria

Bacilli

rod shaped bacteria

Spirilli

spiral shaped bacteria

Obligate aerobes

require oxygen for metabolism

obligate anaerobes

cannot survive in oxygen containing enviroments and can only carry out anaerobic metabolism

facultative anaerobes

can survive in environments with or without oxygen containing environment

aerotolerant anerobes

cannot use oxygen for metabolism, but can survive in oxygen-containing environments

Gram positive bacteria

have a thick cell wall composed of peptidoglycan and lipoteichoic acid

Gram Negative Bacteria

thin cell wall composed of peptidoglycan and an outer membrane containing phospholipids and lipopolysaccharides

Diploid (2n)

cells that have two copies of each chromosomes

Haploid (n)

cells have one copy

interphase

G1, S, G2 phases that is where DNA is uncoiled in the form of chromatin

G_{1 stage}

pre-synthetic gap, cells create organelles for energy and protein production, and increase their size

• Restriction point: during which the DNA is checked for quality, must be passed for the cell to move into the S stage

S (synthesis) stage

further cell growth and replication of organelles in preparation for mitosis, quality checkpoint before mitosis

M stage

mitosis and cytokinesis occurs

G₀ stage

the cell performs its functions without preparing for divsion

p53

plays a role in the two major checkpoints of the cell cycle

Cyclins and Cyclin Dependent Kinases (CDKs)

rise and fall during the cell cycle, cyclins bind to CDKs which activate transcription factors for next stage of cycle

Cancer

when cell cycle control becomes deranged which allows damaged cells to replicate; these type of cells will release factors that allow them to delocalize and invade nearby tissues (metastasize)

Somatic Cell

where mitosis produce two genetic identical diploid daughter cells from a single cell

Prophase

the chromosomes condense, the nuclear membrane dissolves, nucleoli dissapear, centrioles migrate to opposite sides of the cell and the spindle appratus begins to form

— kinetochore of each chromosome is contacted by a spindle fiber