Comprehensive MCAT Biology: Cell Structure, Genetics, and Reproduction

Cell Theory

4 Tenets: 1. All living things are made of cells 2. Cells come from preexisting cells through division 3. Cells carry genetic information in the form of DNA that is passed from parent to daughter cells 4. The cell is the fundamental unit of life

Cell Theory Tenet 1

All living things are made of cells.

Cell Theory Tenet 2

Cells come from preexisting cells through division.

Cell Theory Tenet 3

Cells carry genetic information in the form of DNA that is passed from parent to daughter cells.

Cell Theory Tenet 4

The cell is the fundamental unit of life.

Eukaryotes

Organisms with membrane-bound organelles, nuclei, and can be single celled or multicellular.

Cytoplasm

The area that fills the cells, the area in between the organelles and the cell membrane.

Cytosol

The fluid that is within the cytoplasm.

Nucleus

A double membraned organelle that contains DNA and has pores for material exchange.

Nuclear envelope

The entire structure that separates the inside of the nucleus from the cytoplasm.

Histones

Proteins around which DNA is wrapped to organize it in the nucleus.

Nucleolus

Small part of the nucleus specific for the synthesis of ribosomal RNA (rRNA).

Ribosomes (nucleolus)

Formed in the nucleolus but are immature/inactive until leaving the nucleus and making it to their destination.

Mitochondria

Double membraned organelle that is the powerhouse of the cell, doing many metabolic energy producing processes.

Cristae

Foldings of the inner mitochondrial membrane that increase its surface area for chemical reactions.

Matrix

The area within the inner mitochondrial membrane, similar to cytosol.

Apoptosis

Programmed cell death that is initiated by the mitochondria.

Lysosomes

Cell cleaners that have hydrolytic enzymes to break down ingested materials or waste products.

Autolysis

Release of lytic enzymes within the lysosomes, leading to the lysis of cells.

Endoplasmic Reticulum

Connected membranes that synthesize important cellular components like proteins and lipids.

Rough ER

Has membrane-bound ribosomes which translate proteins that will be secreted out of cells.

Smooth ER

Contains no ribosomes, used for the synthesis of lipids and detoxification.

Golgi apparatus

Membrane bound sacs that can modify, package, and direct cellular products.

Cisternae

Layers of the Golgi apparatus, ordered as cis, medial, trans.

Peroxisomes

Contain hydrogen peroxide for oxidative purposes in metabolism.

Prokaryotes

Organisms without membrane bound organelles that replicate via binary fission.

Binary fission

Division of a prokaryotic/bacterial cell into two identical daughter cells.

Nucleoid region

A region within the cell of prokaryotes where genetic material is condensed.

Ribosomes in prokaryotes

Smaller than eukaryotes, made up of 30S and 50S subunits forming a 70S ribosome.

Svedberg unit

Unit for sedimentation, describing the behavior of ribosomal subunits in sedimentation.

Plasmids

Small, extrachromosomal circular DNA segments that can contain antibiotic resistance or virulence factors.

Virulence factor

Some sort of molecule that allows bacteria to become more pathogenic.

Episome

A specific type of plasmid that can integrate itself into the genome.

Lateral (horizontal) gene transfer

Ways for bacteria/prokaryotes to increase genetic diversity.

Transformation

Uptake of DNA from the surroundings of the bacteria.

Conjugation

Transfer of a DNA plasmid through a conjugation bridge.

F+ cell

A cell containing the plasmid that can transfer it to an F- cell.

Hfr cells

High frequency recombinant cells that transfer a portion of the genome.

Transduction

Transfer of DNA from one bacterium to another due to infection by a virus.

Transposons

Stretches of genes that can insert or remove themselves from one chromosome to another.

Bacterial Resistance

When bacteria become resistant to medications, allowing them to survive.

Recombinant Proteins

Artificially produced proteins made by giving viruses or bacteria the gene for the protein.

Obligate aerobes

Bacteria that require oxygen for growth.

Obligate anaerobes

Bacteria that cannot exist in the presence of oxygen.

Aerotolerant anaerobes

Bacteria that can live in oxygen's presence but do not use it.

Facultative anaerobes

Bacteria that can sometimes use oxygen in metabolism.

Growth Cycle (4)

lag phase, log phase, stationary phase, death phase

Lag phase

The phase where bacterial colony adapts to conditions without significant growth.

Log (exponential) phase

The phase where bacterial growth increases exponentially.

Stationary phase

The phase where the bacterial colony reaches the carrying capacity of its environment.

Death phase

The phase where the bacterial colony begins dying due to lack of resources.

Archaea

A type of prokaryote that lives in harsh environments.

Bacteria

The other division of prokaryotes that can be mutualistic symbiotes to humans.

Shapes of bacteria

Cocci (spherical), bacilli (rod-shaped), and spirilla (spiral).

Flagella

Structure made of a protein called flagellin that allows bacterial movement.

Cell wall

A thick layer that provides additional structure and function to bacterial cells.

Peptidoglycan

A polymer unique to prokaryotes that makes up the cell wall of bacteria.

Gram-staining

A lab technique to determine the type of bacteria based on stain retention.

Gram positive (+)

Bacteria with a thick cell wall that retains the purple stain.

Exotoxins

Toxic substances secreted by bacteria into the surrounding medium.

Gram negative (-)

Bacteria with a thin cell wall and two separate cell membranes.

Lipopolysaccharides (LPS)

Components of the cell wall of gram-negative bacteria, also known as endotoxins.

Endotoxins

Molecules like lipopolysaccharides that cause toxic reactions such as inflammation and fever when bacteria are ingested.

Gram Stains

A lab technique where Gram positive bacteria appear purple due to a thick wall, while Gram negative bacteria appear pink due to a thin wall.

Bacteria vs Archaebacteria

Both are prokaryotes, but Archaea lack peptidoglycan in their cell walls, live in extreme environments, and have diverse metabolic pathways resembling eukaryotic cells.

Cytoskeleton

A structure that provides stability and rigidity for all types of cells, important in cellular transport.

Microfilaments

Polymers of actin important for cell structure and protection, aiding in the formation of the cleavage furrow in cytokinesis.

Microtubules

Polymers of tubulin that serve as paths for cellular transport proteins and are part of the structure of cilia and flagella.

Kinesin

A protein that carries cellular components anterograde (away from the nucleus).

Dynein

A protein that carries cellular components retrograde (towards the nucleus).

Cilia

Hair-like structures that cause cellular movements and sweeping motions of the surroundings.

Centrioles

Complexes involved in the microtubule organization of the mitotic spindle during mitosis.

Intermediate Filaments

Molecules important for cell-to-cell adhesion and anchoring of organelles, such as keratin and desmin.

Keratin

An intermediate filament protein important in waterproofing cells, especially in the epidermis.

Epithelia

Tissue that covers the body and lines its cavities, providing protection against physical stress and pathogens.

Simple Epithelia

Epithelial tissue consisting of a single layer of cells.

Stratified Epithelia

Epithelial tissue consisting of multiple layers of cells.

Pseudostratified Epithelia

Epithelial tissue that appears to have multiple layers due to varying cell heights but actually consists of one layer.

Cuboidal Epithelia

Epithelial cells shaped like a cube.

Columnar Epithelia

Epithelial cells that are more rectangular in shape.

Squamous Epithelia

Epithelial cells that are flat and do not have a square or rectangular shape.

Parenchyma

The epithelial tissue that lines the organs or secretory parts of the organs.

Cell Membrane

A phospholipid bilayer that forms a sphere with hydrophilic heads facing outward and hydrophobic tails inward.

Phospholipids

Molecules with a polar/hydrophilic phosphate head and two nonpolar/hydrophobic fatty acid tails.

Cholesterol

A molecule that can increase or decrease membrane fluidity, acting as a temperature buffer for the phospholipid membrane.

Membrane Permeability

The property of the membrane being semi-permeable, allowing certain molecules to pass while restricting others.

Peripheral Proteins

Proteins that are noncovalently bonded to the outside of the membrane with transient interactions.

Integral/Transmembrane Proteins

Proteins that cross the whole membrane and are bonded in strong hydrophobic interactions with the fatty acid tails.

Nonpolar amino acids

Amino acids that face outwards in nonpolar environments like the bilayer.

Polar and charged amino acids

Amino acids that face outwards in polar environments like water or cytosol.

Lipid-anchored proteins

Proteins on the surface of the membrane covalently attached to lipids within the membrane.

Channel Proteins

Transmembrane proteins that allow the passing of specific types of molecules upon conformational change.

Voltage Gated

Channels regulated by a voltage threshold.

Ligand Gated

Channels regulated by a specific type of molecule binding to the channel protein.

Na/K ATPase

Ion transporter that pumps 3 Na out of the cell and 2 K in, at the cost of 1 ATP.

Aquaporin

Transmembrane proteins that increase the flow rate of water down its gradient.

Porin

Broad type of protein that forms channels.

Leak Channel

Passive channels that are always open.

Carrier Protein

Proteins that transport molecules needing protection from the environment.

Ion Pump/Transporter

Capable of moving ions and other small molecules across membranes.