MCAT Prep Biology Review

What are the four tenets of cell theory?

1) All living things are composed of cells.

2) The cell is the basic functional unit of life.

3) Cells arise only from preexisting cells.

4) Cells carry genetic information in the form of DNA.

What distinguishes eukaryotic cells from prokaryotic cells?

Eukaryotic cells have membrane-bound organelles, including a nucleus, while prokaryotic cells do not.

What is the function of the nucleus in a eukaryotic cell?

The nucleus stores DNA, which is organized into chromosomes, and serves as the site of transcription.

What is the nucleolus and its function?

The nucleolus is a dense region within the nucleus where ribosomal RNA (rRNA) is synthesized.

What is the role of mitochondria?

Mitochondria are the site of aerobic respiration and produce ATP; they can also initiate apoptosis.

What are lysosomes?

Lysosomes are membrane-bound organelles containing hydrolytic enzymes for digestion of cellular waste and apoptosis.

What is the function of the endoplasmic reticulum (ER)?

Rough ER synthesizes proteins; smooth ER synthesizes lipids and detoxifies drugs/poisons.

What is the Golgi apparatus?

A system of membranes that modifies, packages, and ships proteins and lipids from the ER.

What is the function of peroxisomes?

Peroxisomes contain hydrogen peroxide and are involved in fatty acid β-oxidation.

What three components make up the cytoskeleton?

Microfilaments (actin), microtubules (tubulin), and intermediate filaments.

What are epithelial tissues?

Tissues that cover the body and line cavities; involved in absorption, secretion, and sensation.

What are connective tissues?

Tissues that support the body and provide a framework for epithelial cells (e.g., bone, cartilage, tendons).

What is the difference between archaea and bacteria?

Archaea are extremophiles and use alternative energy sources; bacteria are prokaryotic, with a variety of shapes and metabolic strategies.

What are the three shapes of bacteria?

Cocci (spherical), bacilli (rod-shaped), spirilli (spiral-shaped)

Define

obligate aerobe,

obligate anaerobe

facultative anaerobe

aerotolerant anaerobe.

Obligate aerobe requires oxygen.

Obligate anaerobe cannot survive in oxygen.

Facultative anaerobe toggles between.

Aerotolerant anaerobe ignores O₂.

What is binary fission?

Asexual reproduction method used by prokaryotes involving replication and division into two identical daughter cells.

What are the methods of genetic recombination in bacteria?

Transformation (uptake from environment),

conjugation (via sex pilus)

transduction (via bacteriophages).

What is a plasmid?

An extrachromosomal DNA molecule in bacteria that may contain antibiotic resistance or virulence factors.

What is the structure of a virus?

A virus consists of genetic material (DNA or RNA), a protein coat (capsid), and sometimes a lipid envelope.

What are retroviruses?

Viruses that use reverse transcriptase to integrate into the host genome (e.g., HIV)

What are prions and viroids?

Prions are misfolded proteins that cause disease.

Viroids are small, circular RNA molecules that infect plants.

What is the cell cycle?

The series of phases (G₁, S, G₂, M) through which a cell grows, duplicates its DNA, and divides.

What happens during the G₁ stage?

The cell grows, carries out normal functions, and prepares for DNA synthesis; a restriction point checks for DNA damage.

What occurs in the S stage of the cell cycle?

DNA is replicated; each chromosome becomes two sister chromatids bound at a centromere.

What is the function of the G₂ stage?

Final cell growth and another quality checkpoint before mitosis

What are the phases of mitosis?

• Prophase: Chromosomes condense, spindle forms, nuclear membrane dissolves

• Metaphase: Chromosomes align at the metaphase plate

• Anaphase: Sister chromatids separate

• Telophase: Nuclear membrane reforms, chromosomes decondense

What is cytokinesis?

Division of the cytoplasm and organelles, completing cell division.

What is the main difference between mitosis and meiosis?

Mitosis results in two genetically identical diploid cells; meiosis yields four non-identical haploid gametes.

What is meiosis I?

Reductional division: homologous chromosomes are separated, reducing ploidy.

What is meiosis II?

Equational division: sister chromatids are separated, like mitosis.

What is synapsis?

Pairing of homologous chromosomes to form a tetrad in prophase I.

What is crossing over?

Exchange of genetic material between homologous chromatids during prophase I, increasing genetic diversity.

What is disjunction and when does it occur?

Separation of homologous chromosomes in anaphase I of meiosis; responsible for Mendel’s Law of Segregation.

What is Mendel’s Second Law (of Independent Assortment)?

Alleles for separate traits assort independently; explained by crossing over.

What are the phases of the menstrual cycle?

• Follicular phase: FSH stimulates follicle growth

• Ovulation: LH surge triggers release of ovum

• Luteal phase: Corpus luteum secretes progesterone

• Menses: If no fertilization, shedding occurs

What is the function of follicle-stimulating hormone (FSH)?

Stimulates follicle maturation (females) and spermatogenesis (males).

What is the function of luteinizing hormone (LH)?

Triggers ovulation (females) and testosterone production (males).

What are primary sex characteristics?

Reproductive organs and structures (testes, ovaries, penis, uterus).

What are secondary sex characteristics?

Traits that emerge during puberty (e.g., breasts, voice changes, body hair).

What is the function of testosterone?

Stimulates sperm production and development of male secondary sex characteristics.What is estrogen responsible for?

What is estrogen responsible for?

Development of female reproductive tract and secondary sex characteristics; also thickens the endometrium.

What is the function of progesterone?

Maintains the endometrial lining for possible implantation.

What is menopause?

Cessation of menstruation due to decreased estrogen and progesterone, typically occurring around age 45–55.

What is spermatogenesis and where does it occur?

The production of sperm in the seminiferous tubules of the testes.

What is oogenesis?

The production of female gametes (ova) that begins prenatally and completes after fertilization.

What is the acrosome?

A cap on the sperm head derived from the Golgi apparatus, containing enzymes to penetrate the ovum.

What is fertilization?

The fusion of a sperm and secondary oocyte (in metaphase II) to form a zygote, typically in the ampulla of the fallopian tube.

What is the acrosomal apparatus?

A tubelike structure formed by sperm after it makes contact with the ovum; penetrates the oocyte’s membrane.

What is the cortical reaction?

Release of calcium ions after fertilization to depolarize the ovum membrane, preventing polyspermy and increasing metabolic rate of the zygote.

What are dizygotic (fraternal) twins?

Twins from two separate eggs and two separate sperm; genetically distinct.

What are monozygotic (identical) twins?

Twins that originate from one zygote splitting into two embryos; genetically identical.

What is cleavage in embryogenesis?

Rapid mitotic cell divisions of the zygote after fertilization, increasing the nuclear-to-cytoplasmic (N:C) and surface area-to-volume ratios.

What is the difference between determinate and indeterminate cleavage?

• Indeterminate cleavage: Cells can become any cell type (totipotent).

• Determinate cleavage: Cell fates are already committed.

What is a morula?

A solid ball of cells resulting from cleavage.

What is a blastula (blastocyst)?

A hollow ball of cells with a fluid-filled inner cavity (blastocoel); implants in the endometrium.

What are the two cell groups in a blastocyst?

• Trophoblast: Becomes the placenta

• Inner cell mass: Becomes the embryo

What are chorionic villi?

Projections from the trophoblast that penetrate the endometrium and form the fetal portion of the placenta.

What is the umbilical cord?

A cord with two arteries and one vein that connects embryo to placenta; vein carries oxygenated blood.

What is the amnion?

A thin, tough membrane filled with amniotic fluid that cushions the embryo.

What is gastrulation?

The process by which a blastula develops into a gastrula with three germ layers.

What is the archenteron?

The primitive gut formed during gastrulation.

What is the blastopore?

The opening of the archenteron; becomes the anus in deuterostomes and the mouth in protostomes.

What are the three primary germ layers and what do they form?

• Ectoderm: Skin, nervous system, eyes

• Mesoderm: Muscles, bones, circulatory system

• Endoderm: Digestive and respiratory epithelium, liver, pancreas

What is neurulation?

The development of the nervous system from the ectoderm.

What is the notochord?

A rod of mesodermal cells that induces formation of the neural tube from ectoderm.

What are neural crest cells?

Cells at the tip of the neural fold that migrate to form the peripheral nervous system, melanocytes, and facial cartilage.

What are teratogens?

Substances that interfere with normal development and cause birth defects (e.g., alcohol, viruses, drugs).

What is differentiation?

The process by which cells become specialized in structure and function.

What is potency?

A cell’s ability to differentiate into other cell types:

• Totipotent → any cell (zygote)

• Pluripotent → any germ layer cell

• Multipotent → only specific lineages

What are stem cells?

Undifferentiated cells with the potential to become different cell types depending on potency.

What is cell induction?

The influence of one group of cells on the differentiation of another through inducers.

What are morphogens?

Molecules that diffuse through tissues and influence cell fate by creating gradients.

What are apoptotic blebs and bodies?

Membrane-bound fragments formed during apoptosis; digested by phagocytes to prevent inflammation.

What is necrosis?

Uncontrolled cell death due to injury, causing cell contents to leak and potentially triggering inflammation.

What is regenerative capacity?

The ability of an organism to regrow certain parts:

• Complete regeneration: Identical replacement (e.g., salamanders)

• Incomplete regeneration: Tissue is not identical (e.g., humans)

What is senescence?

Biological aging due to shortened telomeres, oxidative stress, and loss of cell division capacity.

What are the two fetal circulatory structures that bypass the lungs?

• Foramen ovale: Right atrium → left atrium

• Ductus arteriosus: Pulmonary artery → aorta

What is the ductus venosus?

A shunt that bypasses the fetal liver; directs blood from the umbilical vein directly to the inferior vena cava.

What is a neuron?

A specialized cell that transmits electrical impulses and translates them into chemical signals.

What is the soma of a neuron?

The cell body that contains the nucleus and organelles (e.g., ER, ribosomes).

What are dendrites?

Branchlike structures that receive incoming signals from other neurons.

What is the axon hillock?

The region of the neuron where the cell body transitions to the axon and where action potentials are initiated.

What is an axon?

A long projection from the soma that carries electrical signals toward the synaptic terminal

What is myelin and its function?

A fatty membrane that insulates axons and speeds up signal conduction.

What are oligodendrocytes and Schwann cells?

• Oligodendrocytes: Form myelin in the CNS

• Schwann cells: Form myelin in the PNS

What are nodes of Ranvier?

Gaps between segments of myelin sheath where ion channels are concentrated; allow saltatory conduction.

What is the synaptic bouton (nerve terminal)?

The end of the axon that releases neurotransmitters into the synaptic cleft.

What is the synapse?

The junction between two neurons consisting of the presynaptic membrane, synaptic cleft, and postsynaptic membrane.

What are glial cells (neuroglia)?

Supportive cells in the nervous system that perform various functions.

What are astrocytes?

Glial cells that nourish neurons and maintain the blood–brain barrier.

What are ependymal cells?

Line the ventricles of the brain and produce cerebrospinal fluid (CSF).

What are microglia?

Phagocytic immune cells in the CNS.

What is the resting membrane potential?

The electrical potential difference across the membrane at rest, usually around –70 mV.

What ions maintain resting potential?

High K⁺ inside and high Na⁺ outside; maintained by the Na⁺/K⁺ ATPase.

What is depolarization?

A rise in membrane potential due to influx of Na⁺ ions.

What is threshold potential?

The membrane potential (~–55 mV) that must be reached to initiate an action potential.

What is an action potential?

A rapid, all-or-none depolarization and repolarization of the membrane that propagates along the axon.

What happens during repolarization?

K⁺ exits the cell to restore negative membrane potential.

What is hyperpolarization?

Overshoot of membrane potential below resting value due to prolonged K⁺ efflux.

What is the refractory period?

• Absolute: No stimulus can cause another AP

• Relative: A stronger stimulus can trigger an AP