MCAT Biology

Where does fertilization normally occur?

Ampulla of the fallopian tube.

What sperm structure contains enzymes that penetrate the egg?

Acrosome.

Which layers surrounding the egg must sperm penetrate?

Corona radiata and zona pellucida.

What prevents polyspermy after fertilization?

Cortical reaction.

What ion triggers the cortical reaction?

Calcium (Ca²⁺).

What is a pronucleus?

The haploid nucleus contributed by either the sperm or egg before fusion.

What is the morula?

A solid ball of cells produced by cleavage.

What structure develops from the morula?

Blastula (blastocyst in humans).

What is the blastocoel?

Fluid-filled cavity of the blastula.

What part of the blastocyst becomes the embryo?

Inner cell mass.

What part of the blastocyst becomes the placenta?

Trophoblast.

When does implantation occur?

During the blastocyst stage.

What major event occurs during gastrulation?

Formation of the three primary germ layers.

What are the three germ layers?

Ectoderm, mesoderm, and endoderm.

What is the blastopore?

Opening that develops during gastrulation.

What is the archenteron?

Primitive gut cavity formed during gastrulation.

What embryonic structure induces neurulation?

Notochord.

What germ layer gives rise to the nervous system?

Ectoderm.

Neural folds fuse to form what?

Neural tube.

What does the neural tube become?

Central nervous system (brain and spinal cord).

What do neural crest cells become?

Much of the peripheral nervous system.

What major structures arise from ectoderm?

Nervous system, skin, hair, nails, mouth, and anus.

MCAT mnemonic for ectoderm?

Attract-o-derm (skin, hair, nails).

What major structures arise from mesoderm?

Muscle, bone, circulatory system, gonads, adrenal cortex.

MCAT mnemonic for mesoderm?

Move-o-derm.

What major structures arise from endoderm?

GI tract, respiratory tract, bladder, endocrine glands.

MCAT mnemonic for endoderm?

In-do-derm (internal organs).

What is determination?

Commitment of a cell to a developmental fate.

What is differentiation?

Expression of specialized genes after determination.

What is induction?

One group of cells influencing the fate of nearby cells.

What molecules commonly mediate induction?

Growth factors.

Which stem cells can form an entire organism and placenta?

Totipotent stem cells.

Which stem cells can form any body cell but not placental tissue?

Pluripotent stem cells.

Which stem cells can generate several related cell types?

Multipotent stem cells.

Adult stem cells are usually what type?

Multipotent.

Fraternal twins arise from what?

Two separate eggs fertilized by two separate sperm. (Dizygotic)

Identical twins arise from what?

Splitting of a single fertilized egg. (Monozygotic)

Why does fetal hemoglobin (HbF) have a higher oxygen affinity than adult hemoglobin?

To efficiently extract oxygen from maternal blood.

How are oxygen and carbon dioxide exchanged in the placenta?

Diffusion.

Which vessel carries oxygenated blood from the placenta?

Umbilical vein.

Which vessels carry deoxygenated blood to the placenta?

Umbilical arteries.

What fetal shunt allows blood to bypass the lungs between atria?

Foramen ovale.

What fetal shunt connects pulmonary artery to aorta?

Ductus arteriosus.

Which fetal shunt allows blood to bypass the liver?

Umbilical vein directly to the inferior vena cava.

Fertilization occurs in the ______.

Ampulla.

Implantation occurs during the ______ stage.

Blastocyst.

Gastrulation forms the ______.

Three germ layers.

Neurulation forms the ______.

Neural tube.

CNS derives from the ______.

Neural tube.

PNS largely derives from ______.

Neural crest cells.

Muscle and bone derive from ______.

Mesoderm.

GI tract derives from ______.

Endoderm.

Skin and nervous system derive from ______.

Ectoderm.

Foramen ovale bypasses the ______.

Lungs.

Umbilical vein carries ______ blood.

Oxygenated.

Umbilical arteries carry ______ blood.

Deoxygenated.

What protein makes up microfilaments?

Actin.

What protein makes up microtubules?

Tubulin.

What are examples of intermediate filament proteins?

Keratin, vimentin, desmin, lamin.

Where is DNA located in prokaryotes?

The nucleoid region.

What is the function of the nucleolus?

Ribosome production.

Function of rough ER?

Protein synthesis and processing.

Function of smooth ER?

Lipid synthesis and detoxification.

Function of the Golgi apparatus?

Modify, package, and distribute proteins.

Function of lysosomes?

Intracellular digestion and recycling.

Function of peroxisomes?

Breakdown of fatty acids and toxins.

What are centrioles made of?

Nine groups of microtubules.

What are plasmids?

Small circular DNA molecules in prokaryotes not essential for survival.

What is parenchyma?

Functional tissue of an organ.

What is stroma?

Supportive connective tissue.

Difference between simple and stratified epithelium?

Simple = one layer; stratified = multiple layers.

What does pseudostratified mean?

Appears multilayered but is actually one layer.

Obligate aerobe?

Requires oxygen.

Obligate anaerobe?

Dies in oxygen.

Facultative anaerobe?

Can switch between aerobic and anaerobic metabolism.

Aerotolerant anaerobe?

Does not use oxygen but tolerates it.

Gram-positive bacteria stain what color?

Purple.

Gram-positive cell wall characteristic?

Thick peptidoglycan.

Gram-negative bacteria stain what color?

Pink/red.

Gram-negative cell wall characteristic?

Thin peptidoglycan plus outer membrane.

Transformation?

Uptake of genetic material from environment.

Conjugation?

Direct DNA transfer through a conjugation bridge.

Transduction?

DNA transfer via bacteriophage.

What is a transposon?

Mobile genetic element.

What are prions?

Infectious misfolded proteins.

What are viroids?

Plant pathogens made of RNA.

What is a capsid?

Protein coat of a virus.

Positive-sense RNA virus?

RNA can be translated directly.

Negative-sense RNA virus?

Must first make complementary RNA.

Retrovirus genome?

Single-stranded RNA with reverse transcriptase.

Difference between lytic and lysogenic cycles?

Lytic destroys host cell; lysogenic integrates into host genome.

Phases of mitosis?

Prophase, Metaphase, Anaphase, Telophase (PMAT).

What happens during metaphase?

Chromosomes align at the cell equator.

What happens during anaphase?

Sister chromatids separate.

In which meiotic stage does crossing over occur?

Prophase I.

What is disjunction?

Separation of homologous chromosomes in Anaphase I.

What is nondisjunction?

Failure of chromosomes to separate correctly.

What phase replicates DNA?

S phase.

Main checkpoint controlled by p53?

G1 checkpoint.

What is G0?

Nondividing state.