Cell Biology Pre-Matriculation Review

58 question-and-answer flashcards covering major concepts from the Cell Biology pre-matriculation review, including cellular components, metabolism, gene expression, signaling, cytoskeleton, organelles, and cell-cycle regulation.

What are the four major molecular components found inside a cell?

Proteins, carbohydrates, lipids, and nucleic acids.

What substance constitutes roughly 70 % of the intracellular space?

Water.

Which organelle houses DNA and initiates transcription in eukaryotic cells?

The nucleus.

What structure separates nuclear DNA from the protein-translation machinery in the cytoplasm?

The nuclear envelope.

Which energy-producing process occurs in mitochondria and is more efficient than anaerobic pathways?

Oxidative phosphorylation.

What property of the plasma membrane permits selective passage of molecules?

It is semipermeable.

Name two small, energy-rich molecules that store cellular energy for later use.

ATP and NADH.

List the three metabolic processes that generate energy when oxygen is present in eukaryotes.

Glycolysis, the citric acid cycle, and oxidative phosphorylation.

What class of proteins lowers activation energy to speed up biochemical reactions?

Enzymes.

What term describes the inhibition of an early enzymatic step by the pathway’s end product?

Feedback inhibition.

How do the two DNA strands interact to maintain the helix?

Complementary base pairing (A with T, G with C).

During transcription, is RNA copied from both DNA strands?

No; RNA is single-stranded and transcribed from only one DNA strand.

Which class of RNA is translated into protein?

Messenger RNA (mRNA).

What proteins package DNA into nucleosomes?

Histones.

Which chromatin region—euchromatin or heterochromatin—contains actively transcribed genes?

Euchromatin.

What modification converts a primary RNA transcript into mature mRNA?

RNA splicing (removal of introns, joining of exons).

Are all genes expressed simultaneously in every cell type?

No; gene expression varies with time and cell type.

What building blocks of proteins are carried by tRNAs?

Amino acids.

Which protein structural level features α-helices and β-sheets?

Secondary structure.

What is the structural function of microtubules and actin filaments?

They provide shape and support to cells.

Which proteins catalyze metabolic reactions and can modify other proteins’ activity?

Enzymes.

Name the three components of a glycerophospholipid.

Glycerol backbone, phosphate group, and fatty-acid chains.

List the three major cytoskeletal elements in eukaryotic cells.

Microtubules, actin filaments, and intermediate filaments.

Give one membrane-bound component NOT part of the endomembrane system.

Mitochondrion (or chloroplast).

Briefly describe how ER-synthesized proteins reach their destinations.

Signal sequences route them into vesicles that move along microtubules from ER to Golgi and onward; vesicles fuse with target membranes, then recycle back.

Where are the cis-Golgi and trans-Golgi located relative to the ER?

Cis-Golgi faces and receives vesicles from the ER; trans-Golgi lies farthest from the ER and sorts cargo for final delivery.

Which organelle is rich in hydrolases and digests macromolecules?

Lysosome.

Mitochondria are considered the __ of the cell because they generate large amounts of ATP.

Powerhouse (or power plant).

Give two unique structural/functional features of mitochondria.

They have a double membrane and possess their own genome.

The electron-transport chain creates what gradient used by ATP synthase?

A proton (H⁺) gradient across the inner mitochondrial membrane.

True or False: Most mitochondrial proteins are encoded by mitochondrial DNA.

False; most are encoded by nuclear genes and imported into mitochondria.

Name the three main classes of cell-surface receptors.

G-protein-coupled receptors (GPCRs), ion channel receptors, and enzyme-linked receptors (e.g., receptor tyrosine kinases).

What are second messengers?

Small molecules that initiate and coordinate intracellular signaling pathways after receptor activation.

List three common second messengers and the enzymes that generate them.

cAMP (adenylate cyclase), DAG & IP₃ (phospholipase C), Ca²⁺ (released from stores, often triggered by IP₃).

Define G proteins.

GTP- or GDP-binding proteins that act as molecular switches (active when GTP-bound, inactive when GDP-bound).

What distinguishes heterotrimeric G proteins?

They contain α, β, and γ subunits; α and γ are membrane-anchored.

What structural feature characterizes GPCRs?

Seven transmembrane domains with external ligand site and intracellular G-protein-binding domain.

Summarize the sequence of GPCR-mediated signaling.

Ligand activates GPCR → GPCR activates heterotrimeric G protein → GDP on α is replaced by GTP → α and βγ separate and regulate target enzymes/ion channels → second messengers produced.

Which excitable cell types rely heavily on ion channels?

Neurons, muscle cells, and sensory receptor cells.

How do ion channels generate rapid cellular responses?

They open/close quickly, allowing ions to flow and create electrical signals that propagate faster than diffusion-based chemical signals.

Name three general cellular processes controlled by receptor tyrosine kinases (RTKs).

Cell growth, differentiation, and survival.

What ligands typically activate RTKs?

Growth factors, hormones, certain ECM proteins, and cell-surface proteins like ephrins.

How do RTKs differ structurally from other surface receptors?

They possess intrinsic enzyme (tyrosine kinase) activity.

Explain RTK activation.

Ligand binding causes receptor dimerization and cross-phosphorylation, triggering downstream signaling cascades that alter gene transcription.

Give two side-to-side cellular junctions affecting signaling.

Gap junctions and desmosomes (others: adherens junctions, integrin connections).

What are gap junctions and how do they aid signaling?

Intercellular pores that permit ions and small molecules to pass, enabling electrical and metabolic coupling between cells.

Define integrins and their role in signaling.

Transmembrane αβ proteins linking actin cytoskeleton to ECM or neighboring cells; their dynamic attachments influence cytoskeleton and intracellular signaling.

List, in order, the three phases of interphase in the eukaryotic cell cycle.

G₁, S, and G₂ phases.

During which interphase stage does DNA replicate?

S phase.

How do cyclin-dependent kinases (CDKs) regulate the cell cycle?

By phosphorylating substrate proteins essential for progression, such as condensins and lamins.

Do individual cyclins bind the same CDK throughout the cell cycle?

No; specific cyclins associate with particular CDKs only at defined stages.

Are cyclin levels constant across the cell cycle?

No; cyclins are synthesized as needed and degraded at specific times.

Name, in order, the five phases of mitosis.

Prophase, prometaphase, metaphase, anaphase, and telophase.

During which mitotic phase do sister chromatids align at the cell equator?

Metaphase.

What is the physical process that partitions the parent cell into two daughters?

Cytokinesis.

What is the process by which stem cells divide to yield one differentiated cell and one stem cell?

Asymmetric cell division.

What normal role of p53 is lost when both gene copies are mutated in cancer?

p53 normally senses DNA damage and activates transcription of checkpoint control genes to halt the cycle or induce apoptosis.