The Cell

What are all organisms composed of?

Cells.

How many cells roughly compose the human body?

Roughly 1x10^4 cells

Are human cells specialized?

Yes, human cells are highly specialized.

Into what two principal categories are all human cells divided?

Sex cells and somatic cells.

What are the male sex cells?

Sperm.

What are the female sex cells?

Oocytes.

What is the definition of somatic cells?

All the other cells in the body that are not sex cells.

How many copies of each chromosome do mature sex cells carry?

Only one copy.

What are two alternative terms for the plasmalemma?

Cell membrane and plasma membrane.

What is the plasmalemma?

The exterior membrane of the cell.

What is the cytoplasm?

Everything contained within the plasmalemma.

What are the two major divisions of cytoplasm?

Cytosol and organelles.

Into what two categories are organelles divided?

Nonmembranous organelles and membranous organelles.

Which six nonmembranous organelles are found in the cell?

Cytoskeleton, microvilli, centrioles, cilia, flagella, and ribosomes.

Which six membranous organelles are found in the cell?

Mitochondria, nucleus, endoplasmic reticulum, Golgi apparatus, lysosomes, and peroxisomes.

What is the structural composition of the plasmalemma?

Phospholipid bilayer.

What are the four major functions of the plasmalemma?

Physical isolation, sensitivity, structural support, and regulation of exchange with the environment.

What three passive transport mechanisms occur across the plasmalemma?

Diffusion, osmosis, and facilitated diffusion.

What three active transport mechanisms occur across the plasmalemma?

Active transport, endocytosis, and exocytosis.

What determines the direction of diffusion?

Relative concentrations of solutes.

What factors affect the rate of diffusion?

Size of gradient, molecular size, charge, lipid/protein solubility, and temperature.

What substances move across the plasmalemma via simple diffusion?

Small inorganic ions and lipid-soluble materials.

What is osmosis?

Movement of water (solvent) molecules toward high solute concentrations across a membrane.

What factors affect the rate of osmosis?

Concentration gradient and opposing pressure.

What substance moves across the cell membrane specifically via osmosis?

Water only.

What is facilitated diffusion?

Transport of materials down a concentration gradient using carrier molecules across a membrane.

What factors affect the rate of facilitated diffusion?

Size of gradient, molecular size, charge, solubility, temperature, and availability of carrier protein.

What substances cross the cell membrane via facilitated diffusion?

Glucose and amino acids.

What is active transport?

Movement of materials against opposing concentration gradients using carrier molecules and ATP.

What factors affect the rate of active transport?

Availability of carrier, substrate, and ATP.

Which specific ions are transported across the plasmalemma by active transport?

$ ext{Na}^+$, $ ext{K}^+$, $ ext{Ca}^{2+}$, and $ ext{Mg}^{2+}$.

What is endocytosis?

Formation of membranous vesicles (endosomes) containing fluid or solid material at the plasmalemma.

What energy source is required for endocytosis?

ATP.

What substances are taken into all cells via endocytosis?

Fluids and nutrients.

What substances are taken into specialized cells via endocytosis?

Debris and pathogens.

What is exocytosis?

Fusion of vesicles containing fluids and/or solids with the plasmalemma.

What two components are required for exocytosis to occur?

ATP and calcium ions.

What substances are released from cells via exocytosis?

Fluid and wastes.

Which molecules can diffuse directly across the lipid bilayer of the plasmalemma?

Lipids, lipid-soluble molecules, and soluble gases ($ ext{O}_2$ and $ ext{CO}_2$).

Which molecules diffuse through membrane channels in the plasmalemma?

Water, small water-soluble molecules, and ions.

How do large molecules cross the plasmalemma if they cannot fit through channels or diffuse through lipids?

Transported by a carrier mechanism.

How does the protein concentration of cytoplasm compare to extracellular fluid?

Cytoplasm is very high in protein and has more proteins than extracellular fluid.

What percentage of total cell weight is accounted for by proteins?

$15 ext{--}30 ext{\%}$.

What is contained within the cytosol?

Dissolved nutrients, ions, soluble and insoluble proteins, and waste products.

What separates the cytosol from extracellular fluid?

Plasmalemma.

What is cytosol principally composed of?

Water.

What acts as the intracellular solvent for all cellular components?

Cytosol.

Which ion is found in high concentration in cytosol?

Potassium ($ ext{K}^+$).

Which ion is found in high concentration in extracellular fluid?

Sodium ($ ext{Na}^+$).

What organic nutrients are dissolved in the cytosol?

Amino acids, lipids, and carbohydrates.

Is cytosol cell-type specific?

Yes.

What is the definition of organelles?

Intracellular structures that perform specific functions.

What three areas do organelle functions support?

Normal cell structure, maintenance, and/or metabolism.

What defines a nonmembranous organelle?

An organelle that is always in contact with the cytosol.

What is the cytoskeleton?

The internal protein framework that gives cytoplasm strength and flexibility.

What are the four major components of the cytoskeleton?

Microfilaments, intermediate filaments, thick filaments, and microtubules.

What protein forms microfilaments?

Actin.

What are the three functions of microfilaments?

Anchor cytoskeleton to integral proteins, stabilize position of membrane proteins, and anchor plasmalemma to cytoplasm.

What microfilament structure lies just beneath the plasmalemma?

Terminal web.

What protein is given as an example of an intermediate filament?

Keratin.

What are the three functions of intermediate filaments?

Provide strength, stabilize organelle position, and transport material within cytosol.

What protein polymerizes to form microtubules?

Tubulin.

What is the primary component of the cytoskeleton?

Microtubules.

What are three functions of microtubules?

Control cell shape, aid in cell division, and aid in cell movement.

Which three structures are composed of microtubules?

Centrioles, cilia, and flagella.

What is the microtubule arrangement of a centriole?

Nine microtubule triplets ($9+0$ array).

What does a centrosome contain?

A pair of centrioles oriented at right angles to one another.

What is the microtubule arrangement of a cilium?

Nine pairs of microtubules surrounding a central pair ($9+2$ array).

What structure anchors a cilium to the cell?

Basal body.

Describe the stiffness of a cilium during its power stroke vs. return stroke.

Relatively stiff during power stroke; bends and moves parallel to cell surface during return stroke.

What is the approximate diameter of a ribosome?

$ ext{approx } 25 ext{ nm}$.

Where are free ribosomes located?

Free in the cytoplasm.

Where are fixed ribosomes located?

Attached to the endoplasmic reticulum.

What two subunits compose an individual ribosome?

Small ribosomal subunit and large ribosomal subunit.

What chemical components form ribosomes?

RNA and proteins.

What defines a membranous organelle?

An organelle surrounded by a phospholipid bilayer membrane.

Describe the membrane structure of mitochondria.

Double membrane consisting of an outer membrane and an inner membrane folded into cristae.

What are cristae?

Folds of the inner mitochondrial membrane.

What is the mitochondrial matrix?

Inner network of enzymes and source for cellular energy production.

What percentage of cellular ATP is produced by mitochondria?

$95 ext{ %}$.

What is the primary function of the nucleus?

Storage site of genetic material.

What structure surrounds the nucleus?

Nuclear envelope (double membrane).

What is the function of nuclear pores?

Allow passage of relatively large proteins and nucleic acids in and out of the nucleus.

What molecular weight size limit passes through nuclear pores?

$ ext{MW} < 44 ext{ kDa}$.

What is the nucleolus?

Dense region in nucleoplasm that is the site of rRNA synthesis and assembly of ribosomal subunits.

What is the endoplasmic reticulum?

Network of intracellular membranes forming hollow tubes, flattened sheets, and rounded chambers (cisternae).

What are cisternae in the endoplasmic reticulum?

Hollow tubes, flattened sheets, and rounded chambers.

What six functions are performed by the Endoplasmic Reticulum?

Synthesize carbohydrates/steroids/lipids, assemble/modify translated polypeptides, store absorbed substances, transport key molecules, and inactivate cellular toxins.

How do Rough ER and Smooth ER differ structurally?

Rough ER has ribosomes bound to membranes; Smooth ER lacks attached ribosomes.

What is the function of Rough ER?

Modification and packaging of newly synthesized proteins.

What are the functions of Smooth ER?

Lipid, steroid, and carbohydrate synthesis, and calcium ion storage.

What is the structure of the Golgi apparatus?

Stacks of flattened membrane discs called cisternae.

What are the three main functions of the Golgi apparatus?

Synthesis and packaging of secretions, packaging special cytosolic enzymes, and renewal or modification of the plasmalemma.

What is the forming face of the Golgi apparatus called?

Cis face.

What is the maturing face of the Golgi apparatus called?

Trans face.

Where do transport vesicles enter the Golgi apparatus?

Forming (cis) face.

What three types of vesicles leave the Golgi apparatus from the trans face?

Secretory vesicles, membrane renewal vesicles, and lysosomes.

What are lysosomes?

Vesicles containing digestive enzymes packaged by the Golgi apparatus.

How is a secondary lysosome formed in organelle recycling?

Primary lysosome fuses with the membrane of another organelle, such as a mitochondrion.

How is a secondary lysosome formed during endocytosis?

Primary lysosome fuses with a vesicle containing fluid or solid materials from outside the cell.