Ch.3 Cellular Organization

Cell membrane

A selectively permeable phospholipid bilayer that regulates movement into and out of the cell.

Phospholipid bilayer orientation

Hydrophilic heads face extracellular and intracellular fluid; hydrophobic tails face inward toward one another.

Integral membrane protein

A protein embedded in the membrane, such as an ion channel.

Peripheral membrane protein

A protein located on the inner or outer surface of the membrane.

Receptor

A recognition protein that binds a specific external molecule and triggers a response inside the cell.

Ligand

A molecule that binds to and activates a receptor.

Selectively permeable membrane

A membrane that allows some substances to cross more readily than others.

What can pass through the lipid bilayer unaided, according to the slides?

Small nonpolar molecules such as oxygen and alcohol.

Active transport

Movement across a membrane that requires ATP.

Passive transport

Movement across a membrane that does not require ATP.

Concentration gradient

A difference in concentration across a space or membrane.

Diffusion

Movement of molecules or ions from higher concentration to lower concentration.

Facilitated diffusion

Passive transport of substances that cannot cross the bilayer easily, using membrane proteins; glucose is an example.

Osmosis

Diffusion of water across a membrane due to a difference in water concentration.

What happens to red blood cells in pure water, according to the slide question?

They can take in water and lyse (burst) in the hypotonic environment.

Active transport direction

Moves substances against their concentration gradient, from lower to higher concentration.

Sodium-potassium pump

Uses ATP to move 3 Na+ out of the cell and 2 K+ into the cell.

Why is the sodium-potassium pump important?

It helps maintain an electrical gradient used by nerves.

Electrical gradient

A difference in electrical charge across a space.

Endocytosis

The cell takes in material by surrounding it with membrane and pinching off an intracellular vesicle.

Phagocytosis

A type of endocytosis that takes in large particles.

Pinocytosis

A type of endocytosis that takes in fluid and dissolved substances.

Receptor-mediated endocytosis

Endocytosis that uses specific receptors to take in selected substances.

Exocytosis

Transport of material, including wastes, out of the cell by vesicles fusing with the membrane.

Cytosol

The jelly-like fluid medium where many biochemical reactions occur.

Organelle

A cell structure with a specific function, often enclosed by a membrane.

Nucleus

Contains DNA and serves as the cell's genetic control center.

Endoplasmic reticulum (ER)

A network of channels continuous with the nuclear envelope.

Ribosome

The site of protein synthesis.

Rough ER

Endoplasmic reticulum with ribosomes; involved in making proteins.

Smooth ER

Endoplasmic reticulum involved in making lipids.

Golgi apparatus

Sorts, modifies, and ships products from the rough ER.

Lysosome

Contains enzymes that break down or digest unneeded cellular components.

Mitochondrion

An energy-transforming organelle that helps convert energy from glucose into ATP.

Reactive oxygen species (ROS)

Reactive molecules that include hydroxyl radicals and hydrogen peroxide.

Oxidative stress

Cell damage caused by reactive oxygen species.

What can ROS damage?

Lipids, proteins, carbohydrates, and nucleic acids; DNA mutations may contribute to cancer.

Peroxisome

An enzyme-containing organelle that transfers hydrogen from molecules to oxygen, produces hydrogen peroxide, and helps neutralize poisons such as alcohol.

Cytoskeleton

A network that supports cell structure, motility, and division.

Microtubules

The thickest cytoskeletal elements; support against compression and help move organelles.

Microfilaments

Cytoskeletal elements that thicken the cell cortex.

Intermediate filaments

Cytoskeletal elements that help hold organelles in place.

Cilia

Structures that occur in groups and beat rhythmically.

Flagella

Long appendages used for locomotion; sperm are the only human cells with flagella.

Nucleolus

Manufactures RNA needed for ribosomes.

Nuclear pores

Openings through which ribosomal subunits exit the nucleus.

Which human cells are multinucleated, according to the slides?

Skeletal muscle cells.

Which cells have no nucleus?

Mature red blood cells.

Genome

The entire complement of an organism's DNA.

Chromatin

DNA and associated material that condenses into chromosomes during cell division.

Chromosome

A condensed structure of DNA and associated proteins, especially visible during cell division.

DNA base pairing

A pairs with T; C pairs with G.

Why is DNA complementary rather than identical across its two strands?

Each base pairs with its specific partner: A with T and C with G.

DNA replication

The process of copying DNA before cell division.

Helicase

An enzyme that untwists and separates DNA strands during replication initiation.

DNA polymerase

An enzyme that adds complementary DNA bases during replication elongation.

Semiconservative DNA replication

Each new DNA molecule contains one original strand and one newly synthesized strand.

Central dogma

DNA → RNA → protein.

Gene

A functional segment of DNA containing information to build a protein or other gene product.

Gene expression

The process of using coded genetic information to produce a gene product.

Triplet

A sequence of three DNA bases described in the slides as coding for an amino acid.

Transcription

Synthesis of mRNA from a DNA template.

mRNA

Messenger RNA that carries a copy of a gene's code from the nucleus to the cytoplasm for protein production.

Codon

A three-base sequence in mRNA that encodes an amino acid or a stop signal.

RNA polymerase

An enzyme that unwinds DNA locally and builds a complementary RNA strand during transcription.

Promoter

A DNA region that signals where transcription begins.

mRNA splicing

Processing that removes noncoding regions from pre-mRNA before it leaves the nucleus.

Spliceosome

A complex that removes introns from pre-mRNA.

Introns

Regions removed from pre-mRNA during splicing.

Exons

Regions retained in mature mRNA after splicing.

rRNA

Ribosomal RNA that contributes to the structure of ribosome subunits.

tRNA

Transfer RNA that carries an amino acid and has an anticodon matching an mRNA codon.

Anticodon

A three-base sequence on tRNA that binds to a complementary codon on mRNA.

Somatic cell

A body cell.

Diploid

Having two sets of chromosomes.

Homologous chromosome pair

Two copies of the same chromosome type in a somatic cell.

How many homologous chromosome pairs do human somatic cells have?

23 pairs.

Cell cycle

The sequence of stages through which a cell grows and divides.

G1 phase

The cell grows during interphase.

S phase

DNA replication occurs during interphase.

G2 phase

The cell prepares for division during interphase.

G0 phase

A resting or nondividing phase.

Mitosis

Division of the nucleus/genetic material into two new nuclei.

Cytokinesis

Division of the cytoplasm to form two cells.

Sister chromatids

Two copies of a chromosome that remain physically attached.

Centromere

The region that holds sister chromatids together.

Centrosome

A cell structure involved in organizing the mitotic spindle.

Mitotic spindle

A structure that helps move and separate chromosomes during cell division.

Kinetochore

A chromosome-associated structure where spindle fibers attach.

Metaphase plate

The plane at the cell's center where chromosomes line up during metaphase.

Cleavage furrow

The indentation that forms as an animal cell's cytoplasm divides.

Cell-cycle checkpoint

A control point where the cell cycle can proceed or stop.

Cyclin and cyclin-dependent kinase (CDK)

Proteins that work together to regulate progression through cell-cycle checkpoints.

How can cancer develop according to the slides?

DNA mutations or abnormalities can compromise cell-cycle control, leading to cancerous tumors.

Totipotent stem cell

Can form any cell type and an entire organism; described for the earliest embryonic cells.

Pluripotent stem cell

Can form most cell types but not an entire organism.

Multipotent stem cell

Can form any cell type within a particular cell family.

Oligopotent stem cell

Can form a few cell types within a cell family.

Unipotent stem cell

Can form one cell type.

Transcription factor

A protein that binds specific genes and promotes or inhibits transcription.