Learn: General Biology I: Cell Structure, Function, and Signaling

What distinguishes prokaryotic cells from eukaryotic cells?

Eukaryotic cells have DNA in a nucleus; prokaryotic cells have DNA in a nucleoid.

Where is the genome of a bacterium located?

In a region of the cytoplasm called the nucleoid.

What types of organelles are found in prokaryotes?

Prokaryotes have no organelles or membrane-bound compartments.

Where is the genome of eukaryotic cells found?

In the nucleus.

What is the basic structure of the nucleus?

Spherical and bounded by two lipid bilayers. The DNA genome is inside the nucleus with all the machinery it needs to control cellular functions.

What is the nuclear envelope?

The double membrane around the nucleus made of two lipid bilayers.

What are nuclear pores?

Pores in the nuclear envelope used for transporting biomolecules.

What is the nuclear lamina made of?

Intermediate fibers that provide structural integrity to the nuclear envelope.

What are ribosomes composed of?

Proteins and rRNAs (ribosomal RNA molecules).

What is the function of a ribosome?

Synthesize proteins from amino acids following mRNA instructions.

How do free ribosomes differ from bound ribosomes?

Free ribosomes make water-soluble proteins; bound ribosomes make membrane proteins.

Where are ribosomes located in the cell?

In the cytoplasm and certain organelles.

What are the components of the endomembrane system?

Membranous compartments like Golgi apparatus, lysosomes, transport vesicles and nuclear envelope.

What is the role of the rough endoplasmic reticulum?

To make membrane proteins.

What are the functions of the smooth endoplasmic reticulum?

Processing lipids and other molecules, often for export from the cell.

What does the Golgi apparatus do?

Processes and manufactures biochemicals and traffics lipid vesicles.

What kinds of things are processed in the Golgi?

Lipids and proteins, including glycosylation for secretion.

What is the structure of the Golgi apparatus?

A stack of flattened membranous tubes and discs.

What is the role of transport vesicles?

Carry contents to other places in the cell.

What is the function of lysosomes?

Degradation of biomolecules.

How do lysosomes form and what do they contain?

Specialized vesicles containing hydrolytic enzymes.

What is the role of the central vacuole in plant cells?

Water retention to maintain turgidity.

What is the tonoplast?

The membrane surrounding the central vacuole.

What is the role of peroxisomes?

Breakdown biochemicals with hydrogen peroxide.

What are peroxisomes made from?

They are formed independently in the cytoplasm. They contain synthetic and degradatory enzymes

What are mitochondria and their function?

Powerhouse of the cell; site of cellular respiration and ATP production.

Describe the structure of a mitochondrion.

Two membranes with an intermembrane space and a matrix. Between them is the intermembrane

space, where protons are pumped during respiration. Inside the intermembrane is the matrix

where the enzymes of the Krebs Cycle are found.

Do mitochondria have a genome and ribosomes?

Yes, they have bacterial genomes and ribosomes.

What is the structure and function of chloroplasts?

Three membranes: inner, outer, and thylakoid. Chlorophyll is in thylakoid.

What kinds of cells have chloroplasts and/or mitochondria?

Only eukaryotic cells.

What are thylakoids, stroma, and grana?

Thylakoids are sites of photosynthesis where chlorophyll resides along with photosystems and where the electron transport chain is found; stroma contains enzymes for carbon fixation. Grana is thylakoid stacks, inside them is space called lumen where protons are pumped during electron transport.

Do chloroplasts have a genome and ribosomes?

Yes, they have bacterial genomes and ribosomes.

What is a cytoskeleton?

A network of fibers and filaments that provides structural support and motility to the cell.

What kinds of cells have a cytoskeleton?

All cells have a cytoskeleton, but the prokaryotic version is very different from that of eukaryotes.

What are the main roles of a cytoskeleton?

Movement of the cell, cell parts, and within the cell; structural stability; anchoring organelles.

What are the major components of the cytoskeleton?

Microtubules, actin microfilaments, intermediate filaments, all of which are fibrous protein chains.

What are microtubules and what are they made from?

Microtubules are made from tubulin protein monomers that form dimers, which then form the walls of the tubes. The 2 flavors are alpha tubulin and beta tubulin

What are the roles of microtubules?

Girders, they are key for cell motility, movement of cytoplasm, and organelles; they form spindle fibers for chromosome separation, the basal bodies and centrioles.

What is a centriole?

microtubule organizing centers key for making the mitotic spindle used to separate chromosomes during cell division.

How are centrioles related to basal bodies and flagella?

Both are made of triplets of microtubules; basal bodies are at the base of flagella, which are made of doublets of microtubules.

How are cilia and flagella related?

Both are microtubule-driven motility structures used for cellular movement.

What is the basic structure of cilia and flagella?

Microtubules in doublets in an array and covered by a membrane.

What are the roles of cilia and flagella?

Flagella act as propellers, while cilia function like oars.

What are microfilaments and what are they made of?

Microfilaments are made of actin protein.

What roles do microfilaments play in cells?

They are key for movement, forming the cleavage furrow during cell division, and driving pseudopodia for ameboid movement.

What are intermediate filaments made of and what roles do they play in cells?

Intermediate filaments are a diverse group of fibers that form the nuclear lamina and are part of desmosomes that hold cells together.

What types of cells have cell walls?

Plants, fungi, bacteria, archaea, and protists have cell walls, but not animal cells.

What are the cell walls of animal cells like?

Animal cells typically do not have formal cell walls.

What is extracellular matrix material?

A mixture of long proteins and carbohydrates that surround animal cells in tissues.

What is collagen?

A fibrous protein that is part of the extracellular matrix of animal cells.

What are glycoproteins?

Proteins with a carbohydrate component attached.

What is proteoglycan?

Mainly a fibrous carbohydrate with some protein attached, found in the extracellular matrix.

What are the main constituents of plant cell walls?

Cellulose, hemicellulose, pectins, and lignin in secondary cell walls.

What are the main constituents of bacterial cell walls?

Peptidoglycan and related molecules; some cells have an outer membrane.

Distinguish between Gram negative and Gram positive cell wall structures.

Gram-positive cells have a thick layer of peptidoglycan outside the plasma membrane; Gram-negative cells have a thin layer and an outer membrane.

What is lipopolysaccharide?

A lipid molecule with a carbohydrate component.

What are the three main types of junctions in animal tissues?

Tight junctions, desmosomes (anchoring), and gap junctions (communicating).

What are the roles and nature of desmosomes, tight junctions, and gap junctions?

Tight junctions close off spaces between cells; desmosomes anchor cells together; gap junctions are pores for molecular movement.

What did Overton contribute to our understanding of membranes?

He proposed that membranes are composed of phospholipids.

What did Langmuir contribute to our understanding of membranes?

He studied artificial membranes.

What did Gorter and Grendel contribute to our understanding of membranes?

They proposed that membranes are lipid bilayers with hydrophobic tails inside.

What did Davson and Danielli contribute to our understanding of membranes?

They proposed a wrong model of membranes with protein layers.

What did Singer and Nicholson contribute to our understanding of membranes?

They proposed the fluid mosaic model.

Describe the basic nature of cell membranes.

They consist of a lipid bilayer with hydrophobic tails inside and hydrophilic heads outside.

What are membranes composed of?

Lipids and proteins.

What kind of lipids are usually found in membranes?

Phospholipids with a negatively charged phosphate group in the head.

Why do lipids in membranes form bilayers?

Hydrophobic tails want to stay together away from water, while hydrophilic heads want to touch water.

Describe the structure of the lipid bilayer.

Lipid bilayers have hydrophobic tails inside a sandwich of hydrophilic heads.

How does the membrane act as a barrier?

Hydrophobic molecules can't easily pass the hydrophobic heads, and hydrophilic substances can't pass the hydrophobic tails.

What kinds of molecules would most likely be able to cross the membrane easily?

Small hydrophobic molecules.

Describe the salient features of the fluid mosaic model.

Lipid bilayer where lipid molecules move freely side-to-side; proteins are associated with the membrane.

How do unsaturations in lipid side chains affect the fluidity of the membrane?

Unsaturations create kinks in the side chain, preventing tight packing and increasing membrane fluidity.

What is an integral membrane protein?

A protein that is embedded in the lipid bilayer of the membrane.

What is a peripheral membrane protein?

Peripheral (extrinsic) proteins are attached to the membrane or slightly buried in the membrane.

What roles do membrane proteins play in the cell?

Membrane proteins form compartments, act as barriers for selective transport, and may have associated enzymes.

What is a transmembrane protein?

integral membrane proteins that span the lipid bilayer, often for transport or signal transduction.

What is diffusion?

Diffusion is the movement of solute molecules dissolved in a solvent.

What controls the rate of diffusion?

The rate of diffusion is controlled by thermodynamics, with solute molecules moving down the concentration gradient.

What is osmosis?

the movement of solvent (water) across a membrane to equalize solute concentrations.

What do the terms isotonic, hypotonic, and hypertonic mean?

Isotonic means equal solute concentrations; hypotonic means lower solute concentration outside the cell; hypertonic means higher solute concentration outside the cell.

How do cells react in solutions with differing tonicities?

In hypertonic solutions, cells shrink; in hypotonic solutions, cells swell and may burst.

What is facilitated diffusion and how does it work?

Facilitated diffusion is when solutes move down the concentration gradient with help from membrane transport proteins.

What performs facilitated diffusion and does it require energy?

Membrane proteins perform facilitated diffusion, using the energy of the concentration gradient, not ATP.

What are ion channels, aquaporins, and carrier proteins?

Ion channels are pores for specific solutes; aquaporins facilitate water movement; carrier proteins assist in facilitated diffusion.

Why does facilitated diffusion show saturation kinetics?

Facilitated diffusion shows saturation kinetics because all membrane proteins can become busy, limiting transport speed.

What is cotransport?

Cotransport is when two solutes move across the membrane simultaneously, often using the energy from one moving down its gradient.

What is active transport?

Active transport uses ATP energy to transport solutes across the membrane, typically against the concentration gradient.

What are uniport, symport, and antiport?

Uniport is one solute moving in one direction; symport is two or more solutes moving in the same direction; antiport is two or more solutes moving in different directions.

Describe the sodium/potassium pumps of red blood cells.

The sodium/potassium pump is an antiport system that pumps Na out and K in.

What is phagocytosis?

the process of engulfing food with membrane invaginations that form vesicles.

What is pinocytosis?

the process of engulfing liquids in a similar manner to phagocytosis.

What is exocytosis?

the secretion of materials out of a cell by vesicles fusing with the plasma membrane.

What is receptor-mediated endocytosis?

Receptor-mediated endocytosis involves specific cell surface receptors binding solutes before uptake.

What is a signal transduction pathway?

A series of events that transmit a signal from outside the cell to its interior.

What is local signaling?

occurs between cells that are physically close using chemical signal molecules.

What is long-distance signaling?

involves signal molecules moving some distance, such as through the bloodstream.

What is direct contact communication?

occurs when cell surface proteins on one cell interact with those of another.

Define ligand and receptor.

Ligands are small molecules that bind to receptors, which are typically cell surface proteins.

How do G protein-linked receptors work?

G protein-linked receptors activate G proteins with GTP when a ligand binds, initiating the signal transduction pathway.

Describe the tyrosine-kinase receptor.

Tyrosine-kinase receptors get phosphorylated on tyrosine residues and form active dimers upon ligand binding.