Chapter Four: Cell Structure and Membranes Flashcards
What is the diameter range of cells?
1-100 um in diameter
Why are cells small?
they must exchange materials with the environment and cell exchanges are limited by surface area. As cell size increases, cell volume increases more than surface area
T/F Diffusion is fast over long distances?
False
As a sphere gets larger, the surface area, volume ratio _______
decreases
What physical factors influence the rate of diffusion of each solute?
diameter of the molecules or ions, electrical charge, the temperature of the solution, concentration gradient
What are the functions of biological membranes?
boundaries, regulation, intracellular transportation, cell identification/communication/adhesion, contain & restrict some biochemical reactions
What do the proteins floating in the bilayer do?
serve as gates and pumps for substances and carry out biochemical reactions
Why do carbohydrates attach to lipids or proteins on the outer surface of the plasma membrane?
To assist with cell-cell recognition and adhesion
How do fatty acids influence a phospholipid bilayer?
They make the bilayer both flexible and fluid
What kind of interactions do lipids and proteins have, and what result does that have?
weak hydrophobic interactions causing proteins to move laterally in the bilayer; only a few of them are covalently attached to membrane lipids
T/F Membranes can’t flip from one side of the bilayer to the other
F; They can, its just very rare
What is the degree of membrane fluidity influenced by
lipid composition, temperature
short, unsaturated chains ______ fluidity
increases
_______ alters interactions among fatty acid side chains
cholesterol
fluidity ______ in cold conditions
decreases
How will two different proteins distribute in a membrane?
They will fully intermix into an equilibrium
Cell membranes have _____ permeability
selective
Passive transport
movement by diffusion; no outside energy required; concentration gradient is the driving force (simple and facilitated diffusion)
simple diffusion
directly across the phospholipid bilayer
facilitated diffusion
across a membrane via channel or carrier proteins
Active transport
movement against a concentration gradient; via a protein pump that requires energy to operate
What is diffusion?
the net movement from regions of greater concentration to regions of lesser concentration until equilibrium is reached
Which molecules undergo simple diffusion?
O2, CO2, and a small, nonpolar, lipid-soluble molecules can cross the membrane unaided
At what rate do steroid molecules, small hydrophilic proteins, and large hydrophilic molecules move through the membrane is simple diffusion?
steroid molecules – rapidly
a small protein – slower
large molecule – very slow
Carrier proteins
membrane proteins that function as channels that must bind the transported solutes to speed their diffusion through the bilayer
What does the rate of carrier proteins depend on?
concentration gradient
What allows for a much faster diffusion of glucose?
Carrier proteins in facilitated diffusion
Channel Proteins
integral membrane proteins form a central pore lined with polar amino acids; solute streams down the gradient
What do Gated Ion Channels do?
They open to allow ion passage; the gate opens when protein is stimulated to change shape
T/F Each ion channel exists specifically for different ions
True
T/F Cells have a balance of ions inside and out
F; There are more positively charged ions outside of the membrane and more negatively charged ions inside the membrane
What is Osmosis?
diffusion of water across a membrane that the solutes cannot pass through
Does osmosis depend on the number of solute particles present of the type of particles?
number of solute particles
In what direction will water molecules diffuse?
from the region of higher water concentration (and lower solute concentration) to the region of lower water concentration (higher solute concentration)
Osmotic pressure
the pressure that must be applied to a solution to prevent the flow of water across a membrane by osmosis
What is osmolarity?
solute particles per liter of water
Osmotic pressure can be quantified by ____
osmolarity
What is tonicity?
the relative concentration of solutes on either side of a membrane; determines the direction and extent of net water movement
What does tonicity determine?
determines direction and extent of net water movement
Isotonic solutions
Have equal solute concentrations
Hypotonic solution
Has a lower solute concentration
Hypertonic solution
has a higher solute concentration
When there is a net flow of water, it occurs from the _____ to the ______ solution
hypotonic to the hypertonic
What are the two ways water can cross a membrane?
directly or by hitchhiking with hydrated ions (which is slow and not efficient
Primary active transport
energy comes from direct hydrolysis of ATP
Secondary active transport
Energy comes from an ion concentration gradient that is established by primary active transport
What does the Na+ K+ Pump do? Why is it important?
Pumps Na+ out of the cell and K+ into the cell, both against the gradient. It maintains membrane potential and stabilizes cell volume
What energy source does the Na+ K+ Pump use
energy of ATP directly (primary active transport)
What does the Glucose-Na+ transporter do?
Transports glucose across the membrane against its gradient; Works in parallel to the Na+ - K+, which provides the energy through the movement of Na+
Macromolecules cross the membrane through _________
membrane vesicles
Endocytosis
plasma membrane surrounds the extracellular material and invaginates, forming a vesicle
Exocytosis
material in vesicles is expelled (secreted) from a cell by fusion with the plasma memebrane
Endocytosis
material in vesicles is expelled (secreted) from a cell by fusion with the plasma membrane
How does exocytosis occur?
A vesicle fuses with the cell membrane. The contents of the vesicle are released, and its membrane becomes part of the cell membrane
How does endocytosis occur?
The cell membrane surrounds a part of the exterior environment and buds off as an internal vesicle
What is the function of the cytoskeleton?
supports and maintains cell shape, holds organelles in position, moves organelles in cytoplasm, interacts with extracellular structures to hold cell in place
What three filaments composes the cytoskeleton?
microfilament, intermediate filaments, microtubules
What is the function of microfilaments?
Helps a cell or parts of a cell to move, determines cell shape
What is the structure of a microfilament? It’s motor protein?
Made from actin, which has positive and negative ends and polymerizes to form long helical chains; motor protein myosin
What is the function of microtubules?
they form a rigid internal skeleton in some cells, they act as a framework for motor proteins
What is the structure of microtubules?
made from tubulin (a dimer), has positive and negative ends and can change length rapidly by adding or losing dimers
What are motor protiens?
They undergo reversible shape changes powered by ATP hydrolysis
Kinesin motors
move from minus end to plus end
Dynein motors
move from plus end to minus
Cilia
short, usually many present, move with stiff power stroke and flexible recovery stroke
Flagella
longer than cilia, usually one or two are present, movement is snakelike
What is the function of cell walls?
Provide structural support, and protection from physical damage and pathogens
Which cells build cell walls?
plants, archaea, bacteria, fungi, some protists
What are cell walls made of?
cellulose, chitin, or protiens
What connects adjacent plant cells?
plasma membrane-lined channels called plasmodesmata
Extracellular matrix
Made of collagen adn gel-like proteoglycans, present in animal cells
What are the functions of extracellular matrix?
holds cells together in tissues; helps filter materials, helps orient cell movements during embryonic development and tissue repair
What does integrin bind to?
the matrix outside epithelia cells and to actin filaments inside the cells; this binding is noncovalent and reversible
Tight junction
cell adhesion and sealing; form a “quilted” seal that excludes the movement of dissolved materials through the space between epithelial cells
Desmosomes
cell adhesion without sealing; link adjacent cells tightly, but permit materials to move around them in the intracellular space
Gap Junctions
cell adhesion and molecules moving between cells; let adjacent cells communicate
What structural features do all cells have?
plasma membrane, cytoplasm, genome of DNA, ribosomes
plasma membrane
surrounds the fluids and other structures that make up the insides of a cell
cytoplasm
the insides, which consists of a liquid water-based cytosol containing dissolved molecules as well as various visibles structures
ribosomes
molecular machienes for making cell protiens
Prokaryotic cells
bacteria and archaea; genomes consisting of one or two molecules of DNA concentrated in a nucleoid
Which has greater metabolic diversity, prokaryotic cells or eukaryotic cells?
prokaryotic
_______ cells have variable features
prokaryotic
______ lack a nucleus and membrane-enclosed internal compartments
prokaryotes
What organisms are made of eukaryotic cells?
protists, fungi, plants, animals
Characteristics of eukaryotic cells
larger and more complex than prokaryotes, have membrane-enclosed compartments (organelles) which each have a specific role, separation of cellular activities and specialization of eukaryotic cells
Eukaryotic Cell Organization
Cell = plasma membrane + cytoplasm + nucleus
Cytoplasm = cytosol + organelles + cytoskeleton
What are the main parts of an animal cell
Centrioles, Cilia
What are the main parts of plant cells
Cell wall, Plasmodesmata, Chloroplasts, Central Vacuoles
Nucelus
Large, dense, visible with a light microscope; houses the nucleolus as well as DNA
Nuclear envelope
two membranes perforated by nuclear pores that regulate movement of substances
Nucleolus
where ribosomes are made
Endomembrane System
An interconnected system of membranes that includes the nuclear envelope, endoplasmic reticulum, Golgi lysosomes, and plasma membrane
In the endomembrane system, tiny ___________ shuttle substances between various components
vesicles shuttle substances
Endomembrane System
specialized for the manufacture, customization, packaging, and shipping of cellular macromolecules, especially proteins
Rough ER (RER)
contains many ribosomes for the manufacture of proteins that will be part of endomembrane system or exported
Smooth ER (SER)
site of protein modification, glycogen and lipid synthesis, chemical detox
The Golgi (apparatus)
flattened sacs of membranes that receives, modifies nad packages proteins from RER; manufacture of cell wall polysaccharides (plant cells)
Primary Lysosomes
originate from Golgi; hydrolases break down macromolecules
Secondary Lysosomes
vesicle formed by phagocytosis that has fused with a primary lysosome
Mitochondria
Site of the chemical reactions of cellular respiration that supply much of cellular energy
The greater the energy demands of a cell, the _____ mitochondria it will have
more
Where is food transformed into ATP
mitochondria
Chloroplasts
site of chemical reactions of photosynthesis
Where is light energy converted to chemical energy
Thylakoid membranes plus two membranes
Where are carbohydrates synthesized?
stroma
Central Vacuoles
large, fluid-filled organelles, store dissolved waste products and toxic compounds, provide structure for plant cells – water entered the vacuoles by osmosis, creating turgor pressure
Cell wall
made of cellulose fibers embedded in other complex polysaccharides and proteins; functions as a barrier, gives cell shape and support
