Membrane Transport and Tissues Flashcards
Phospholipid
Made up of a glycerol backbone with a phosphate group (phosphatidylcholine) and two fatty acid chains attached (for example, maybe oleic acid and palmitic acid)
Amphipathic: has polar and non polar regions
Micelle
A structure formed from phospholipids aggregating in an aqueous solution so that the polar heads are turned outward and nonpolar tails are turned inward

liposome
artificial phospholipid bilayer vesicle
formed from suspension of phospholipid molecules
Leaflets
Inner and outer layer of phospholipid bilayer membrane
Plasma membrane of Eukaryotic cell
Made up of phospholipid bilayer, contains glycolipids and steroids like cholesterol
Regulates substances that enter and leave cell as well as facilitating cell to cell communication
Glycolipids found on outer leafet only
Peripheral Proteins in Membrane
Aka extrinsic proteins
Located on surface of membrane and generally polar or hydrophilic, can’t flip sides easily
Can be ionically bonded to polar head of phospholipid or integral protein
Can contain a carbohydrate (would be a glycoprotein), carbohydrate protrude outside of cell
Integral Proteins in Membrane
Aka intrinsic proteins
Amphipathic proteins that can cross the membrane from inside of the cell to the outside
Can contain carbohydrate (making it a glycoprotein), carbohydrate protrude towards outer cell
Fluid mosaic model
Refers to the fluidity of the plasma membrane due to the ability of the phospholipids and proteins to slide past each other
Forces holding membrane together are intermolecular, parts can slide laterally, but not separate
Mosaic refers to asymmetrical layout of a membrane’s lipids and proteins
Membrane protein functions
Can act as:
- transporters: proteins select which solutes to enter and exit
- receptors: receive chemical signals from cellular environment
- attachment sites: anchor to the cytoskeleton
- identifiers: other cells can recognize
- adhesive proteins: adhesion from one cell to the next
- enzymes: control chemical reactions

Brownian Motion
The constant, irregular motion of very fine particles (such as fine dust or smoke) suspended in a fluid and observed with a microscope. Brownian motion is taken as evidence for molecules, which collide with the observed particles and cause the jitter motion.
Leads to the tendency of solutions to mixc completely with each other over time
Diffusion:
tendency of atoms, molecules, and ions in a liquid or air solution to move from areas of higher concentration to areas of lower concentration, thus becoming more evenly distributed. In general, diffusion is more rapid over shorter distances, larger concentration gradients, and higher temperatures.
Electrochemical Gradient
Combination of chemical concentration gradient and electrical gradient
Chemical concentration gradient:
Series of vectors pointing in direction of lower concentration for a solute
Electrical gradient:
Series of vectors pointing in the direction that a positively charged particle will tend to move
Membrane Permeability
Increasing polarity and size leads to decreased permeability in membrane
Large steroid hormone diffuses easily
Water diffuses slowly across membrane
Most diffusion of polar or small molecules takes place through incidental holes called leakage channels created by irregular shapes of integral proteins
Passive diffusion
Movement across the membrane through leakage channels without the assistance of membrane proteins
No ATP required, down the concentration gradient
Membrane channels
Aka carrier proteins
Proteins embedded in the cell membrane that assist molecules in moving across membrane
Facilitated Diffusion
Diffusion that occurs down the concentration gradient through membrane channels
No ATP required
Glucose transported this way
Active transport
Movement of a compound against its electrochemical gradient
Requires expenditure of energy
Primary active transport: direct use of ATP
Secondary active transport: ATP creates electrochemical gradient which is then used to acquire or expel a second molecules against its gradient
Osmotic Pressure
When concentrations of molecules on either side of membrane are not equal, a pulling pressure is generated to equal out the gradient
Water will move towards areas of higher concentration
Colligative property: based on the number of particles present rather than the type
Endocytosis
Cells acquire substances from extracellular environment by membrane surrounding the contents and allowing the entry of a vesicles to the interior of the cell
Vesicle can fuse with Golgi apparatus or targeted for destruction by lysosome
Phagocytosis
Cell membrane protrudes outward to engulf and envelop particulate matter
Triggered by binding of matter to protein receptors on cell
E.g., macrophages
Pinocytosos
Extracellular fluid is engulfed by small invaginations of cell membrane
Performed by most cells in random non-selective fashion
Receptor-mediated endocytosis
Specific uptake of macromolecules by ligand binding to receptor protein on cell membrane and then moved to a Claritin coated pit which forms a coated vesicle
Uptake of hormones or nutrients
Exocytosis
Reverse of endocytosis, where substances leave the cell in a vesicle that fuses with the cell membrane
Stages of cell cycle of typical somatic cell
First Growth phase (G1)
Synthesis (S)
Second Growth Phase (G2)
Mitosis or Meiosis (M)
Interphase: G1, S, G2
G1 of Cell Cycle
Cell grows in size, producing new organelles and proteins
RNA and protein synthesis
ER creates phospholipids and new portions of the cell membrane as secretory vesicles
Cell growth assessed at G1 checkpoint
G1 Cell Checkpoint
Assessed size of cell
If cell size is large enough (ratio of cytoplasm to DNA exceeds threshold), then cell moves to S phase, otherwise moves to G0 phase
G0 Cell Cycle Phase
Non-growing state distinct from interphase
Causes variations in cell cycle length between cells
Some cells remain in G0 permanently (neurons)
S Cell Cycle Phase
Cell focused on DNA replication, exact duplicate of each chromosome is created
Organelle and protein production slows
G2 Cell Cycle Phase
Cellular organelles duplicate
RNA and protein synthesis
10-20% of cell life cycle
G2 checkpoint at end of the G2 checks for mitosis promoting factor
G2 Cell Checkpoint
If mitosis promoting factor (MPF) is high enough, mitosis is triggered
M Cell Checkpoint
End of Mitosis, checks if chromosomes are aligned correctly score dividing
Two types of Cancer Mutations
Tumor repressor: deactivation of checkpoint protein
Oncogene: activation of a gene that causes proliferation of cell
Fibroblast
Cells that can secrete fibrous proteins such as elastin and collagen which forms a molecular network that holds cells in place
Network known as extracellular matrix
Extracellular Matrix
Molecular network that holds cells in place
Varies greatly from cell type to cell type
Can be liquid or solid
May provide structural support, determine cell shape and motility, and affect cell growth
Three classes of molecules that comprise animal cell matrices
- Glycosaminoglycans and proteoglycans Provides pliability to matrix, over 90% of matrix by mass
- Structural proteins Provide matrix with strength (collagen)
- Adhesive proteins Help individual tissues stick together
Basal lamina
Thin sheet of matrix material that separates epithelial cells from support tissue
Acts as a sieve-like barrier, selectively allowing passage of some molecules, but not others
Glycocalyx
Separates cell membrane from ECM, some animal cells contain this layer
Involved in cell-to-cell recognition, adhesion, cell surface protection, and permeability
Same material as ECM
Tight junctions
Form watertight seal from cell to cell that blocks water, ions, and other molecules from moving around and past cells
Barrier to protein movement between apical and basolateral surfaces of cell (apical side of cell faces lumen of cavity)
Desmosomes
Join two cells at a single point, strongly attached directly to cytoskeleton of cell
Do not prevent fluid from circulating around cell, but found in tissues that experience a lot of stress due to sliding (skin or intestinal epithelium)
Gap junctions
Small tunnels that connect cells, facilitate movement of small molecules and ions between cells
Cell communication with non adjacent cells
Cell sends out chemical message or hormone which can picked up receptor of other cell
If hormone small and lipophilic (steroid), can cross membrane and bind to receptor in cell (cytosol or nucleus) to change transcription
If hormone large and lipophobic (protein), binds to receptor on surface of cell which can change membrane permeability, or deactivate/activate other membrane proteins, or activates an intracellular second messenger
Intracellular second messenger
Activated as the second part of a signal cascade with a hormone binding to outside the cell possibly as first signal
cAMP, cGMP, or calmodulin
Four types of tissue
Epithelial: separates free body surfaces from surroundings
Muscle
Connective: characterized by an extensive ECM (blood, lymph, bone, cartilage, connective tissue)
Nervous
Organs
Various types of tissues work together to form
