Cytology and Cell Transport Flashcards

A complete set of vocabulary flashcards covering cell theory, plasma membrane structure, cell junctions, and passive and active transport mechanisms directly from the lecture transcript.

Cell theory

• A cell is the structural and functional unit of life 

• All living organisms are composed of one or more cells

• All cells arise from pre-existing cells -> cell division

Cell diversity

• Over 200 different types of human cells

• Types differ in size, shape, and subcellular components; these differences lead to  differences in functions

Cell function

• How well the entire organism functions depends on individual and combined activities of all of its cells

• Structure and function are complementary (depend on eachother)

• Biochemical functions of cells are dictated by shape of cell and specific subcellular structures

Human cells have three basic parts:

1.   Pasma membrane: flexible outerbody

2.   Cytoplasm: intercellular fluid containing organelles

3.  Nucleus: DNA-containing control center (chromosomes)

The plasma membrane

• Acts as an active barrier separating intercellular fluid (ICF) from extracellular fluid (ECF) “outside”

 plasma membrane

• Is the “contact” surface so it provides:

  • a)  cell adhesion- to either other cells or a surface

  • b) cell identity markers

  • c) receptors- for various chemicals

The plasma membrane structure

• Consists of membrane lipids  that form a flexible lipid bilayer

• Specialized membrane proteins float through this fluid membrane, resulting in constantly changing patterns

fluid mosaic model

• semi-fluid bi-layer of phospholipids arranged and held together by their relationship with water (polar heads on surface, non polar tails inside)

• Polar + glycerol and phosphate heads; nonpolar: fatty acids

Membrane proteins:

• Allow cell communication with environment

• Make up about half the mass of plasma membrane 

• Most have specialized membrane functions

• Some float freely, and some are tethered to intracellular structures

Membrane proteins two types:

• Integral proteins

• peripheral proteins

Integral proteins

• Firmly inserted into membrane 

•  Most are transmembrane proteins (span membrane)

• Have both hydrophobic and hydrophilic regions

  • Hydrophobic areas interact with lipid tails

  • Hydrophilic areas interact with water

• Function as:

  •  Transport proteins (channels and carriers)

  •  Enzymes

  •  receptors

Peripheral proteins

• Loosely attached to integral proteins 

• Include filaments on intracellular surface used for plasma membrane support

• Function as:

  • Enzymes

  •  Motor proteins for shape change during cell division and muscle contraction

  •  Cell-to-cell connections

  • Part of glycocalyx, serving as identification markers for cell recognition

Cell junctions:

• Some cells are “free” (not bound to any other cells)

  • Examples: blood cells, sperm cells

• Most cells are bound together to form tissues and organs

• Three ways cells can be bound to each other

•  Tight junctions

• Desmosomes

•  Gap junctions

Membrane transport

• Plasma membranes are Selectively permeable

  • Some molecules pass through easily; some do not

• Two ways substances cross membranes

• Passive processes: no energy required can pass on through

• Active processes: energy is needed to be pumped into cell or out of cell

Passive transport:

• Passive transport requires no energy

•  Occurs down a concentration/pressure gradient

  •  Moves from an area of high to low

Two types of passive transport

Diffusion

• 1) Simple diffusion

• 2) Facilitated diffusion - help

• 3) Osmosis - diffusion of H2O

Simple diffusion

• Hydrophobic substances diffuse directly through the phospholipid bilayer

• Examples:

  • Oxygen

  • Carbon dioxide

  • Fat-soluble vitamins

• 2) Facilitated diffusion

Certain hydrophilic (e.g., glucose, amino acids, and ions) are transported passively down their concentration gradient by:

• Carrier -mediated facilitated diffusion

• Carriers transport specific polar molecules, such as sugars and amino acids, that are too large for membrane channels

  • Example of specificity: glucose carriers will carry only glucose molecules, nothing else

• Binding of molecule causes carrier to change shape, moving molecule in process

• Binding is limited by number of carriers present

  • Carriers are saturated when all are bound to molecules and are busy transporting

•  Channel -mediated facilitated diffusion

• Channels with aqueous- filled cores are formed by transmembrane proteins 

• Channels allow for transport molecules such as ions or water (osmosis) down their concentration gradient 

  • Specificity based on pore size and/or charge

  • Water channels are called aquaporins - water pore

the two types of Channel -mediated facilitated diffusion

• Leakage channels

  • Always open

•  Gated channels

  • Controlled by chemical or electrical signals

Osmosis

•  Movement of solvent, such as water across a selectively permeable membrane

• Water diffuses through plasma membranes

• Water concentration varies with number of solute particles because solute particles displace water molecules

  • When solute concentration goes up, water concentration goes down, and vice versa

• Flow occurs when water (or other solvent) concentration is different on the two sides of a membrane

  • Water diffuses from areas of Low solute (high water)  concentration to areas of High solute (low water) concentration

Tonicity

• Ability of a solution to change the shape or tone of cells by altering the cells’ internal water volume 

• Isotonic solution

• Isotonic solution has same osmolarity as inside the cell, so volume remains unchanged

• Hypertonic solution

• Hypertonic solution has a higher solute and lower solvent concentration than the cell, so water flows out of cell, resulting in cell shrinking

  • Shrinking is referred to as crenation

• Hypotonic solution

• Hypotonic solution has lower solute concentration and higher solvent concentration, so water flows into cell, resulting in cell swelling

  • Can lead to cell bursting, referred to as lysing

Active transport:

•  Moves solutes against their concentration gradient (from low to high)

• Requires ATP (energy) to move solutes across a plasma membrane for any of these reasons:

  • Solute is too large for channels, or

  • Solute is not lipid soluble, or

  • Solute is not able to move down concentration gradient

1) primary active transport

• Shape change causes solutes (ions) bound to protein to be pumped across membrane

  •  Moves against concentration gradient

  • Resembles a revolving door

  • Example of pumps: calcium, hydrogen (proton), Na⁺-K⁺ pumps

2) Secondary active transport

• Depends on ion gradient that was created by primary active transport system

•  Energy stored in gradients is used indirectly to drive transport of other solutes
  
  

• Low Na⁺ concentration that is maintained inside cell by Na⁺-K⁺ pump strengthens sodium’s drive to want to enter cell

• Na⁺ can drag other molecules with it as it flows into cell through carrier proteins in membrane

  • Some sugars, amino acids, and ions are usually transported into cells via secondary active transport

Vesicular active  transport (requires energy)

2 types

• Endocytosis

• Exocytosis

Endocytosis

• Cell membrane surrounds something and pinches off, bringing it into the cell

• Phagocytosis – solids: “cell eating”

• Pinocytosis – liquids: “cell drinking”

Exocytosis

• Vesicle merges with plasma membrane and transports substance out of the cell

• Substance being ejection is enclosed in a Secretory vesicle - vessel

  • Secretion of hormones, waste, mucus, etc.