Cells- Anatomy

Slide Set 3

Cytology

• The study of cells

Sex cells

germ cells or reproductive cells

(sperm + oocyte)

Somatic cells

Everything else

• if it is not a sperm or egg cell

Plasma Membrane

• acts as a barrier to separate what inside and what outside the cell

Phospholipid bilayer

• containing proteins, cholesterol, and glycolipids

• separates intracellular fluid (ICF) from extracellularr fluid (ECF)

  • Interstitial fluid (IF) is the ECF that directly surround most sells

Ion distribution differs across the membrane

ECF → high Na + and low K+

ICF → low Na + and high K+

The membrane its selectively permeable

• regulates which substances enter and leave the cell

Membrane Lipids

• Phospholipids (around 75%)

• Glycolipids ( around 5%)

• Cholesterol (around 20%)

Phospholipids (75%)

• Form the basic lipid bilayer

• Hydrophilic heads face the fluid

• Hydrophobic tails face inward

Glycolipids (5%)

• Glyco= think of carbs

• Lipids with carbohydrate chains extending from extracellular surface

• Important for cell recognition

• Example: some blood group antigens on RBCs (A, B, and O)

Cholesterol (20%)

• Located between phospholipids

• Helps stabilize the membrane by regulating fluidity

• Limits excessive phospholipid movement at higher temperatures

  • Prevents phospholipids from packing too tightly at lower temperatures

• Cholesterol is hydrophobic, will mined itself in the hydrophobic enviorment

Functions of Membrane Proteins - Transport proteins

Move substances across the plasma membrane

• Examples: ion channels, sodium- potassium pump

Receptors

• bind chemical signals and trigger a cellular response

  • Example: acetylcholine receptors on skeletal muscle cells

Attachment proteins

• anchor cells to the cytoskeleton or extracellular structures

  • Example: hemidesmosomes attach epithelieal cells to the basement membrane

Enzymes

Speed up chemical reactions at the membrane

• example: digestive enzymes on intestinal epithelial cells

Intercellular joining

connect neighboring cells

• Example: tight junctions, desmosomes, gap junctions, other adhesion molecules

Recognition proteins

• help cells identify and distinguish one another

• Example: MHC (Major histocompatibility complex) help immune cells recognize the body’s own cells, glycoproteins of red blood cells

Integral proteins

embedded within the phospholipid bilayer

• Many extend completely across the membrane and are called transmembrane proteins

• Hydrophobic regions interact with phospholipid tails

• Hydrophilic regions are exposed to the ICF and / or ECF

• Examples

  • ion channels

  • transporters

  • Receptors

  • some enzymes

Peripheral proteins

These do not stand the whole membrane

• loosely attached to the inner or outer surface of the membrane

• Do no extend into the hydrophobic interior of the bilayer

• Often attach to integral proteins or phospholipid heads

• Examples

  • Cytoskeletal proteins

  • Some enzymes

Six functions of membrane Proteins

1. Transport

2. Receptors for signal transduction

3. Attachment to cytoskeleton and basement membrane (basal lamina)

4. Enzymatic activity

5. Intercellular joining

6. Cell-cell recognition

Transport

• Channel/pore

• a protein that spans the membrane may provide a hydrophilic channel across the membrane that is selective for a particular solute ( left )

• Some transport proteins hydrolyze ATP as an energy source to actively pump substances across the membrane (right)

In general:

• allows rings to by pass the membrane that can’t do but on their own

Receptors for signal transduction

• A membrane protein exposed to the outside of the cell may have a binding site that firs the shape of a specific chemical messenger, such as a hormone

• When bound, the chemical messenger may cause a change in shape in the protein that initiates a chain of chemical reactions in the cell

In general:

• when a receptor of activated, some type of signal (ligand) transduction will occur immediately

• Ligand will only respond to respective receptor

Attachment to cytoskeleton and basement membrane (basal lamina)

Hemidesmosome- desmosome that holds on to the basement membrane

Enzymatic activty

• A membrane protein may be an enzyme with its active site exposed to substances in the adjacent solution

• A team of several enzymes in a membrane may catalyze sequential steps of a metabolic pathway as indicated (left to right) here

Intercellular joining

• attaches different types if cells interacting with each other

• White blood cells (leukocytes) joining together to fight off infection

Intercellular joining part 2

• Allow adjacent cells to attach

  • Common in epithelial cells

  • Limit fluids and most molecules from moving between cells

  • Tight junctions

  • Desmosomes

Tight Junctions

• seal to prevent passage between cells (less strong)

• Urinary bladder

• like glue, easy to rip apart

Desmosomes

• anchor for mechanical strength

• Skin

• keeps strong connection

  • Hemidesmosome- type of desmosome

Gap Junction

• directly connects the cytoplasm of two neighboring animal cells, allowing ions, water, and small molecules to pass freely between them.

Cell-cell recognition

• some glycoproteins (proteins bonded to short chains of sugars) serve as identification tags that are specifically recognized by other cells

• Blood types are a identification type fir this

  • Example

    • - allow the immune system to recognize our cells as our own

Moving in and out of the cell (part 1)

• Passive Transport (no energy)

• No cellular energy (ATP) is required

• Substances move down their concentration gradient from HIGH to LOW concentration

• There are three types of passive transport

  • Simple diffusion

  • Facilitated diffusion

  • Osmosis

Simple

• Substances move directly through the phospholipid bilayer

• HIGH → LOW

• primarily small, non polar or lipid soluble substances

• Examples

  • O2

  • CO2

  • fat-soluble molecules

Faciliated

• HIGH → LOW (down the gradient)

• Substances cross the membrane using channel or carrier proteins

  • Channels transport smaller molecules, ions

  • Carriers transport substances such as glucose and amino acids

    • charged hydrophilic → they can’t just walk through the membrane

Osmosis

• Diffusion of water across a selectively permeable membrane

Carrier- Mediated Facilitated Diffusion

• uses transmembrane carrier proteins

• Often transports larger polar molecules, such as glucose and amino acids

  • Substrate binds to carrier → carrier changes shape → substate is related on the other side

• Molecules move DOWN their concentration gradient → ni cellular energy required

  • Passive

• Transport rate is limited by the number of available carrier

  • Carrier become saturated when all binding sites are occupied

• Key distinction:

  • Channels → substances pass through a pore

  • Carrier → substances bind to the protein, which changes shape to transport them

Passive Processes: Osmosis

Goes to the place with a higher solute concentration

• net diffusion of water across a selectively permeable membrane

  • Membrane is permeable to water, but mostly impermeable to solutes

• Water moves from an area of low solute concentration → higher solute concentration

  • Equivalently: from higher water concentration → lower water concentration

• Occurs when there is a difference in solute concentration across the membrane

• Passive process

Horseshoe test tube (osmosis)

Osmolality

• Only number of solutes matter not size

• Osmolality = total concentration of dissolved particles

  • Measured in mOsm/kg of water

  • Body fluids are about 285– 295 mOsm/kg

  • Preferred over osmolarity because it is based on mass, not volume

Tonicity

effect of a solution on cell volume

• depends mainly on the concentration of non penetrating solutes

Tonicity of Solutions (isotonic)

• Isotonic

  • No net water movement

  • Cell maintain normal volume

  • Example: 0.9 % NaCl

Hypertonic

Water moves out of the cell

• Cell shrinks (crenation)

• Example: 3% NaCl

Hypotonic

Water moves into the cell

• Cell swells and may rupture'

• RBC rupture = hemolysis

  • Example: 0.45% NaCl

Effects of Tonicity on Cell Volume

• Osmosis causes cells to swell and shrink

• Change in cells volume disrupts cell function, especially in Red Blood Cells and neurons

• Aquaporins

Primary active transport

• Moves substances against their concentration gradient

  • From low → high concentration

• Requires energy

  • ATP directly provides the energy

• Uses membrane pumps (carrier proteins)

• Example

  • Na+/K+ pump

  • Pumps 3 Na + out of the cell and 2 K+ into the cell

Secondary Active transport

• Moves a substances against its concentration gradient

• Requires energy, but does not use ATP directly

  • Uses energy stored in the concentration gradient of another substance

  • One substance moves down its gradient

    • Prodives energy to move another substance against its gradient

    • The Na+ gradient is maintained by the Na+/K+ pump, which uses ATP

• Uses cotransporter carrier proteins

  • Example: Na+ —Glucose Symporter

    • Na+ moves down its gradient into the cell

    • Glucose moves against its gradient into the cell at the same time

Endocytosis

• Brings materials into the cell using vesicles

  • used to take in nutrients, fluids, or large particles

  • Phagocytosis

    • Cell eating

    • Takes in large particles such as bacteria or debris

  • Pinocytosis

    • Cell drinking

    • Takes in extracellular fluid and dissolved substances

Exocytosis

• Moves material out of the cell using vesicles

• Used to release substances such as hormones, enzymes, and neurotransmitters

• Can also remove cellular waste products

Resting Membrane Potential

• Voltage difference across the plasma membrane of a resting cell

• Inside of the cell is negative relative to the outside

• Na+ is high outside e, while K+ is high inside

• At rest, the membrane is more permeable to K+, so K+ leaks out through leak channels

• The Na+/K+ pump maintains these ion gradients by moving 3 Na+ out and 2 K+ in

• Typical neuron rating membrane potential

  • -70 mV

Nucleus

• Organelle that serves as the control center of the cell

• Contains most of the cell’s genetic material (DNA)

  • directs many cellular activities bye controlling gene expression

• Most cells contain one nucleus

• Some cells are multinucleate

  • Example- skeletal muscle fibers

• Some cells are anucleate and lack a nucleus

  • Example- mature red blood cells (RBCs)

Mitochondria

• Double membrane organelles with inner membrane folds called cristae

• Produce mosts of the cells ATP through aerobic cellular respiration

  • Requires oxygen

  • Uses energy from nutrients such as carbohydrates and fats

• Contain their own DNA and ribosomes

Cytoskeleton

• Network of protein fibers that provides structural support and helps maintain cell shape

Mircofilaments

• Thin fibers composed mainly of actin

  • Cell contraction and movement

  • Support microvilli

Intermediate filaments

• Provide mechanical strength and help stabilize cell structures

• Help cells resist stretching and pulling

Microtubles

• Hollow tubes that help organize and move structures within the cell

  • Acts as “tracks” for movement of organelles and vesicles

  • Important for cell division

  • Form the structural core of cilia and flagella

Microvilli

Small finger like extensions of plasma membrane

increase surface area for absorption

• small intestine

Core of actin filaments for stiffening

Cilia

Cell surface projections supported by mircotubules and covered by plasma membrane

Primary cilia

• Usually a single, nonmotile projection

• Acts as a sensory structure that detects signals in a cells enviorment

Motile cilia

• Less common

• Beat in coordinated waves to move material across the cell surface

• Respiratory tract

  • move mucus and trapped particles out of the air ways

• Female reproductive tract

  • help move the oocyte through the uterine tube

• Male reproductive tract

  • help move fluid and serum through parts of the reproductive tract

• Brain ventricles

  • help circulate cerebrospinal fluid (CSF)

Flagella

• also made off mircotubles

• Whip-like extension of the plasma membrane

  • longer and beat run a wave-like fusion

  • Allow the cell to move

• Only one human cell-type has this

  • SPERM

Ribosomes

• Build proteins by lining amino acids together

• Produce the primary structure of a protein

• Only starts making the protein , the protein is not functioning yet

Rough ER

• Studded with ribosomes

• Synthesizes, folds, and modifies proteins

• Especially important or proteins that will be secreted or inserted into cell membranes

Smooth ER

• Synthesizes lipid, including steroid hormones

• Helps detoxify drugs and other chemicals

• Stores Calcium (Ca2+) in certain cells , especially muscle cells , bone

Golgi apparatus

• Modifies , sorts, and packages proteins and lipis

• Packages them into vesicles for delivery to their correct destinations

• Acts like the cells “Post office”

Lysosomes

• Contains digestive enzymes

• breaks down

  • damaged organelles

  • Cellular debris

  • material borough in other the cell

• helps recycle cellular components

Peroxisomes

• Break down very long-chain fatty acids

• oxidation reactions produce hydrogen peroxide (H2O2)

• Contains catalase, which converts H2O2 into

  • Water and oxygen

• helps protect the cell from oxidative damage

  • Damaging DNA

Apoptosis

• programmed cell death that removes unneeded or damaged cells

  • Activates enzymes called caspases

    • These break down DNA and other cell components

    • Cells shrink and fragments → remnants are removed by phagocytosis (eating away at the cell)

Cell Division in Adults

Replaces short-lived cells and helps repair damaged tissues

Examples -

• blood cells

• epidermal cells

• intestinal lining

• hair follicles

Changes in Cell and Tissue Size

• Hyperplasia

• Hypertrophy

• Atrophy

Hyperplasia

increase in the number of cells

• Examples: endometrial growth during the menstrual cycle

Hypertrophy

increase in cell, tissue, muscle size

• Example: skeletal muscle growth with exercise

Atrophy

decrease in the size of a tissue or organ

• Usually involves decreased cell size and sometimes loss of cells

• Example: muscle atrophy from disease or being bed-ridden

Neoplasm

abnormal, uncontrolled cell proliferation

• May be benign or malignant

Cell Differentiation - intro

Most nucleated body cells contain essentially the same DNA, but they are not identical

• Different cell types activate different genes

  • This causes cells to produce different proteins and develop specialized structures and functions

Cell Differentiation

• Process by which cells develop specialized characteristics and functions

Stem cells

relatively undifferentiated cells that can divide and develop into specialized cell types