apk2100c chapter 2 - cells: the living units

All living organisms are …

cellular in nature

Cells

smallest living units in our bodies

How many types of cells does human body have?

200 types

Basic survival functions cells perform

• Obtain and use nutrients

• dispose of wastes

• replicate/regenerate/repair

What carries out the basic cellular functions

Organelles

Main structural components of cell

Plasma/cell membrane, cytoplasm, and nucleus (control center)

What model used to show plasma membrane structure?

The fluid mosaic model

• dynamic structure

• mosaic = multiple components

What are the three membrane lipids in a cell?

• phospholipids

• cholesterol

• glycolipids

Fatty acid heads vs tails

• heads = hydrophilic (outside membrane)

• tails = hydrophobic (inside membrane)

Phospholipid

• amphipathic membrane lipids

  • hydrophobic and hydrophillic

• dynamic and can move around (switch spots, turn to other side)

How are membrane phospholipid arranged?

dynamic arrangement

What do phospholipids do?

create framework for plasma membrane

What percentage of membrane lipids do phospholipids take up?

Makes up 75% of membrane lipids

Cholesterol

• membrane lipid

• found among lipid tails of bilayer

• 4 ring structure

What type of organisms are cholesterol found in?

Only animal cells

What does cholesterol do for the membrane?

Structural integrity/rigidity

• Regulate fluidity

• prevent extreme changes across varying temperatures

Glycolipids (where are they found)

• membrane lipid

• only found in layer facing extracellular fluid (ECF)

• attached to phospholipid head

• carbohydrate chain

What do glycolipids do for the cell?

• Cellular adhesion and recognition

• Sticky carb chains allow adhesion

Glycoprotein

• added to protein in membrane

• carbohydrate chain

• cellular adhesion and recognition

Two general types of membrane proteins

integral and peripheral proteins

Integral proteins

• embedded in bilayer

• usually transmembrane, extending across both layers

• can be partially embedded or go completely through

Peripheral proteins

• do not extend across membrane

• loosely associated with membrane and easily separated from it

Functions of plasma membrane

1. protective barrier

2. cellular communications (via receptor proteins)

3. regulates movements of substances in and out (membrane transport)

Transport in membrane

• selectively permeable

• some solutes simply diffuse - no proteins or ATP needed

Integral proteins - transport

• transporters and channels

• assist with impermeant molecules

• carriers (passive) and pumps (active)

Simple diffusion

• Fat-soluble (lipid soluble) molecules diffuse through the phospholipid bilayer

• down a concentration gradient (high to low)

• passive

Osmosis

• water diffuses through lipid bilayer

• water requires aquaporins (channel/carrier - no ATP)

• passive

Facilitated diffusion

• particular solute moves through integral protein spanning across membrane

Active transport

• Transport proteins use ATP to actively pump substances against a concentration gradient

Endocytosis

• active transport

• cell brings in external matter by folding cell membrane to form sac/vesicle

• endosomes = vesicles

Phagocytosis

• endocytosis

• “cell eating”

• engulfing large solid particles like bacteria, cell debris, or whole cells

• large macromolecules into the cell - phagosomes

• plasma membrane forms pseudopods (extensions/hand to surround the molecule)

Pinocytosis

• endocytosis

• “cell drinking”

• small dissolved molecules in ECF

• no pseudopods

• pit is formed

• non-specific uptake of small drops of extracellular fluid and dissolved solutes

Receptor-mediated endocytosis (RME)

• endocytosis

• ligand/chemical messenger binds to receptors on the membrane to signal creation of vesicles

• Targeted uptake of specific macromolecules (ligands) that bind to membrane receptors

Exocytosis

• Active transport

• The cell moves large molecules or waste out of the cytoplasm and into the extracellular environment

• Vesicles are made of protein and fuses with membrane

• Replenish plasma membrane

Secretory vesicles

• Exocytosis

• Getting rid of waste/materials → secreting

Cytosol

• jelly-like fluid

• all other intracellular elements suspended

• water, ions, enzymes

• site of many chemical reactions

Organelles

• specialized structures

• specific functions

Membranous organelles

organelles can have single or double membrane around them

Non membranous organelles

Lack membrane

• made up of proteins or other molecules

Inclusions

• temporary structures

• pigments, protein crystals, food stores (glycogen granules and lipid droplets)

• no specific function or shape

• ex. granules that form skin color or hair color

Ribosomes

• protein synthesis

• made of proteins + ribosomal RNA (rRNA)

• small and large subunits (need both)

• non-membranous

What two locations can ribosomes be found in?

• free ribosomes in the cytosol

• ribosomes attched to rough ER

Endoplasmic reticulum (ER)

• network within the cytoplasm

• network of membrane-enclosed cavities (flattened sacs or tubules)

• membranous

Rough ER

protein synthesis

flattened sacs - cisterns or cisternae

Nucleus membrane/envelope extends to form rough ER and then SER

Smooth ER

Making or breaking down fats and calcium storage

lipid metabolism

tubular network

produce steroid hormones and aid in drug detoxification

Is RER and SER continous?

Yes, they are not separate

They transition

Golgi apparatus

• modify, sort, and package proteins and lipids for storage or transport out of cell from the ER

• vesicle from ER brings product to = CIS FACE

• product traverses through cisternae - gets modified, etc.

• TRANS FACE = shipping side

• membranous - cavity

What two vesicles does the golgi have?

• secretory vesicle = material leaving through exocytosis

• transport vesicle = material within the cell

Coordination of organelles - transport

Start at rough ER to make protein, move to cis of golgi, protein moves through cistern, leaves through trans face of golgi

Golgi apparatus - three pathways

A = vesicle destined for exocytosis

B = vesicle membrane to be incorporated into the plasma membrane

C = lysosome containing acid hydrolase enzymes (material that is not good for the cell goes here)

Lysosomes

• digest and break down

• acidic environment that works to break down materials

• breaks down proteins or part of organelles in degradations

• debris from outside of cell degradation

peroxisomes

• Smaller than a lysosome

• “Peroxide bodies”

• remove toxic waste by using special enzymes

• detoxifiers

• long fatty acid chain breakdown assistance

• smaller toxic waste or molecules (not large proteins, etc. like lysosomes do)

Peroxisomes - breakdown example

• Normal cellular metabolism produces free radicals

• free radicals (unbalanced electrons) = dangerous/destructive

• peroxisomes use oxidase to break down to hydrogen peroxide

• use catalase to break hydrogen peroxide → water

• turns material neutral using enzymes

mitochondria

• ATP production

• double membrane

  • outer and inner (more folding) mitochondrial membranes

  • space in between = intermembrane space

• cristae = folding in the inner mitochondrial membrane = increase surface area

• matrix = space in the middle

• has own DNA

mitrochondrial dna

• perfectly circular

• sensitive to damage from free radicals (produced by mitochondria during ATP production)

• only maternally inherited (all mitochondria in sperm detaches and does not become apart of embryo)

Why is there folding - cisterns and cristae?

More surface area

More packing of material like proteins

cytoskeleton

• Key structure providing framework for cell

• network of rods running through cytoplasm

• Functions like bones, muscles, and ligaments in organism

• Supports cell shape and produces movement

cytoskeleton: microfilaments

• smallest diameter

• strands made of spherical protein subunits called actins

• elongated actin strand (actin is globular)

• 7 nm

• edge of cell

microvilli (microfilaments)

Non- motile, microscopic, finger-like projections of plasma membrane

Actin on the inside

Made up of actin microfilaments - to give structure to the microvilli to stand up straight and not flop over

Increase surface area of cell for absorption

Found in absorptive cells (ex. epithelium lining small intenstines)

cytoskeleton: intermediate filaments

• medium size

• tough, insoluble protein fibers → woven rope structure

• 10 nm

cytoskeleton: microtubules

• LARGEST

• Hollow tubes of spherical protein subunits called tubulins

• 25nm

• coil form

Centrosome and centrioles

• forms microtubules

• aids in cellular division

Intermediate filaments purpose

Throughout the cell

Stabilize organelle position in cytosol and attach cells to one another

Microtubules purpose

• project outward from centrosome

• determine cells OVERALL shape

• involved in cellular movement (cilia and flagella)

  • flagella = sperm tail

  • cilia = along cell surface (small projections; brush/’stroke movement)

Nucleolus (Nucleus/N)

Site of ribosomal (rRNA) synthesis

Chromatin (N)

Genetic material of nucleus

Nuclear envelope/membrane (N)

double membrane

evaginate out to RER

Nuclear pores (N)

Little holes allowing material in and out