Chapter 3: Section A: Cell Structure Flashcards
Cells
cells are the structural and functional units of life
Unicellular organisms
composed of a single cell (i.e. bacteria and paramecia)
Multicellular organisms
- composed of more than one cell (i.e. humans, dogs, mushrooms, trees)
- cells are the lowest living level of organisms
Prokaryotic cells
- bacteria, archaea
- no nucleus, no membrane-bound organelles
Eukaryotic cells
- plants, animals, fungi
- have membrane-bound nucleus and membrane-bound organelles
- all have same basic structure but cells can be specialized to perform particular functions
Organelles
structures within the cell that serve a specific function (i.e. mitochondria, lysosomes)
cell size
- cells must be very small in order to function
- -> most animal cells are 10-100 micrometers
- cells must be smaller in size because the smaller the cell, the greater the surface area to volume ratio, which determines how much nutrients can enter and waste to exit
Functions of the plasma membrane
1) Regulate passage of substances into and out of cells and between bell organelles and cytosol
2) Detect chemical messengers arriving at cell surface
3) Link adjacent cells together by membrane junctions
4) Anchor cells to extracellular matrix
Fluid-Mosaic Model
- phospholipid bilayer interspersed with protein and cholesterol molecules
- consistency of olive oil –> flexible
- proteins drift sideways throughout the bilayer
- nonpolar tails of phospholipids face each other
- polar heads face outwards
Integral proteins
- bound to hydrophobic interior of phospholipid bilayer (may or may not extend from one side to other)
Transmembrane proteins
- can be used as channels or carriers
- extend all way through membrane
Peripheral
- bound to the interior or exterior surface of the membrane, usually to integral proteins.
- not ampipathic
Glycocalyx
- some membrane proteins and lipids have carbo chains attached to the cytoplasmic surface (i.e. glycoproteins and glycolipids)
- carbs from glycocalyx provides cell identity and enable cells to interact with each other
Cholesterol
- only in animal cell membranes
- reduces membrane permeability
- keeps membrane at optimal level of fluidity
- is involved in vesicle formation
Integrins
- transmembrance proteins that bind to specific proteins in the extracellular matrix and then link those proteins to other proteins in adjacent cells
specialized types of membrane junctions
- tight junctions (diffusion barrier)
- desmosomes (mechanical stability)
- gap junctions (allow direct comm. between adjacent cells)
Structure of Tight Junctions
- discontinuous series of localized fusions of adjacent plasma membranes
- forms a band around the circumference of the cell
- no extracellular space between cells (prevents leaks)
Function of tight junctions
- join most epithelial cells
- form a barrier to the extracellular space
- selective passage of substances across the epithelial layer of tissues
Function of desmosomes
- provides a strong, spot-like adhesion between adjacent epithelial cells
- mechanical stability and ability to resist separations
Structure of desmosomes
- has dense plaques and cadherins
Desmosome dense plaques
attachment plaques on cytoplasmic side of plasma membranes anchor intermediate filaments
Desmosome cadherins
- transmembrane adhesion molecules that extend into the extracellular space from dense plaque
- cadherins from adjacent cells bind to each other in a zipper-like fashion
function of gap junctions
- allows direct comm. between cells resulting in coordinated cellular activity –> homeostasis
- ions, regulatory molecules, small metabolites pass between cells through these junctions
- facilitate passage of electrical current between adjacent cells (reduce resistance)
structure of gap junction
- formed by channels/pores created by the direct alignment of 2 connexons, one in each adjacent cell membrane
- each connexon is composed of 6 connexins (integral membrane proteins)
- conformation of connexins can change, opening and closing the channels
4 components of a nucleus
- nuclear envelope, nucleolus, chromatin, nucleoplasm
Nuclear envelope
- double membrane
- contains nuclear pores that allow substances to pass
Nucleolus
- site of rRNA synthesis, initial ribosomal assembly
- contains rRNA and proteins
Chromatin
- DNA and proteins
- condenses into chromosomes in the cell cycle
Nucleoplasm
- fluid portion of nucleus
Ribosomes
- site of protein synthesis
- made of rRNA (ribosomal rna) and protein
- can be free in cytoplasm (singly or as polyribosome) or attached to rough ER
Rough ER
- network of membrane- enclosed channels/flattened sacs called cisternae
- has protein processing (i.e. carbo side-chains may be added)
- has protein folding
- has quality control: defective proteins are detected and ejected
Smooth ER
- network of membranous channels but NO associated ribosomes
- synthesis of lipids (i.e. fats are synthesized in smooth ER of liver and fat cells; steroid hormones are synthesized in smooth ER of ovaries and testes)
- detoxification of harmful substances (i.e. alcohol)
Golgi Apparatus
- network of membranous saccules (golgi bodies or cisternae)
- process proteins: phosphate or carbo groups might be added to proteins, carbo groups may be removed from proteins
- distribute proteins: proteins are sorted and shipped within transport vesicles to other parts of the cell or the plasma membrane (i.e. exocytosis/leave cell)
Transport vesicles
- piece of a membrane surrounding the substance to be transported pinches off from the organelle, travels to another organelle or the plasma membrane, and fuses with it, releasing the substance it was carrying
- RER –> Golgi and secretory vesicles
Endosomes membrane
- enclosed compartments that lie between plasma membrane and golgi app
early endosomes
- located in peripheral regions of cytoplasm
- sort and recycle proteins that enter the cell through endocytosis (i.e. recycle receptors necessary for receptor-mediated endocytosis, transport remaining proteins to late endosomoes)
late endosomes
- located near the golgi app and nucleus
- transfer substances to lysosomes and some develop into lysosomes
Mitochondria
- powerhouse of cell
- convert energy in food (glucose) into a form of energy that cells can use (ATP) via cellular respiration
Lysosomes
- membrane-bound organelles containing acids and digestive enzymes
- digest foreign particles, abnormal proteins, etc
- digest worn out cellular organelles
Peroxisomes
- membrane-bound vesicles that contain enzymes that remove O2 from substances such as lipids, alcohol, and toxins
- all reactions –> H2O2
- prevalent in lipid-metabolizing cells and involved in breaking down fatty acids into 2-carbon fragments
Cytoskeleton
- network of protein filaments that function in supporting cell structure, shape, movement, and transport
- contain actin and intermediate filaments and microtubules
Actin filaments
- microfilaments
- smallest and composed of actin
- maintain and change cell shape
- generate cell movement
- produce pseudopods to capture prey
Intermediate filamens
- intermediate in diameter
- stabilize the positions of organelles
Microtubules
- largest
- composed of tubulin
- maintains cell shape
- intracellular movement for transport via monorails and to move chromosomes via spindle fibers
Centrioles
- in animal cells and protists, centrosome contains 2 centrioles at right angles
- involved in microtubule assembly, and formation of mitotic spindle
- form basal bodies that anchor and organize cilia and flagella
- 9+0 microtubule triplet arrangement (9sets of triplets in circle)
Cilia and flagella
- found on external surface of cells
- allow cells to move
- 9+2 microtubule doublet arrangement (9 microtubules doublets around outside, 2 microtubules in center of circle)
Vaults
- cytoplasmic structures composed of protein and vault RNA (vRNA)
- associated with nuclear pores
- hypothesized function - involved in the transport of molecules between the cytosol and nucleus
- drug resistance
