Cells and Cell organelles; Structure and function Flashcards
What is a cell
The basic, living, structural and functional unit of the body.
What are the 3 basic parts of a cell + definitions?
Plasma/cell membrane: Flexible structure separating internal contents from the external environment; selective barrier; allows communication with external environment.
Cytoplasm: Cytosol (fluid) containing water with dissolved molecules and organelles e.g. mitochondria, ribosomes.
Nucleus : large organelle containing genes in chromosomes; controls protein production for cell structure and function.
The plasma/cell membrane is also described as a …
Fluid mosaic model : membrane is a constantly moving sea of lipids with a mosaic of proteins. Some proteins move whilst others are anchored.
Proteins embedded in the bilayer allow movement of ions. Proteins can be receptors to bind other molecules e.g. hormones. Others (MHC proteins) signal to immune cells that they are normal, healthy body cells.
What do membrane lipids allow lipid soluble molecules to do?
Move across the membrane but it also prevent movement of charged or
polar ions and molecules.
Plasma membrane structure
Basic construction is a lipid bilayer: mostly phospholipids (75%), cholesterol (20%) and glycolipids (5%).
Phospholipid bilayer: two phospholipid layers with fatty acid
tails in the center
Phosphate “head”: polar; hydrophilic; faces cytosol and
extracellular fluid (ECF)
Lipid “tails”: non polar; hydrophobic; face towards each
other in the interior
What is the cell membranes fluidity/ movement? (6 points)
Cell membrane is not rigid.
•Lipids and many proteins can rotate and move sideways in their half of the bilayer.
•Flexibility depends on two things: number of double bonds in fatty acid tails and cholesterol.
•More double bonds = more flexible
•Cholesterol strengthens lipid bilayer but membrane less flexible at body temperature; at low temperature cholesterol increases membrane fluidity.
•Important : allows self sealing if membrane penetrated; allows movement during cell division and secretion of substances (plus other roles).
Integral proteins def + 6 examples and the most important type
Firmly embedded extend into or across lipid bilayer.
Most integral proteins are transmembrane proteins which protrude
into cytosol and ECF.
Integral proteins function as: ion channels, carrier proteins,
receptors, enzymes, linker proteins or cell identification
markers
Peripheral proteins def + 2 examples
Are associated with one side of the membrane only Linker and enzyme proteins may be peripheral proteins.
Important membrane proteins to remember?
Ion channels Carrier proteins Receptors Enzymes Linkers Glycolipids and glycoproteins Peripheral proteins
Ion channels
Integral selective transmembrane protein (allow one type of ion only to pass) e.g. H or Cl.
Carrier proteins
Selectively transports polar molecules or ions from one side of membrane to the other.
Receptors
Cell recognition site; selectively binds a specific molecule e.g. insulin receptor binds to the insulin hormone.
Enzymes
Catalyze specific reactions at either the inside or outside of the cells surface. for example lactase protruding from epithelial cells lining the small intestine splits the disaccharide lactose in the milk you drink.
Linkers
They anchor membrane proteins to neighboring cells or protein filaments providing structural stability and shape for the cell. May also partake in the movement of the cell or linkage between 2 cells.
Glycolipids and glycoproteins
Often cell identity markers e.g. ABO blood group determined by which glycoproteins on red blood cell membrane (A, B or A & B).
Peripheral proteins
Also support plasma membrane, anchor integral proteins, do mechanical activity e.g. attach cells together.
What is a permeable substance?
Substances that may pass through a structure.
What is an impermeable substance?
A substance that may not pass through a structure.
What is selectively permeable?
Some substances may pass through a structure more easily than others; permeability varies for each substance.
Does the cell membrane allow permeability?
Yes. Cell membrane highly permeable to non polar (lipid soluble) molecules e.g. O 2 , CO 2 and steroid hormones.
Small polar molecules with no overall charge e.g. water (also via aquaporins) and urea move across membrane when gaps appear due to lipids moving.
Transmembrane proteins: channel and carrier proteins move charged molecules e.g. ions.
What is the cytoplasm+ build up?
Cytosol + organelles
Cytosol : fluid part of cytoplasm; 75-90% water plus dissolved and suspended substances e.g. amino acids, glucose, ions, fatty acids, proteins, lipids, ATP.
Site of many biochemical reactions e.g. glycolysis.
What are organelles
Tiny individual structures/components within the cytoplasm that each have
a different function.
Cells contain a wide range of organelles: some structural; some membranous and some without membranes.
Membrane bound compartments allow specialized functions to be performed within them
Structural components of the cytoskeleton?
Cytoskeleton : network of three filament types proteins) in cytosol; help maintain cell and organelle shape and structure; generate movement Microfilaments Intermediate filaments Microtubules
What are the 5 membranous organelles?
Endoplasmic reticulum Golgi complex Lysomes Mitochondria peroxisomes
Endoplasmic reticulum
Flat, folded, membranous sacs attached to nuclear membrane.
Two types: rough and smooth
Rough ER (RER): continuous with nuclear membrane; has ribosomes attached; synthesizes membrane proteins, secretory proteins and organelle proteins.
Smooth ER (SER): extends from RER; synthesizes fatty acids and steroid hormones; detoxifies lipid soluble drugs and releases glucose into the blood.
Sarcoplasmic reticulum = SER in muscle cells; stores calcium ions (Ca 2+2+) needed for muscle contraction.
Golgi complex
Consists of stacks that modify, store and route products of the ER. Synthesizes some macromolecules, notably non-cellulose poly saccharides. It releases product into vesicles.
Lysomes
A vesicle containing digestive and hydrolytic enzymes able to digest foods and recycle all waste into proteins/ food particles. Have an internal PH of 5 (slightly acidic). Release breakdown products into cytosol e.g. amino acids, glucose, fatty acids. Digest worn out cell structures and damaged /dying cells Sperm lysosomal enzymes digest their acrosome (protective cap) for fertilisation to occur.
Mitochondria
Surrounded by 2 phospholipid bilayer with the outer membrane being more permeable than inner as it is folded into shelves in order to increase surface area so more proteins and enzymes can attach to it.
Its role is cellular respiration such as extraction of energy from sugars, fats and other fuels.
peroxisomes
Specialized metabolic compartments bound by a single membrane. It contains enzymes that remove hydrogen from various molecules and transfers them to oxygen producing hydrogen peroxide (H2O2)
6 non-membranous organelles?
Ribosomes Microvilli Centrioles Cilia Proteasomes Cytoskeleton Nucleus
Ribosomes
A small structure made of 2 subunits of ribosomal RNA and proteins. Carries out protein in the cytosol (ICF) and on the outside of the ER (binds to RER).
Site of protein production.
Microvilli
Finger like extension of the plasma membrane containing microfilaments. It increases the surface area to aid in absorption in the cell.
Centrioles
Come in pairs. made from microtubules. form spindle apparatus during cell division.
Centrosome is the area of the cytoplasm surrounding centrioles.
Cilia
An extension of the plasm membrane containing microtubules that can move that is longer then microvilli. it can either move something along the surface of the cell or used to move the cell (sperm cell) it is then called a flagella .Can also act as a sensor of the ecf
Proteasomes
Tiny stack of four protein rings around a central core containing proteases (protein digesting enzymes).
Destroy unneeded or faulty proteins plus proteins in biochemical pathways after they have performed their function
Break proteins into peptides; other enzymes break peptides into amino acids (recycled into new proteins)
Cytoskeleton
A network of fibers extending throughout the cytoplasm. it organizes cellular structures and activities, anchoring many organelles.
Nucleus
Largest organelle surrounded by a nuclear double membrane (each consisting of double lipid bi layer) with pores to regulate entry and exit of materials.
Most cells have one nucleus; red blood cells have none; skeletal muscle cells have multiple.
Commands and controls the center of the cell.
Controls cell structure, directs cell activities, produces ribosomes in nucleoli (singular: nucleolus).
Contains DNA in 23 pairs of chromosomes.
Cell ageing
As cell structure and function change, homeostatic responses decline leading to the body being more vulnerable to disease, infection, environmental stressors.
Some body cell types never divide e.g. skeletal and cardiac muscle cells, most neurons have or have limited capacity to undertake mitosis
Outcome of both: damaged cells may not be replaced to reduction in function of tissue/organ
Ageing genes (normal genes important for cell function) reduce in activity as we age slows down vital cell processes.
Telomeres
Are protective DNA “cap” on chromosome ends; typically get shorter each cell division. Telomerase enzyme adds the protective DNA cap/telomere. High stress level will lead to shorter telomere length.
Increased autoimmunity
As membrane protein changes increase, cell identity markers may be affected
Altered cell identity markers e.g. MHC proteins may lead to antibodies which bind to the membrane causing cell destruction.
As protein changes increase, autoimmune response increases leading to loss of tissue and reduction in function.
