Cells and Cell organelles; Structure and function

Question 1

What is a cell

Answer 1

The basic, living, structural and functional unit of the body.

Question 2

What are the 3 basic parts of a cell + definitions?

Answer 2

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.

Question 3

The plasma/cell membrane is also described as a …

Answer 3

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.

Question 4

What do membrane lipids allow lipid soluble molecules to do?

Answer 4

Move across the membrane but it also prevent movement of charged or
polar ions and molecules.

Question 5

Plasma membrane structure

Answer 5

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

Question 6

What is the cell membranes fluidity/ movement? (6 points)

Answer 6

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).

Question 7

Integral proteins def + 6 examples and the most important type

Answer 7

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

Question 8

Peripheral proteins def + 2 examples

Answer 8

Are associated with one side of the membrane only Linker and enzyme proteins may be peripheral proteins.

Question 9

Important membrane proteins to remember?

Answer 9

Ion channels
Carrier proteins
Receptors
Enzymes
Linkers
Glycolipids and glycoproteins
Peripheral proteins

Question 10

Ion channels

Answer 10

Integral selective transmembrane protein (allow one type of ion only to pass) e.g. H or Cl.

Question 11

Carrier proteins

Answer 11

Selectively transports polar molecules or ions from one side of membrane to the other.

Question 12

Receptors

Answer 12

Cell recognition site; selectively binds a specific molecule e.g. insulin receptor binds to the insulin hormone.

Question 13

Enzymes

Answer 13

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.

Question 14

Linkers

Answer 14

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.

Question 15

Glycolipids and glycoproteins

Answer 15

Often cell identity markers e.g. ABO blood group determined by which glycoproteins on red blood cell membrane (A, B or A & B).

Question 16

Peripheral proteins

Answer 16

Also support plasma membrane, anchor integral proteins, do mechanical activity e.g. attach cells together.

Question 17

What is a permeable substance?

Answer 17

Substances that may pass through a structure.

Question 18

What is an impermeable substance?

Answer 18

A substance that may not pass through a structure.

Question 19

What is selectively permeable?

Answer 19

Some substances may pass through a structure more easily than others; permeability varies for each substance.

Question 20

Does the cell membrane allow permeability?

Answer 20

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.

Question 21

What is the cytoplasm+ build up?

Answer 21

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.

Question 22

What are organelles

Answer 22

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

Question 23

Structural components of the cytoskeleton?

Answer 23

Cytoskeleton : network of three filament types proteins) in cytosol; help maintain cell and organelle shape and
structure; generate movement
Microfilaments
Intermediate filaments
Microtubules

Question 24

What are the 5 membranous organelles?

Answer 24

Endoplasmic reticulum
Golgi complex
Lysomes
Mitochondria
peroxisomes

Question 25

Endoplasmic reticulum

Answer 25

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.

Question 26

Golgi complex

Answer 26

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.

Question 27

Lysomes

Answer 27

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.

Question 28

Mitochondria

Answer 28

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.

Question 29

peroxisomes

Answer 29

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)

Question 30

6 non-membranous organelles?

Answer 30

Ribosomes
Microvilli
Centrioles
Cilia
Proteasomes
Cytoskeleton
Nucleus

Question 31

Ribosomes

Answer 31

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.

Question 32

Microvilli

Answer 32

Finger like extension of the plasma membrane containing microfilaments. It increases the surface area to aid in absorption in the cell.

Question 33

Centrioles

Answer 33

Come in pairs. made from microtubules. form spindle apparatus during cell division.
Centrosome is the area of the cytoplasm surrounding centrioles.

Question 34

Cilia

Answer 34

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

Question 35

Proteasomes

Answer 35

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)

Question 36

Cytoskeleton

Answer 36

A network of fibers extending throughout the cytoplasm. it organizes cellular structures and activities, anchoring many organelles.

Question 37

Nucleus

Answer 37

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.

Question 38

Cell ageing

Answer 38

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.

Question 39

Telomeres

Answer 39

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.

Question 40

Increased autoimmunity

Answer 40

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.