cell physiology Flashcards
Describe the basic structure of the plasma membrane
surrounds the cell and most intracellular organelles.
- consists of a double layer of lipid molecule with embedded proteins (called phospholipid bilayer)
What molecules make up the plasma membrane? Describe each in detail
Consists of phospholipids, cholesterol and glycolipids along with carbon and oxygen as primary molecules.
- Phospholipids are amphipathic with polar head groups and non polar tails.
- Cholesterol is a steroid that is also amphipathic and maintains cell fluidity (prevents phospholipids from touching each other)
- Glycolipids are lipids with a small CHO chain attached (also amphipathic) and form glycocalyx which is involved with identification and interaction between cells
What is the function of the plasma membrane? (4 things)
- Physical barrier (keeps organelles and proteins inside the cell, maintains fluid composition and homeostasis/ pH balance)
- Cell-to-Cell communication (contains receptors that bind to specific signalling molecules arriving at cell surface)
- Structural support (contains cell junctions and connections between plasma membranes or between membranes and ECF materials)
- Transport (selectively permeable)
What is the function of the organelle membrane?
they reflect different functions of cells or organelles and have different content of lipids and proteins
What are the functions of desmosomes? What is its structure?
desmosomes are adhering junctions that anchor cells together in tissues that are subject to considerable stretching (like heart muscles)
- they are made up of the following proteins:
1 . plaques —> anchoring point for cadherins
2. Cadherins–> link cells together
3. Intermediate filaments –> structural supper and to anchors cytoskeleton of one cell to another to share the stress of stretching
What are the functions of tight junctions? What is its structure?
Tight junctions are found in epithelial tissue
- involved in molecular transport
- consist of:
1. occluding (link adjacent cells together to form impermeable function and limits movement of molecules between cells so molecules pass THROUGH cells instead) - essential for polarized cells
What is the function of gap junctions? What is its structure?
gap junctions are transmembrane channels linking cytoplasms of adjacent cells
- allows small molecules and ions to move between cells
- are made up of connexions
What is the basic function and structure of the nucleus?
basic function of the nucleus is transmission of genetic material and contains information for protein synthesis Has: - nuclear envelope (porous) - nuclear pores - nucleolus (where RNA synthesis occurs) and Chromatin (DNA associated w proteins)
what is basic function and structure of endoplasmic reticulum?
The rough ER:
- synthesis of proteins with bound functional ribosomes
- water soluble proteins, transmembrane proteins and post-translational modification of proteins
- Granular, with ribosomes on its surface
- flat
The smooth ER:
- synthesizes lipids, stores Calcium and involved in drug detoxification in liver cells
- argranular, with no ribosomes
- tubular
What is the basic function and structure of Golgi apparatus?
Composed of cisternae which have many vesicles.
- sorts and packages proteins
it preforms post translational modification on them and then packages them up in vesicles and sends them to their destination
What is the basic function and structure of lysosomes and peroxisomes?
lysosomes are digestive enzymes that are hydrolytic (break down large molecules to their smaller subunits)
- function at pH 5.0
- recycle organelles and destroy endocytose bacteria and viruses
Peroxisomes
- use oxygen to remove hydrogen from molecules
- a lot in kidney and liver
- breaks down a toxic called = 2H2O2 —> 2H2O + O2
What is the basic function and structure of mitochondria?
is the cell’s powerhouse, and consists of a double membrane and is involved in cellular respiration (production of ATP from oxygen)
What are two non membranous structures?
Ribosomes and cytoskeleton
What is the function and structure of ribosomes?
Ribosomes are non-membrane bound and they are involved in protein synthesis
they have two subunits called small and large and stye are composed of RNA
The two major types of functional ribosomes are free ribosomes and ribosomes bound to rough ER
What is the function and structure of cytoskeleton?
non-membrane bounce and is made up of protein filaments that sit in the cytoplasm.
- they maintain cell shape, maintain organelle positions and mediate cell and organelle motility (flagella)
What compromises the cytosol?
- Water, high potassium concentration, and low sodium concentration.
- High protein concentration. Carbohydrates, amino acids and lipids.
- Inclusion bodies (storage granules for triglycerides)
- Secretory vesicles (move to surface of cell when hormone needs to be released).
What are the different forms of vesicular transport? Define endocytosis and the three types of endocytosis? Define exocytosis?
Endocytosis --> uptake of material into a cell via vesicles that pinch off from cell membrane The three types of endocytosis are: 1. Phagocytosis "cell eating" 2. Pinocytosis "cell drinking" 3. Receptor-mediated endocytosis
Exocytosis is the release of material from the cell via vesicles that fuse with the cell membrane
What are the three driving forces of non-vesicular transport?
- Chemical
- Electrical
- Electrochemical
Describe chemical driving forces
when molecules flow passively down their concentration gradients (from high to low concentration). As size of gradient increases, the rate of transport of substance increases.
Describe electrical driving forces
when the cell’s membrane potential (difference in electrical potential or voltage across cell membrane) causes flow of certain ions into or out of the cell.
Describe electrochemical forces
the sum of electrical and chemical driving forces acting on ion. Direction depends on net direction of electrical and chemical driving forces
Define simple diffusion
Passive movement of molecules through a biological membrane’s lipid bilayer. it does not require energy
What factors determine if a substance can cross a membrane by simple diffusion?
- solubility in lipid (polar or non polar)
- Size (smaller diffuse more readily)
- High to low concentration
What factors influence the rate of simple diffusion? Describe each
- Magnitude of driving force
- Membrane surface area (higher the Sa, the higher rate of SD)
- Membrane permeability –>
- non polar cross easily
- smaller and more regularly shaped diffuse faster
- increasing temperature increases diffusion rate
- rate of diffusion inversely proportional to the distance (thicker membrane is longer time to diffuse)
Which factor is most important in determining if a substance can cross a membrane by simple diffusion?
Lipid solubility of diffusing substances
What are the two types of facilitated transport and what do they have in common?
The two types are carriers and channels. They are both passive transport (does not require energy)
What is the difference between the movement of molecules across plasma membranes via carrier and via a channel?
carrier mediated facilitated diffusion is when the protein in the membrane undergoes a conformational change to allow binding of a molecule and is continuously working until concentrations on each side of membrane are equal
- does not require energy
Channel mediated facilitated diffusion
- selective and involves electrochemical gradient that determines the ion flux coming in or out
- can be voltage gated, ligand gated, or mechanically gated (stretch or swell to open)
- channels need something to open it
What is the difference between primary and secondary active transport? provide an example of each
Primary active transport DIRECTLY hydrolyses ATP ( ATP –> ADP + pi)
- an example is the sodium potassium pump
What is the difference between saturable and non saturable transport?
Secondary active channels use electrochemical gradients from another ion channel that is moving an ion down its electrochemical gradient.
involves cotransport, counter transport (symport and anti port)
Define single transduction?
sequence of events between the binding of the molecule to the receptor and the production of a cellular response
Define the role of first and second messengers
- First messengers is an extracellular chemical messenger that binds to a specific membrane receptor
- Second messengers are substances that enter or are generated in the cytoplasm of a cell in response to the binding of an extracellular messenger
What is the difference between lipid-solvable and lipid-insolvable chemical messengers? Where are the receptors located to which they bind?
Lipid soluble messengers can diffuse through the plasma membrane while lipid-insoluble (water-soluble) messengers need protein (receptors) to cross membrane.
- lipid soluble chemical messengers bind to receptors in cytosol or nucleus (straight to the point)
- lipid insoluble chemical messengers bind to receptors on extracellular surface of plasma membrane (channel-linked receptors, enzyme linked receptors and g-protein linked receptors)
How do lipid-soluble chemical messengers produce an effect in the cell?
alter the transcription of mRNA by binding to response element and they alter the rate of synthesis of a particular protein (either increases or decreases mRNA responsible for a particular protein)
What are two mechanisms of intercellular communication (between cells)?
Direct –> gap junctions
and
Indirect –> chemical messengers (incl. lipid-soluble or lipid-insoluble (water soluble)
What are 3 properties of receptors?
- Specificity –> binds to specific ligand
- Saturation –> can be saturated if all the binding sites are filled with ligands
- Affinity –> binds with high strength of interaction to the ligand
Describe the role of channel-linked receptors?
- proteins that function as a receptor and ion channel
1. First messengers bind to receptor that opens the ion channel
2. ions cross membrane
3. change in electrical properties of the cell - -> these are fast and can include calcium channels for muscle contractions
Describe role of enzyme-linked receptors?
proteins that function as a receptor also have intrinsic enzyme activity
- i.e. can phosphorylate a molecule as it crosses
Describe role of G-protein linked receptors?
- binds GDP and GTP and has 3 subunits: alpha, beta and gamma
- first messenger binds to receptor
- alpha subunit binds to guanosine nucleotides and adds a phosphate to it making it active –> GTP.
- GTP powers the effector protein somewhere else in the cell
What are G-proteins? What are the steps involved in the G-protein cascade?
G proteins:
- effect ion channels (causing them to open or close)
- Stimulate G-proteins: activate enzymes
- Inhibit g-proteins: inhibit enzymes
Describe the steps in the cAMP second messenger system
a
Describe the steps in the calcium-calmodulin second messenger system
aa
What is signal amplification?
ability of small changes in concentration of a chemical messenger to elicit marked responses in target cells
What are 3 different types of membrane proteins? Describe each. What are 2 properties of them.
- Phospholipids are amphipathic with polar head groups and non polar tails.
- Cholesterol is a steroid that is also amphipathic and maintains cell fluidity (prevents phospholipids from touching each other)
- Glycolipids are lipids with a small CHO chain attached (also amphipathic) and form glycocalyx which is involved with identification and interaction between cells
- Glycoproteins are proteins with attached carbohydrates that form glycocalyx for cell communication
- Distributed unequally and selectively permeable.
