Week 1: Cells

What are organelles?

Specialized structures within the cell that perform specific functions in cellular growth, maitainence, and reproduction.

Identified by their specific/characteristic shape

Nucleus

Site of genetic material - DNA

Site of transcription of DNA to RNA

Contains Nucleoli - regions of ribosome assembly

Surrounded by double membrane containing nuclear pores - nuclear envelope

Chromatin - DNA packed around histone proteins. Some regions are transcribed into RNA

Nucleolus

Found in the nucleus - regions of ribosome assembly

Nuclear Envelope

Double membrane separating the nucleus from the cytoplasm.

Both layers of membrane are are lipid bilayers similar to plasma membrane - containing nuclear pores 

Outer membrane of NE is continuous with RER - protein synthesis

Rough Endoplasmic Reticulum (RER)

Network of membranes in the form of flattened sacs or tubules that occupies much but not all of the cytoplasm.

Studded with ribosomes (site of protein synthesis) - large SA for efficient protein synthesis

Disease changes position of ribosome

Smooth Endoplasmic Reticulum (SER)

System of internal membranes that aids in the manufacturing of carbohydrates/lipids ( not proteins - No ribosomes)

Golgi Apparatus

“Maturation and packaging” - Assemble, modify, proteins/molecules to form glycoproteins, glycolipids, and lipoproteins, and package molecules made by the cell

Secretory vesicles

Located throughout the cell - transporting material from Golgi to cell surface via membrane fusion - excreting materials

*cytoskeleton = highway network of cell to move vesicles

Mitochondrion

Site of aerobic resp - to produce ATP

Outer mitochondrial membrane - Similar in structure to plasma membrane

Inner mitochondrial membrane - similar to plasma membrane with series of folds (cristae) = huge SA for chem reactions of aerobic phase of cellular respiration (glucose catabolism) to produce ATP

Central fluid filled cavity = matrix

Peroxisome

Vesicle that are responsible for metabolism and detoxification of potentially harmful molecules

Site of oxidative reactions for various organic substances

Site of fatty acid metabolism

Lysosome

Vesicle formed from Golgi complex, containing digestive enzymes

Cytoplasm

Consists of all cellular contents between plasma membrane and nucleus

Two components - cytosol and organelles

Cytosol - fluid portion (water, dissolved solutes, suspended particles).

Cytoskeleton

“highway network and scaffolding of the cell”

Filamentous network throughout the cytoplam

3 systems - actin filaments, intermediate filaments, and microtubules

Functions: Cell division, Basis of microvilli and cilia, vesicle  transport, contractility, mechanical strength

Endocytic Network

Take up and digestion

Vesicular system taking up (coated vesicles - clathrin), transporting and sorting (endosomes) or degrading (lysosomes) macromolecules and worn out cell components

What is the fluid mosaic model?

Structural model used to describe the plasma membrane - a continually moving (fluid) sea of fluid lipids containing a mosaic of different proteins. Essentially it is:

phospholipid bilayer containing:

peripheral proteins and integral proteins,

channel protein,

cholesterol,

glycoprotein (glucose attached to protein),

glycolipid (glucose attached to lipid).

Describe the permeability of the plasma membrane, can any molecule just diffuse across?

Selectively permeable membrane - lipid soluble (lipophilic) hormones and dugs can diffuse across to get into cells,

But water soluble drugs and hormones cannot, so must bind with receptors in the plasma membrane - activating an intracellular response

Acts as a barrier between intra and extracellular environments

Are phospholipid bilayers polar or non-polar?

They are AMPHIPATHIC - they are both polar and non-polar

Hydrophilic (polar) head groups and hydrophobic (nonpolar) acyl hydrocarbon chains are covalently bonded together in the same molecule

This dictates how complex lipids behave in water (aggregate in different non covalently bound structures to satisfy the needs of differing solubility parts of lipids - energetically most favorable structure = VERY STABLE)

Arrangement of membrane proteins - Integral/ Transmembrane/ peripheral proteins

Intergral - extend into or through the lipid bilayer and a re firmly embedded into it. Most are also transmembrane proteins (span the entire lipid bilayer- extruding into the cytosol and extracellular fluid) 

Peripheral - not as firmly embedded in the membrane. Attached to the polar heads of membrane lipids or to integral proteins at the inner or outer surface of the membrane

Glycoproteins vs Glycolipids vs Glycoalyx

Proteins or lipids with carbohydrate groups attached to the ends that protude into the extracellular fluid,

Glycoalyx are when the carbohydrate sections of these glycoproteins/lipids form an extensive sugary coat.

what is the role of glycoalyx?

Forms a “signature“ that allows cells to recognise each other - because the pattern of carbohydrates in the glycoalyx varies from one cell to another

Cells can adhere to each other.

Protects cells from being digested

What are different functions of membrane proteins?

ion channel (integral),

carriers (integral) - selectively move a polar ion/substance from one side of membrane to another,

receptor (integral)- cellular recognition,

enzyme (integral and peripheral) - catalyze specific chem reactions in/out of cell,

linkers (integral and peripheral) - anchor proteins in the plasma membrane,

cell identity marker (glycoprotein) - allows cells to recognize each other from potentially harmful material

What are linker membrane proteins?

Anchors filaments inside and outside the plasma membrane = structural stability and shape for cell

May also participate in movement of cell or to link cells together

What are receptor membrane proteins?

Recognises specific ligand and alters cells function in some way

EG: ADH binds to receptors in the kidney and changes the water permeability of certain plasma membranes

What are cell identity markers proteins?

Distinguish your cells from everyone else’s ( unless identical twins)

EG: Major histocompatability (MHC) proteins

What kind of molecules can passively diffuse across plasma membranes?

Hydrophobic molecules - CO2, 02 N2

Lipid soluble - ethanol, steroid hormones

What factors affect diffusion rates across a membrane?

steepness of concentration gradient,

temperature (hotter = more KE),

mass of diffusing substance (small diffuse faster),

surface area (larger SA of membrane, faster),

diffusion distance.

what are examples of active processes that are involved in transport across membranes?

active transport and endocytosis

what are examples of passive processes that are involved in transport across membranes?

Simple diffusion, facilitated diffusion (channel proteins)

What are two forms of facilitated diffusion?

Channel mediated: solute moves down a conc grad across the lipid bilayer through a membrane channel - most of which are ion channels that are often specific to an ion, e.g K+ or Cl-

Carrier mediated:(solute binds to carrier on one side and is released on other side following a change in shape of carrier protein).

what substances are moved across the membrane by facilitated diffusion?

glucose, fructose, galactose and some vitamins

Active transport - What is it?

Active process of solutes being moved against a concentration gradient - uses energy ( two sources) to power ATPases to move ions or small molecules across the membrane against a chemical conc grad or electrical con grad

1) ATP is hydrolysed to provide energy (primary active transport)

2) Energy stored in an ionic concentration gradient (secondary active transport)