This document involves the key information required to understand how cells work in our bodies, the cell signalling and the significance of proteins, fats and carbohydrates. It focuses a great deal on intracellular signalling.
Cell Biology & Signalling
Lesson 1
All living organisms are made of cells. Individual cells perform specialised functions within
“communities”.
A cell is semi-independent living unit within the body, it consists of an aqueous solution of
organic molecules surrounded by a membrane.
An organelle is a subunit within a cell, with a defined structure and performing specific,
integrated activities. Some are bound by organelles, or some aren’t, e.g ribosomes.
Tissue is a group of cells, organs is a group of tissues and a system is a group of organs, all
working together respectively.
Prokaryote is where it is a single-celled organism and chromosomes is a circular strand lying
free and has no membranous organelles. Eukaryotes are cytoplasmic, membrane-bound
organelles, DNA is divided into series of linear chromosomes and considerable differences
occur.
,Only electron microscope imaging can reveal the subcellular details. TEM (transmission
electron microscope) to look inside a cell. SEM (scanning electron microscope) is to see the
cell surface (electrons scattered off cell surface by heavy metal coating). Both involve a lot of
preparation and only works on dead cells.
As cell increases in size, the volume increases more than the surface area. Diffusion at
distant less than 50micro metres, is efficient.
Specialised cells overcome the problem. Directed transport of substances around cell via
cytoskeleton. Gene expression can occur in more than one place, such as skeletal muscle
cells. Gap junctions’ channels between cells allow movements of substances between cells.
Cellular organelles are frequently bound by membranes, which allows specialised
environments to exist within them. Different functions can function in different conditions
and single cell can have different functional compartments.
Cytoskeleton is made of actin, microtubules and intermediate filaments. Actin is the muscle
and the thinnest. Microtubules is the thickest and pulls daughter cells apart. Intermediate
filaments provide mechanical strength of the cell.
Cytosol is the aqueous environment within the plasma membrane. Cytoplasm is cytosol and
the organelles.
Nucleus – Largest organelle in the cell (3-10micrometres). Contains genetic material. DNA is
organised as chromosomes. Chromatin is a complex of DNA/histone and non-histone
proteins. DNA winds around histones into nucleosomes. Nucleolus is where rDNA is
transcribed, and ribosome subunits assembled. Nuclear envelope is surrounded by two
layers of membrane. Nuclear pores allow transport in and out.
, Golgi – 4-8 closely-stacked, membrane bound channels (cisterna). It modifies proteins
delivered from RER. It modified N-linked carbohydrates and glycosylation of O-linked
carbohydrates and lipids. They create lysosomes. They direct new proteins in vesicles to
their correct compartments.
Peroxisomes – Large (0.5-1.5micrometres). It is involved in phospholipid synthesis. There is
also oxidation of very long fatty acid chains. Enzymes which generate and degrade hydrogen
peroxide. Absence of this causes disease Zellweger syndrome.
Lysosome – Membrane bound. It contains over 50 hydrolytic enzymes. All require low pH. It
is mostly involved in organelle replacement/turnover.
Mitochondria – Two layers of membrane, 0.5-2 micrometres long. Contains DNA. Sugars
oxidised, and ATP produced. Inner membrane in folds – cristae, increases surface area.
Lecture 2
Fatty acids are monomers of triaglycerols and phospholipids, the function is for long term
fat storage and structural component of membranes.
Carbohydrates, it is water soluble. General formula is (CH2O)n. The function is energy
source, in form of glucose, or energy storage in the form of glycogen. It can form the cell
wall, in bacteria. Cell surface proteins are often glycosylated and it is an important aspect
of the structure. Aldose and ketose are isomers. Aldose contain aldehyde groups whereas
ketose contain ketone groups. Humans use D-sugars.
In solution, the alpha and beta forms of glucose are in equilibrium forms.
Glycogen is a branched glucose polymer whereas amylose is linear glucose polymer.
Salivary amylase random hydrolysis of internal 1,4 linkages. Maltase then produces glucose,
which can be used by the cells.
Glycogen phosphorylase hydrolyses 1,4 linkages in glucose to produce glucose-1-phosphate.
RNA is in 3 classes, mRNA, rRNA and tRNA. mRNA is a copy of the gene and template for
protein synthesis. rRNA is the structural component of the ribosomes. tRNA is the transport
molecule for amino acids. RNA is smaller than DNA and also single stranded.
Triaglycerols (lipids) are water insoluble (hydrophobic). Triaglycerols are ester of 3 fatty
acids and glycerol. It is used in energy storage and stored in adipose tissue.
Phospholipids are amphipathic, where there is a polar head group and non-polar fatty acid
tail.
Steroids have a common multi-ring structure. Cholesterol is from diet and de novo
synthesis. Cholesterol plays a part in membrane fluidity. The precursor for steroid hormones
is testosterone, oestrogen and cortisol.
Amino acids can also act as neurotransmitters and help in the synthesis of
neurotransmitters.
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