Download CELL PHYSIOLOGY Cell: are the basic structural and functional

CELL PHYSIOLOGY
Cell: are the basic structural and functional units of the human
body & there are many different types of cells (e.g., muscle, nerve,
blood, and so on) Many of the functions of cells are performed by
particular subcellular structures known as Organelles.
COMPONENTS OF THE CELL
1- Water
comprises 60 - 90% of most living organisms (and cells)
important because it serves as an excellent solvent & enters into many
metabolic reactions
found in both intra- & extracellular fluid
2- Carbohydrates
about 3% of the dry mass of a typical cell
composed of carbon, hydrogen, & oxygen atoms (e.g., glucose is C6H12O6)
an important source of energy for cells :
3- Lipids
about 40% of the dry mass of a typical cell
composed largely of carbon & hydrogen
generally insoluble in water
4- Proteins
about 50 - 60% of the dry mass of a typical cell
subunit is the amino acid & amino acids are linked by peptide bonds
2 functional categories = structural (proteins part of the structure of a cell like
those in the cell membrane) & enzymes
5- Nucleic Acids
DNA
RNA (including mRNA, tRNA, & rRNA)
Cell organelles:
1) Cell membrane:
Consist of tow primary building blocks include lipid and proteins
Functions of cell membrane
1- keep the shape of the cell
2- include all of the cell organelles
3- allow permeability of ions in & outside the cell
4- Has carriers, pores & channels to transport ions
2) Cytoplasm:
Cytoplasm consists of a gelatinous solution and contains microtubules (which
serve as a cell's cytoskeleton) and organelles.
Cells also contain a nucleus within which is found DNA (deoxyribonucleic
acid) in the form of chromosomes plus nucleoli (within which ribosome's are
formed)
3) Organelles in the cell:
Golgi complex consists of a series of flattened sacs (or cisternae)
functions include: synthesis (of substances likes
phospholipids), packaging of materials for transport (in
vesicles), and production of lysosomes
Endoplasmic reticulum comes in 2 forms: smooth and rough; the surface of rough ER
is coated with ribosomes; the surface of smooth ER is not

functions include: mechanical support, synthesis (proteins by
rough ER & lipids by smooth ER), and transport
Lysosomes membrane-enclosed spheres that contain powerful digestive
enzymes
functions include destruction of damaged cells (which is why
they are sometimes called 'suicide bags') & digestion of
phagocytosed materials (such as bacteria)
Ribosome'scomposed of rRNA (ribosomal RNA) & protein
may be dispersed randomly throughout the cytoplasm or
attached to surface of rough endoplasmic reticulum
often linked together in chains called polyribosomes or
polysomes
primary function is to produce proteins
Mitochondria (power house) have a double-membrane: outer membrane & highly
convoluted inner membrane
inner membrane has folds or shelf-like structures called
cristae that contain elementary particles; these particles
contain enzymes important in ATP production
primary function is production of adenosine triphosphate
(ATP)
Centrioles paired cylindrical structures located near the nucleas
play an important role in cell division
Flagella & cilia Hair-like projections from some human cells
cilia are relatively short & numerous (e.g., those lining
trachea)
a flagellum is relatively long and there's typically just
one(e.g., sperm)
Nucleus and Nucleolus The nucleus is the brain of eukaryotic cells. It is only present in eukaryotic
cells (which are eukaryotic because they have a nucleus) and there is only one of
these organelles in each cell. Usually the nucleus is round and is the largest organelle
in the cell.
What makes up a nucleus?
A thin nuclear membrane
The nucleolus
The chromatin
Lipid material in the nucleus-nucleoplasm
DNA & Synthesis of protein
The nucleus houses the DNA
(deoxyribonucleic acid) which stores genetic
information for a cell. The DNA contains
instructions for the production of the cell's
proteins and for reproduction. To construct
proteins, the DNA is copied to messenger
RNA (ribonucleic acid) in the process called
transcription. The mRNA goes to the
ribosome's, either in the nucleus or in the
endoplasmic reticulum, where the actual
construction of the proteins takes place.
Function of nucleus:
Have genes for genetic information
Control chemical reactions inside the cell
Control reproduction and division of the cell
TRANSPORT across CELL Membranes
1 - Passive processes Require no expenditure of energy by a cell:
simple diffusion = net movement of a substance from an area of high
concentration to an area of low concentration. The rate of diffusion is
influenced by:
o
concentration gradient
o
cross-sectional area through which diffusion occurs
o
temperature
o
molecular weight of a substance
o
distance through which diffusion occurs
.
Facilitated diffusion = movement of a substance across a cell membrane from
an area of high concentration to an area of low concentration. This process
requires the use of 'carriers' (membrane proteins). In the example below, a
legend molecule (e.g., acetylcholine) binds to the membrane protein. This
causes a conformational change or, in other words, an 'opening' in the protein
through which a substance (e.g., sodium ions) can pass.
Osmosis = diffusion of water across a semipermeable membrane (like a cell
membrane) from an area of low solute concentration to an area of high solute
concentration for example: the red blood cell in hypertonic medium will
shrunk & in hypotonic medium will rupture.
2 - Active processes:
Movement of a substance across a cell membrane from an area of low
concentration to an area of high concentration using a carrier molecule in presence of
energy
Primary active transport:
Needs carrier (protein)
Needs energy
Occurs uphill (from low concentration to high concentration of solute)
Can be inhabited by some drugs such as qiunidines
For example: sodium potassium pump
Secondary active transport:
Needs carrier which has two sites one for sodium binding & the other for
glucose, amino acid or galactose binding.
Occur at the brush boarder of the intestinal & renal cells.