Basics of Biology
The science of biology:
is the study of living things
and how they interact with their surroundings.
Cell Theory :
The cell is the basic unit of structure and function
Schleiden &Schwann (1838 – 1839)
Today the
cell theory
includes four more ideas (principals):
l - The cells are the
building block of structures
in living things
2- The cell is
derived from other cells
by division
3- The cell
contains information
for
growth
,
development
and
functioning
4- The cell is the
functioning unit of life
; the chemical reactions
of life
take place within cells.
All biological systems are similar in that they:
• Composed of the same types of chemical molecules
• Utilize similar principles in replication, metabolism, and, in
higher organisms, the ability to organize at the cell levels.
Eukaryotic and Prokaryotic cells
Prokaryotes
1- Organisms made up of cells that
lack a cell nucleus or any membrane-encased
organelles
.
2- DNA is less structured in prokaryotes than in eukaryotes. In prokaryotes,
DNA is a single loop. In Eukaryotes, DNA is organized into chromosomes.
3- Most prokaryotes are made up of just a single cell (
unicellular
)
Eukaryotes
1-
Organisms made up of cells that possess a
membrane-bound organelles
2- Genetic material in eukaryotes is contained within a
nucleus
within the
cell and DNA is organized into chromosomes.
3- Eukaryotic organisms may be
multicellular
or single-celled organisms. All
animals are eukaryotes.
Differentiation
• An important feature
of the eukaryotic cell is its ability to
differentiate
and
produce a variety of cells, each carrying out a specialized function.
• Animal cells become specialized by:
Concentrating specific organelles
and
Developing specific cellular activities
which can generally be found to more
limited extents in all animal cells.
Thus, living organisms formed from cells are highly complex and organized and
perform
a variety of functions
Function
Specialized Cell(s)
Movement
Muscle and other contractile cells
Form adhesive and tight junctions between cells
Epithelial cells
Synthesize and secrete components of the extracellular matrix
Fibroblasts, cells of bone and
cartilage
Convert physical and chemical stimuli into action potentials
Neurons and sensory cells
Synthesis and secretion of enzymes
Cells of digestive glands
Synthesis and secretion of mucous substances
Mucous-gland cells
Synthesis and secretion of steroids
Some adrenal gland, testis, and
ovary cells
Ion transport
Cells of the kidney and salivary
gland ducts
Intracellular digestion
Macrophages and some white
blood cells
Lipid storage
Fat cells
Metabolite absorption
Cells lining the intestine
Cellular Structure
In Biological systems:
water, amino acids, carbohydrates (sugar),
fatty acids, and ions
account for
75–80 %
of the matter in cells
20-25 % macromolecules
, or
polymers
(
biopolymers
), include:
• peptides/proteins
(formed from amino acids)
• polysaccharides
(formed from sugars)
• DNA
(formed from nucleotide bases and dioxyribose sugar)
• RNA
(formed from nucleotide bases and ribose sugar)
• phospholipids
(formed from fatty acids).
The main structural components of a cell are:
•
Plasma membrane:
which defines the outer boundary of a cell, present
in all cells.
•
Cell wall:
exists in the prokaryotic & eukaryotic cells of plants but not
animals.
•
Cytoplasm:
represents everything within a cell, except the nucleus.
•
Cytosol:
which is the fluid of the cytoplasm.
•
Organelle:
a subcellular compartment in a cell where a specific cellular
function takes place.
•
Nucleus:
which contains the chromosomes (genetic information).
• Organelles
are like little organs of a cell that perform various
cellular functions, just like organs perform various tasks in a
living system.
• Organelles are
intracellular
(or
subcellular
)
structures:
specifically, nucleus, mitochondria, Golgi apparatus, endoplasmic
reticulum, cytoskeleton, lysosomes, and peroxisomes.
Growth and metabolism
• Cells grow through the functioning of cellular metabolism.
• Cell metabolism
is the process by which individual cells process nutrient molecules.
• Metabolism has two distinct divisions:
1. Catabolism
, in which the cell breaks down complex molecules to produce energy and
reducing power.
2. Anabolism
, in which the cell uses energy and reducing power to construct complex
molecules and perform other biological functions.
•
Complex sugars can be broken down into simpler sugar molecules called
monosaccharides such as glucose. inside the cell, glucose is broken down to make
adenosine triphosphate (ATP).
Protein synthesis
• Cells are capable of synthesizing new proteins, which are essential for the modulation
and maintenance of cellular activities.
• This process involves the formation of new protein molecules from amino acid building
blocks based on information encoded in DNA/RNA.
• Protein synthesis generally consists of two major steps:
transcription
and
translation
.
1. Transcription
in which a particular segment of DNA is copied into mRNA
2. Translation
is the process in which ribosomes in the cytoplasm or ER synthesize
proteins after the process of transcription
