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Summary cell biology
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Summary Cell biologyAll living things (or organisms) are built from cells: small, membrane-enclosed units filled
with the extraordinary ability to create copies of themselves by growing and dividing in two.
Every animal or plant is a vast colony of individual cells, each of which performs a specialized
function that is integrated by intricate systems of cell-to-cell communication. Cells,
therefore, are the fundamental units of life. Thus, is it to cell biology- the study of cells and
their structure, function, and behavior- that we look for an answer to the question of what
life is and how it works.
Characteristics of a cell (Robert Hooke, 1665)
- The cell has a limiting membrane (inside/ outside compartments)
- The cell contains biomolecules (e.g., proteins/ DNA/ RNA)
- A cell is an autonomous unit in performing a function (self-sustaining)
- The cell can respond &adapt to stimuli
- The cell can (often) reproduce itself
Cells can vary in size, shape, and chemical requirements. These differences are often
reflected in different cell functions. Some modifications specialize a cell so much that the cell
ceases to proliferate, thus producing no descendants. In a multicellular organism, there is a
division of labor among cells.
Only living cells can perform self-replication. Viruses also contain information in the form of
DNA or RNA, but they do not have the ability to reproduce by their own efforts. Instead, they
parasitize the reproductive machinery of the cells that they invade to make copies of
themselves. Thus, viruses are not truly considered living.
Cell theory: all living cells are formed by the growth and division of existing cells. Cells do not
arise spontaneously.
- All cells are organized
- Bacteria are the most
abundant form
- Archaea can live
under extensive
circumstances like in
volcanoes.
,The first microscope with only one lens is invented by Antonie van Leeuwenhoek.
The light microscope (works with photons, staining):
Lens types:
Eye
Occular:
Objective:
Condenser:
The advanced light microscope, fluorescence microscopy (works with photons, staining):
The electron microscope (works with electrons, staining and fixing):
- The EM has the same compartments as the light microscope
e.g., condenser lens, objective lens, projector lens.
- Light source -> electron gun
- Electromagnetics to steer the electrons
- The fluorescence screen accepts electrons and emits green
fluorescence that can be seen by the human eyes.
- Electrons are absorbed by atoms that are positive
- All organisms need to be fixed, they need to be in a vacuum,
the cell can’t live for long
- In the EM you can only look at small pieces.
,The main organelles found in Eukaryotic cells
The nucleus is the information store of the cell
The nucleus is usually the most prominent organelle in a eukaryotic cell. It is enclosed within
two concentric membranes that form the nuclear envelope, and it contains molecules of
DNA. DNA also carries the genetic information in prokaryotic cells; these cells lack a distinct
nucleus, they do not keep their DNA inside a nuclear envelope, segregated from the rest of
the cell contents. The dark spots are DNA that is used a lot. It is dark because that is where a
lot of RNA and other protein molecules are involved in the protein transcription process that
is regulating RNA production. The lighter parts are also chromatin but are not intensively
used, which is now more stored. These genes are not so active. The nuclear envelope
protects the genetic material inside the nucleus. It contains pores.
Active, thus nucleolus Not that Active, thus lighter parts Only present in cell division
Endoplasmic reticulum (ER) where RNA is translated into a protein
The endoplasmic reticulum is an irregular maze of interconnected spaces enclosed by a
membrane. It is the site where most cell-membrane components, as well as materials
destined for export from the cell, or lumen of organelles, are made. It looks like a fishnet of
connecting tubes and sheets which means a lot of membrane surface.
, Golgi apparatus; protein modification and protein sorting
The Golgi apparatus modifies and packages molecules made in the ER that are destined to
be either secreted from the cell or transported to another cell compartment. Lysosomes are
small, irregularly shaped organelles in which intracellular digestion occurs, releasing
nutrients from ingested food particles into the cytosol and breaking down unwanted
molecules for either recycling within the cell or excretion from the cell. Peroxisomes are
small, membrane-enclosed vesicles that provide a sequestered environment for a variety of
reactions in which hydrogen peroxide is used to inactivate toxic molecules. Membranes also
form many types of small transport vesicles that ferry materials between one membrane-
enclosed organelle to another.
Proteins come in
Proteins mature
Fully glycosylated, phosphorylated,
and 3D folded proteins (mature)
The mitochondria: energy supply
The mitochondria have this wavelike membrane structure to
increase the surface. They need this large surface because they
need a lot of trans-membrane to host five complexes for the
electron transport chain to make ATP. The input for mitochondria
is glycolysis that is going to a Kreb-cycle to produce ATP.
Mitochondria contain their own DNA and reproduce by dividing.
They are thought to derive from bacteria that were engulfed by
some ancestor of
eukaryotic cells.
This evidently
created a symbiotic
relationship.
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