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Summary Cell Biology Lectures (AB_1138)
All my cell biology lecture notes, but in great detail. These helped me pass the course with an 7,5.
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Cell Biology LecturesCells and Organelles
Learning objectives for cells and cell organelles:
- Define what a cell is and to which groups it can belong;
- Explain different microscopy methods and choose the best microscopy method to answer a
specific research question;
- Identify the key organelles of the cell and explain their prime function.
* histology becomes cell biology when zooming in to individual cells takes place. From tissue
to cells and from cells to sub-cellular structures.
Cell biology is the study of cell structure and function, and it revolves around the concept that
the cell is the fundamental unit of life. Focusing on the cell permits a detailed understanding of
the tissues and organisms that cells compose.
Essential features of a cell:
- The essential building block of all life on Earth;
- The presence of a limiting membrane, i.e. a lipid membrane/phospholipid bilayer:
distinguishment between internal environment and external environment. This
distinguishment allows for gradients and specific biochemical interactions that only happen
within the cytosol (intracellular liquid) or that only happen outside of the cell;
- Contains biomolecules (DNA, RNA, proteins, etc.);
- An autonomous unit in performing a function;
- The ability to respond and adapt to stimuli;
- The ability to (in most cases, an example of an exemption are nerve cells) reproduce itself.
Biomolecules: molecules that are present in an organism that are essential to one or more
biological processes. These molecules are one of the basic ingredients of a cell. Biomolecules
are essential for cells to react to their outside environment. For example, the very important
biomolecules DNA, RNA and proteins perform distinct and concrete functions that are critical
for the cell function.
* the three-dimensional structure of a basic component relates to that component’s function.
Bacteria and archaea (prokaryotes) are cells without cell organelles. This does not mean that
these cells are not internally structured. For this they use protein and RNA complexes.
Bacteria No nucleus or other organelles, most abundant type of cell, divide quickly and
can adapt very quickly to their external environment.
Archaea No nucleus, thus prokaryotic, often extremophilic (the ability to survive in
extreme environments).
Eukaryotes Nucleus and other organelles, sometimes multicellular forms of life.
,In cell biology, the relation between the morphology and function of cells is studied. How does
a cell contribute to the behaviour of an organism?
Light microscopy uses light microscopes. The light microscope and its lenses (from bottom to
top): light source > condenser lens (concentrates the light of the light source onto the specimen)
> specimen > objective lens (magnification, focal plane) > eyepiece/(bin)ocular (determines the
final 10x magnification) > the human eye > retina (translates the light information into a visual
picture).
In fluorescence microscopy (advanced light microscopy), instead of using all light (white
light), only one colour/specific wavelength is used. This specific wavelength is conducted by
putting a filter (first barrier filter) between the light source and the objective lens. The objective
lens then reflects light and this light is filtered by the second barrier filter. The dichromic mirror
reflects the blue light that the studied object is sending but transmits the green light that the
object is sending. For example, the Aequorea victoria uses the blue light of the ocean to emit a
green glow.
Sometimes, fluorescence microscopy does not provide sufficient information to be able to study
the cell’s organization. This happens when the to be studied object is smaller than the
wavelength of any light; the limit of the light microscope lies around 500 nm. This is why
electron microscopy (EM) is used for such small object rather than light microscopy (LM).
The difference is that EM cannot produce colour, whereas LM can.
An electron microscope functions the exact same way as a light microscope. The electron
microscope and its electromagnetic, negatively charged, lenses (from top to bottom): electron
gun > condenser lens (forms a beam of electrons out of the electron cloud) > specimen >
objective lens (determines magnification and focus) > fluorescent screen (contains chemicals
that can transform electrons into fluorescence and ultimately a visual picture, as humans are not
able to see electrons) > eyepiece.
Advantages of EM over LM Disadvantages of EM compared to LM
- Superior resolution (up to 0.5 nm - Requires fixation of cells due to vacuum
atoms); operation;
- Visualisation of the entire cell, not only - Only small pieces of tissue can be
a fluorescent probe (e.g. GFP); imaged;
- Huge magnification range (30x – - Time-consuming method.
300.000x.
,The morphology and function of organelles
- Nucleus: big round sphere that consists of
a dense part, the nucleolus, and a less
dense part. The nucleus is surrounded by
a double membrane called the nuclear
envelope. DNA and their associated
proteins (chromatin), many RNAs and
protein molecules are found within the
nuclear envelope. The dark and dense
nucleolus is the region where a lot of
DNA processes take place. The lighter
region is a place with less active genes. DNA itself is also structured; chromatin is a complex
of DNA and protein that forms chromosomes. The genetic material and its processes need
to be heavily protected by the nuclear envelope. The nuclear envelope with a double
membrane functions as a gatekeeper for what enters and exits the nucleus (inside/outside
distinction). Functions: storage of the hereditary information of an organism, control of
protein and enzyme synthesis, control of cell division and cell growth, stores RNA and
ribosomes, regulation of the transcription of mRNA to a protein.
- Endoplasmic Reticulum: this organelle is continuous with the nuclear envelope. The
structure of the rough endoplasmic reticulum consists of tubes (two-dimensional)/fishnets
(three-dimensional) with ribosomes attached to it. Function: translation of RNA to a protein.
The endoplasmic reticulum produces proteins that are designated for the lumen of other
organelles within the cell, or proteins that are designated for the external environment
relative to the cell. The lumen of the ER and of most other organelles is completely
continuous with the lumen of the outside environment.
* not only the plasma membrane, but also the lipid membranes of the cell organelles (except
for the nucleus) protect the difference between the internal environment (cytosol) of the cell
and the external environment of the cell; the inside/outside barrier.
- Golgi Apparatus: the Golgi complex consists of a
stack of sheet-like structures. Function: maturation
and modification of proteins, posttranslational
modification of the three-dimensional structure of the
protein, sorting of matured proteins for transport to
lysosomes, the plasma membrane, secretory vesicles.
- Mitochondrion: this organelle also contains a double
membrane, of which both membranes enwrap the
contents of the organelle in a cisternae-like manner.
This causes the membrane surface area to be highly
increased. The amplification of the surface area is
done in order to obtain a lot of ATP membrane complexes. These are transmembrane
protein complexes for which you, of course, need membranes. Function: the production of
ATP via transmembrane protein complexes. The Krebs Cycle and the Electron Transport
, Chain are important systems by which glucose is dissimilated. Mitochondria contain their
own mitochondrial DNA (endosymbiosis theory), causing them to be quite independent.
- Chloroplast: the counterpart of mitochondria in cells. Function: energy supply in plants via
photosynthesis. Photosynthesis is highly driven by membranes containing chlorophyll
granules, which is why chloroplasts contain stacks of membranes. Carbon dioxide and water
react, using light energy, to produce glucose and oxygen. Plants still need mitochondria to
burn the glucose that is provided by photosynthesis: glucose and oxygen react to produce
carbon dioxide, water and energy (ATP).
- Cytoplasm: the ‘structure’ of this organelle can be described as a dynamic, active, jelly
matrix full of proteins rather than a homogeneous liquid. Functions: transport, protein
synthesis (on ribosomes in the cytosol), protein breakdown, signal transduction, membrane
fusion, ionic homeostasis, membrane fusion. One of these processes is, for example, the
formation of and transport by the cytoskeleton. The cytoskeleton is made up of filaments
(actin for actin filaments, a tubulin subunit for microtubules, intermediate filaments).
Function: the formation and containment of cell shape, intracellular transport.
* the cytoplasm consist of the cytosol, where protein synthesis and protein degradation takes
place, and of organelles, which carry out specific functions.
* the abundance of a specific organelle is related to the cell type.
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