Biology Ch. 6
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Light Miscroscope (LM)
- Studying Cells
- Visible light pass through specimen & then through glass lens.
- Lens refract (bend) light in such a way, it is magnified as it is projected into the eye, onto
- photographic film or a digital sensor, or onto a video screen.
- Magnify about a 1,000 times the actual size of a specimen.
Two Important parameters in microscopy are:
Magnification and Resolving Power, or Resolution
ratio of object's image size to real size
- Measure of the clarity of an image
- Defined as: minimum distance 2 points can be separated and still distinguished as two points.
Fun Fact: Most subcellular structures including organelles, which
are membrane-enclosed compartments are simply too small to be resolved by the light microscope.
So THEN: Electron Miscroscope (EM)
- Instead of light, it focuses a beam of electrons through the specimen or onto its surface.
- Electron beams have shorter wavelengths than visible light AND resolution is inversely related to the wavelength of the radiation of the microscope.
refers to the cellular anatomy that is revealed by an electron microscope.
Scanning Electron Microscope (SEM)
- Shows a 3-D image of the specimen (ex. cilia)
- Useful for detailed study of specimen.
- WORKS BY: Electron beams scans surface, which is usually coated with a thin film of gold, beam excites electrons on the surface and these secondary electrons are are detected and translated into electronic signal.
Transmission Electron Microscope (TEM)
- Used to study the internal ultrastructure of cells.
- Stained with atoms of heavy metals, which attach to certain cellular structures, thus
- enhancing density of electrons in certain regions. So electrons passing through
- specimen are concentrated in the denser regions, which only few are transmitted
Electron Microscopes vs. Light Microscopes
- EM: Pros: reveal organelles and other
- subcellular structures that are impossible with LM.
- Cons: methods used can kill cells. HOWEVER, preparation can
- introduce artifcats, structural features seen in micrographs that do not exist
- in the living cells.
- LM: Pros: study living cells
Study of cell structure (but doesn’t reveal function)
- Study of molecules and chemical processes (metabolism) of cells
- Modern cell biology mix cytology and biochemistry
- Useful technique to study cell structure and function
- BY: taking cells apart and separating the major oraganelles and other subcellular structures
- Enables researchers to prep specific cell components in bulk and identify their functions (too difficult to do if cell was intact).
- Ex. centrifugation showed an enzyme in cellular respiration and electron microscopy showed them in organelles called mitochondria. Concluded mitochondria are sites for cellular respiration. Biochemistry and cytology complement each other.
2 types of basic structural and functional units of cells are? Examples?
- prokaryotic or eukaryotic
- Pro: Bacteria and Archae
- Euk: Protists, fungi, animals, and plants
What basic features do all cells have in common?
- 1. Plasma Membrane: selective barrier that bounds the cell
- 2. Cytosol: semifluid, enclosed by membrane, that is jelly-like, where organelles and other components are found.
- 3. Chromosomes: carry genes in form of DNA
- 4. Ribosomes: complexes that make proteins according to instruction from the genes.
A major difference between prokaryotic and eukaryotic cells?
Location of their DNA, as reflected in their names.
Eukaryotic Cell (eu, true, and karyon, kernel, here referring to the nucleus)
most of the DNA is in an organelle called the nucleus, which is bounded by a double membrane.
Prokaryotic cell (pro, before, and karyon, kernel)
DNA is concentrated in a region that is not membrane-enclosed, called the nucleoid. Interior is called cytoplasm, as in eukaryotic cells (between plasma membrane and nucleus)
Prokaryotic Cells vs. Eukaryotic Cells
- Eukaryotic: within cytoplasm, suspended in the cytosol, are a variety of organelles, Thus: presence of nucleus is 1 example of a difference.
- Prokaryotic: membrane bounded organelles are absent.
- Eukaryotic cells are generally larger than prokaryotic cells.
- Functions as a selective barrier, which allows sufficient passage for: oxygen, nutrients, & waste to service the entire cell.
- For each square micrometer, only a limited amount of a particular substance can cross per second, so the ratio of surface area to volume is critical. Hence, high ratio of surface area to volume is especially important in cells that exchange a lot of material with their surroundings (ex. intestinal cells). Such cells have have many long, thing projections from their surface called microvilli, which increase surface area without an appreciable increase in volume.
Eukaryotic Cells Compartments
- Have internal membranes that divide cells into compartments, and these compartments provide diff. local environments that facilitate specific metabolic function, where it is not possible elsewhere, to have functions executed simultaneously.
- Plasma and organelle membranes also participate directly in a cell's metabolism, because enzymes are built right into the membranes.
Membranes (fundamental in cell's organization). What is it generally made up of?
- Consist of a double layer of phospholipids and other lipids, where proteins are attached or embedded as well.
- ALSO: each membrane has unique composition of lipids and proteins such as enzymes embedded in membranes of the organelles, mitochondria, involved in cellular respiration.
What is in animal cells and not plant cells?
Lysosomes, centrosomes with centrioles, and flagella (in some plant sperm)
2 cellular components involved in the genetic control of cell: nucleus, houses most of the cell's DNA and ribosomes, which uses info from the DNA to make protein.
The Nucleus: Information Central
nucleus, nuclear envelope, nuclear lamina, chromosomes, chromatin, & nucleolus.
Nucleus (in eukaryotic cells)
Contains most of the genes (some genes are located in mitochondria & chloroplasts)
Nuclear Envelope (nucleus)
- Encloses the nucleus, separating its content from the cytoplasm.
- Double Membrane, each is a lipid bilayer with associated proteins.
- Envelopes has pore structures, protein structures (pore complex) lines each pore and regulates entry and exit of most proteins & RNA's, as well as large complex macromolecules.
Nuclear Lamina (nucleus)
protein filaments (on nuclear side, not at pores) that maintain shape of the nucleus by mechanically supporting the nuclear envelope.
Chromosomes (in nucleus, DNA is organized into discrete units)
structures that carry genetic info.
Chromatin (in nucleus, make up each chromosome)
a complex of proteins and DNA
Nucleolus (in nucleus)(rRNA - assemble ribosomes)
- granules and fibers adjoining chromatin.
- rRNA (ribosomal RNA) synthesized from instructions from DNA.
- Also imported proteins from cytoplasm are assembled with rRNA into small and large ribosomal units which exit the nucleus through nucleus pores to the cytoplasm where subunits are assembled to ribosomes.
Nucleus directs protein synthesis by synthesizing messenger RNA (mRNA - synthesize polypeptides) according to instructions provided by the DNA.
mRNA is then transported to the cytoplasm via nuclear pores. Once mRNA molecules reaches cytoplasm, ribosomes (assembled by rRNA) translate the mRNA's genetic message into the primary structure of a specific polypeptide (transcribe and translate genetic info).
Ribosomes (complexes made of ribosomal RNA and protein)
- cellular components that carry out protein synthesis.
- Cells w/ high rates of protein have large numbers of ribosomes.
- Ex. human pancreas cell have a few million ribosomes.
Ribosomes build proteins in two cytoplasmic locales.
cytosol and endoplasmic reticulum/nuclear envelope
free ribosomes vs. bound ribosomes
- free ribosomes - suspended in cytosol
- bound ribosomes - attached to outside of endoplasmic reticulum (er) or nuclear envelope.
- Bound and Free - structurally identical
- function with the cytosol
- Ex. enzymes that catalyze the first steps of sugar breakdown
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