Chapter 5 and 6(a) - Cells: The Working Units of Life Flashcards
Light Microscope (LM)
- An optical instrument with lenses that refract (bend) visible light to magnify images of specimens
- Visible light is passed through a specimen and then through a glass lens
- Can magnify effectively to about 1,000 times the size of the actual specimen
- Various techniques enhance contrast and enable cell components to be stained or labeled
- Most subcellular structures, including organelles, are too small to be resolved by an LM
- Recent advances in light microscopy
- Confocal microscopy and deconvolution microscopy provide sharper images of three-dimensional tissues and cells
- New techniques for labeling cells improve resolution
The three impotant parameters of microscopy are…
- Magnification: the ratio of an object’s image size to its real size
- Resolution: the measure of the clarity of the image, or the minimum distance of two distinguishable points
- Contrast: visible differences in parts of the sample
Magnification
The ratio of an object’s image size to its real size
Resolution
The measure of the clarity of the image, or the minimum distance of two distinguishable points
Contrast
Visible differences in parts of a sample.
Organelle
Any of several membrane-enclosed structures with specialized functions, suspended in the cytosol of eukaryotic cells.
Electron Microscope (EM)
- A microscope that uses magnets to focus an electron beam on or through a specimen, resulting in a practical resolution of a hundredfold greater than that of a light microscope using standard techniques.
- Two basic types of EMs are used to study subcellular structures
- Scanning electron microscopes (SEMs)
- Transmission electron microscopes (TEMs)
Transmission Electron Microscope (TEM)
- A type of electron microscope used to study the internal structure of thin sections of cells
- Focuses a beam of electrons through a specimen
Scanning Electron Microscope (SEM)
- A type of electron microscope used to study the fine details of cell surfaces
- Focuses a beam of electrons onto the surface of a specimen, providing images that look 3-D
Cell Fractionation
- The disruption of a cell and separation of its parts by centrifugation at successively higher speeds
- Enables scientists to determine the functions of organelles
Centrifuge
- An instrument used in cell fractionation which spins test tubes holding mixtures of disrupted cells at a series of increasing speeds. At each speed, the resulting force causes a fraction of the cell components to settle to the bottom of the tube, forming a pellet. At lower speeds, the pellet consists of larger components, and at higher speeds smaller components.
Cytology
- The study of cell structure
- Cytology and Biochemistry help correlate cell function with structure
Biochemistry
- The study of the chemical processes (metabolism) of cells
- Biochemistry and Cytology help correlate cell function with structure
The basic features of all eukaryotic cells and prokaryotic cells
- Plasma membrane
- Cytosol
- Chromosomes
- Ribosomes
Cytosol
The semifluid portion of the cytoplasm.
Cytoplasm
- The contents of the cell bounded by the plasma membrane
- In eukaryothes, the portion exclusive of the nucleus
Chromosome
- A cellular structure carrying genetic material
- found in the nucleus of eukaryotic cells
- Each chromosome consists of one very long DNA molecule and associated proteins
- Found in the nucleoid region in bacterial cells
- A bacterial chromosome usually consists of a singular circular DNA molecule and associated proteins
Prokaryotic cells are characterized by having…
- No nucleus
- DNA in an unbound region called the nucleoid
- No membrane-bound organelles
- Cytoplasm bound by the plasma membrane
Nucleoid
A non-membrane-bounded region in a prokaryotic cell where the DNA is concentrated
Eukaryotic cells are characterized by having…
- DNA in a nucleus that is bounded by a membranous nuclear envelope
- Membrane-bound organelles
- Cytoplasm in the region between the plasma membrane and the nucleus
Plasma Membrane
- The membrane at the boundary of every cell that acts as a selective barrier, regulating the cell’s chemical composition
- Allows sufficient passage of oxygen, nutrients, and waste to service the volume of every cell
- The general structure of a biological membrane is a double layer of phospholipids
- The boundary that separates the living cell from its surroundings
- Exhibits selective permeability, allowing some substances to cross it more easily than others
As the surface area of a cell increases by a factor of n2, the bolume increases by a factor of…
- n3
- Metabolic requirements set upper limits on the size of cells, so the surface area to volume ratio of a cell is critical
- Small cells have a greater surface area relative to volume
Parts of a eukaryotic cell present in animal cells but not in plant cells:
- Lysosomes
- Centrosomes, with centrioles
- Flagella (present in some plant sperm)
Parts of an Animal Cell
Parts of a plant cell:
Parts of a eukaryotic cell present in plant cells but not in animal cells:
- Chloroplasts
- central vacuole
- Cell wall
- Plasmodesmata
Nucleus
- Contains most of the cell’s genes and is usually the most conspicuous organelle
Ribosome
- A complex of rRNA and protein molecules that functions as a site of protein synthesis in the cytoplasm
- Particles made of ribosomal RNA and protein
- consists of a large and a small subunit
- In eukaryotic cells, each subunit is assembled in the nucleolus
- Carry out protein synthesis in two locations
- In the cytosol (free ribosomes)
- On the outside of the endoplasmic reticulum or the nuclear envelope (bound ribosomes)
Nuclear envelope
- In a eukaryotic cell, the double membrane that surrounds the nucleus, perforated with pores that regulate traffic with the cytoplasm. The outer membrane is continuous with the endoplasmic reticulum.
- The nuclear membrane (the double membrane) consists of two lipid bilayers
Nuclear Lamina
The shape of the nucleus is maintained by the nuclear lamina, which is composed of protein.
Chromatin
- The complex of DNA and proteins that makes up eukaryotic chromosomes.
- When the cell is not dividing, chromatin exists in its dispersed form, as a mass of very long, thin fibers that are not visible with a light microscope
- Chromatin condenses to form discrete chromosomes as a cell prepares to divide
Nucleolus
- A specialized structure in the nucleus consisting of chromosomal regions containing ribosomal RNA (rRNA) genes along with ribosomal proteins imported from the cytoplasm
- The site of rRNA synthesis and ribosomal subunit assembly
Components of the Endomembrane System:
- The collection of membranes inside and surrounding a eukaryotic cell, related either through direct physical contact or by the transfer of membranous vesicles
- Includes:
- Nuclear envelope
- Endoplasmic reticulum
- Golgi apparatus
- Lysosomes
- Vacuoles
- Plasma membrane
Vesicle
A membranous sac in the cytoplasm of a eukaryotic cell.
- Transport vesicle: Carries molecules produced by the cell