Please enable JavaScript.
Coggle requires JavaScript to display documents.
Tour of Cells & Membrane Structure (CHAPTER 6 (PROKARYOTE VS.…
Tour of Cells & Membrane Structure
CHAPTER 6
MICROSCOPY
microscopes invented in 1590 and refined in 1600s
cell walls first seen by Robert Hooke in 1665 looking at dead tree cells through a microscope
microscopes first used by renaissance scientists
TYPES OF MICROSCOPES
LIGHT MICROSCOPE (LM)
visible light is passed through the specimen and then a glass lenses
lenses bend light in a way were the image of the specimen enlarges
ELECTRON MICROSCOPE (EM)
focuses a beam of electrons through the specimen or onto its surface
resolution is related to wave length of the light or electrons
SCANNING ELECTRON MICROSCOPE (SEM)
very useful for detailed studies of topography of a specimen
electron beam scans the surface of the sample, usually coated in a thin film of gold
beam exited electrons on the surface, and these secondary electrons are detected by a device that translates the pattern of electrons into an electronic signal sent to a video screen
TRANSMISSION ELECTRON MICROSCOPE (TEM)
is used to study the internal structure of cells
aims an electron beam through a very thin section of the specimen, much as a light microscope aims light through a sample on a slide
electrons passing through the specimen are scattered more in the denser regions, so fewer are transmitted
image displays the pattern of transmitted electrons
CELL FRACTIONATION
useful technique for studying cell structure and function
takes cells apart and separates major organelles and other subcellular structures from one another
piece of equipment needed is called centrifuge, spins test tube holding mixtures of disrupted cells at a series of increasing speeds
enables researchers to prepare specific cell components in bulk and identify their functions, a task not usually possible with intact cells
SURFACE AREA VS.VOLUME RATIO
for each square micrometer of membrane, only a limited amount of a particu- lar substance can cross per second, so the ratio of surface area to volume is critical
As a cell (or any other object) increases in size, its surface area grows proportionately less than its volume
Area is proportional to a linear dimension squared, whereas volume is proportional to the linear dimension cubed
surface area is the area of all sides of something added together
volume is the amount of space that a substance or object can hold
PROKARYOTE VS. EUKARYOTE STRUCTURE
Bacteria and Archaea consist of prokaryotic cells
Protists, fungi, animals, and plants consist of eukaryotic cells
All cells are bounded by a selective barrier, the plasma membrane also called the cell membrane
All cells have a cytosol
All cells have chromosomes, which carry genes in the form of DNA
All cells have ribosomes
The major difference is the location where DNA is located
Eukaryotic Cell: inside the nucleus
Prokaryotic Cell: DNA is in a region that's not membrane closed, inside nuclei
CHAPTER 7
MEMBRANE PROTEIN FUNCTIONS
TYPES OF MEMBRANE PROTEINS
PERIPHERAL PROTEINS
not embedded in the lipid bilayer at all
loosely bound to the surface of the membrane, often to exposed parts of integral proteins
INTEGRAL PROTEINS
hydrophobic regions of an integral protein consist of one or more stretches of non- polar amino acids typically 20–30 amino acids in length, usually coiled into α helices
penetrate the hydrophobic interior of the lipid bilayer
majority are transmembrane proteins, which span the membrane; other integral proteins extend only partway into the hydrophobic interior
hydrophilic parts of the molecule are exposed to the aqueous solutions on either side of the membrane
Some proteins also have one or more hydrophilic channels that allow passage through the membrane of hydrophilic substances
TRANSPORT
protein that spans the membrane may provide a hydrophilic channel across the membrane that is selective for a particular solute
Other transport proteins shuttle a substance from one side to the other by changing shape
Some of these proteins hydrolyze ATP as an energy source to actively pump substances across the membrane.
ENZYMATIC ACTIVITY
protein built into the membrane may be an enzyme with its active site exposed to substances in the adjacent solution
some cases, several enzymes in a membrane are organized as a team that carries out sequential steps of a metabolic pathway
SIGNAL TRANSDUCTION
membrane protein may have a binding site with a specific shape that fits the shape of a chemical messenger, such as a hormone
The external messenger may cause the protein to change shape, allowing it to relay the message to the inside of the cell, usually by binding to a cytoplasmic protein
CELL- CELL RECOGNITION
Some glyco- proteins serve as identification tags that are specifically recognized by membrane proteins of other cells
This type of cell-cell binding is usually short-lived
INTERCELLULAR JOINING
Membrane proteins of adjacent cells may hook together in various kinds of junctions, such as gap junctions or tight junctions
This type of binding is more long-lasting
ATTACHMENT TO THE CYTOSKELETON AND EXTRACELLULAR MATRIX (ECM)
Microfilaments or other elements of the cytoskeleton may be noncovalently bound to membrane proteins, a function that helps maintain cell shape and stabilizes the location of certain membrane proteins
Proteins that can bind to ECM molecules can coordinate extracellular and intracellular changes
TYPES OF ACTIVE TRANSPORT
Sodium-Potassium pump, Exocytosis, and Endocytosis.
SODIUM- POTASSIUM PUMP
exchanges Na+ for K+ across the plasma membrane of animal cells
powered by ATP
EXOCYTOSIS
the cell secretes certain molecules by the fusion of vesicles with the plasma membrane
transport vesicle that has budded from the Golgi apparatus moves along microtubules of the cytoskel- eton to the plasma membrane
ENDOCYTOSIS
the cell takes in molecules and particulate matter by forming new vesicles from the plasma membrane
proteins involved in the processes are different, the events of endocytosis look like the reverse of exocytosis
a small area of the plasma membrane sinks inward to form a pocket. Then, as the pocket deepens, it pinches in, forming a vesicle containing material that had been outside the cell
DIFFUSION
the movement of particles of any substance so that they spread out into the available space
Osmosis- diffusion of free water across a selectively permeable membrane, whether artificial or cellular,
Tonicity - ability of a surrounding solution to cause a cell to gain or lose water.
isotonic- a cell without a cell wall, such as an animal cell, is immersed in an environment
hypertonic- cell will lose water, shrivel, and probably die
