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Chapter 4: Evolutionary Origin of Cells and Their General Features -…
Chapter 4: Evolutionary Origin of Cells and Their General Features
origin of living cells on earth
four stages:
nucleotides and amino acids produced prior to the existence of cells
nucleotides polymerized to form RNA and/or DNA, & amino acids polymerized to form proteins
polymers became enclosed in membranes
polymers that are enclosed in membranes acquire properties associated with living cells via chemical selection
prebiotic soup = medium formed by slow accumulation of organic molecules in the early oceans over a long period of time before life existed
Microscopy
three important parameters
magnification = the ratio between the size of the image and the actual size of the object
contrast = relative difference in lightness or darkness between adjacent regions in a sample
resolution = measure of the clarity of an image, the ability to differentiate between two adjacent objects
types of microscopes
light microscope = utilizes light for illumination
electron microscope = uses electron beam for illumination
TEM = a beam of electrons transmitted through biological sample to form an image on a photographic plate or screen
SEM = a beam of electrons producing the image of the three-dimensional surface of a biological sample
overview of cell structure and function
prokaryotic cells
cells that lack a membrane-enclosed nucleus and cell compartmentalization
eukaryotic cells
compartmentalized by internal membranes to create organelles
the cytosol
where synthesis and breakdown of molecules takes place
metabolism is the sum of all bodily activities and chemical reactions that occur in an organism to maintain life
catabolism = metabolic pathway for the breakdown of large molecules into smaller molecules, reactions often exergonic
anabolism = metabolic pathway that results in the synthesis of cellular molecules and macromolecules
requires an input of energy, often endergonic
enzymes = proteins that catalyze steps in the metabolic pathway, speeding up the reaction
cytoskeleton provides cell shape, organization and movement
network of three different types of protein filament
microtubules
hollow protein filament
composed of tubulin proteins
important for cell shape, organization and movement
dynamic instability = oscillation of a single microtubule between growing and shortening phases, important in sorting of chromosomes during cell division
centrosome = MTOC of non-dividing cells, located near the nucleus
intermediate filaments
protein filament
maintains shape and rigidity of animal cells
actin filaments (microfilaments)
thin protein filament
composed of actin proteins
supports the plasma membrane, key role in cell shape, strength and moment
motor proteins
type of cellular proteins that use energy (ATP) to promote movement
head, hinge, tail structure
cilia and flagella allow cells to move
cilia = cell appendages that have the same internal structure as flagella and function the same way, but are shorter and more numerous
flagella = long cell appendages that facilitate cellular movement or the movement of extracellular cells
the nucleus and endomembrane system
endomembrane system = network of membranes that includes the nuclear envelope, ER, Golgi, lysosomes, vacuoles, peroxisomes, and plasma membrane
nucleus
contains chromosomes which store most of the cells genetic material
enclosed by a nuclear envelope
nuclear pores = formed where the inner and outer nuclear membranes are in contact
the ER initiates the sorting of some proteins & carries out metabolic functions
ER = network of membranes that form flattened, fluid-filled cisternae
RER = studded with ribosomes
SER = lacks ribosomes, other metabolic functions
metabolism
storage of Ca2+ ions
lipid synthesis and modification
membrane transport = the movement of ions or molecules across a biological membrane
cell signalling = vital function of the membrane in which cells sense changes in their environment and communicate with each other
cell adhesion
vital function of cell membrane that allows cells to bind to each other
critical in the formation of multicellular organisms
provides a way to convey positional information between neighboring cells
semi-autonomous organelles = contain their own genetic material and divide by binary fission
mitochondria = supply cells with most of their ATP
endosymbiosis theory = theory that mitochondria and chloroplasts originated from bacteria that took up residence within primordial eukaryotic cells
chloroplasts = carry out photosynthesis
protein sorting to organelles
sorting signal = short amino acid sequence that directs the protein to its correct location in a cell
cotranslational sorting = the type of sorting that begins in the cytosol and then halts temporarily until the ribosome has become bound to the ER membrane
post-translational sorting = the uptake of proteins into the nucleus, mitochondria, chloroplasts, or peroxisomes that occurs after the protein is fully synthesized