II. General Structure of Prokaryotic and Eukaryotic Cells
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What are prokaryotes?
bacteria and archaea
What are eukaryotes?
Similarities between them.
- enclosed by membrane regulating passage of materials called hte plasma membrane
- Inside each cell is a semifluid jellylike substance called cytosol in which subcellular components are suspended
- Chromosomes (carry genes in DNA)
- Interior= cytoplasm (in euk, its the region between the nucleus and plasma membrane)
- - DNA in nucleus (bound by double membrane)
- - organelles with special shape and function are in cytosol
- - Subdivided by internal membranes into various membrane-enclosed organelles
- - Larger
- - DNA in nucleoid (non membrane-enclosed)
- - lacks organelles
Why are eukaryotic cells bigger?
- size relates to function
- Logistics of carrying out
- metabolism sets limits on cell size
- Impose theoretical __ on __ that is practical for single cell.
--- __ is a selective barrier htat allows passage of oxygen, nutrients, and waste
---------- For each __, only a little can cross per second.
- upper limits
- plasma membrane
- square micrometer
- Surface area to volume ratio
Surface area to volume Ratio
- As a cell increases in size, its volume grows proportionately more than its surface area
- A smaller object has a greater ratio of SA to volume
Larger organisms dont have larger cells, but more cells
High SA: Volume important in cells that exchange a lot
Microvilli increase SA without a large volume increase
- __ through internal membranes (__), which provide __.
- Plasma membrane and organelle membranes have __ built right into membranes.
- different environments
- double layer of phospholipids and other lipids with proteins embedded or attached
- Each membrane is unique
Explain prokaryotic reproduction.
- Involves growth to roughly double its size and division called binary fission (also relates to asexual reproduction of single-celled eukaryotes)
- - Does not involve mitosis
- - Genes carried on a single bacterial chromosome that consists of a circular DNA molecule and associated proteins
- - Process is initiated when DNA of bacterial chromosome begins to replicate at a place called the origin of replication, producing two origins
- ---- As it continues to replicate, one origin moves rapidly toward opposite end of the cell, causing cell elongation
- When it is twice its size, its complete and splits in two
Movement of Bacterial chromosomes is reminiscent of the __ movements of the __ regions of eukaryotic chromosomes during __ of mitosis, but bacteria don't have visible __ or __.
Several proteins play a role in __.
- mitotic spindles
- chromosome movement
Evolution from prokaryotic to eukaryotic
- a. Prokaryotic Species:
- i. Well adapted to extreme environments and can adapt to broad range of habitats
- 1. most abundant organisms on earth
- a. Subject to natural selection
Most are unicellular, vary in shape, and are well-organized
What does hte cell wall do?
Compare to Eukaryotes and Bacterial
- maintains cell shape, protects cell, and prevents it from bursting in a hypotonic environment
- eukaryotes: made of cellulose or chitin
- Bacterial: contain peptidoglycan, a polymer composed of modified sugar cross-linked by short polypeptides
Explain the bacterial cell wall.
Encloses entire bacterium and anchors other molecules htat extend from its surface
Cell wall is surrounded by sticky later of polysaccharide or protein called a capsule if it is dense and well-defined or a slime layer if well organized
What does hte capsule or slime layer enable?
Both kinds enable prokaryote adherence to substrate or others in colony and protect against dehydration and shield pathogenic prokaryotes from attacks by hosts’ immune system
Archael cell wall
contains variety of polysaccharides and proteins but lack peptidoglycans
Using __, prokaryotes are separated into two groups based on differences in cell wall composition.
Gram negative: __
- Gram stain
- GP: simpler walls with large amounts of peptidoglycan
- GN: less peptidoglycan are structurally more complex with outer membrane containing lipopolysaccharides
Gram staining has __ implications.
The __ portions of the __ in walls are toxic, causing fever or shock. Furthermore, the outer membrane of a __ helps protect it from the body’s defenses and are more resistant to antibiotics because outer nembrane impedes entry of drugs
- gram-negaitve bacterium
Gram staining treatment implications:
Antibiotic effectiveness from __
Resulting __ may not be functional
inhibition of peptidoglycan cross-linking
Some prokaryotes stick to their substrate or to one another through __, hairlike appendages.
What are fimbriae?
Fimbriae are shorter and more numerous than pili, appendages that pull two cells together prior to DNA transfer from one cell to another; sometimes called sex pili
½ of prokaryotes capable of __, a directed movement toward or away from a stimulus
__: change movement pattern in response to chemicals
ex: Toward __; away from __
- nutrients or oxygen
iMovement aided by __, which may be scattered over surface or concentrated at one or both ends
Differences from eukaryotic flagella
- 1/10 the width
- Not covered by extension of plasma membrane
- Differ in molecular composition and mechanism of propulsion
Among prokaryotes, bacterial and archaeal flagella are similar in __and __, but are composed of different __.
Three main parts: __
- rotation mechanism
motor, hook, filament
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