BIOL Topic 2 Flashcards
When did the first prokaryote form
3.5 bya
The first organisms were likely
prokaryotes
Domains Archaea and Bacteria form distinct branches but inherited simple prokaryotic cell organization from _____
a common ancestor
Why do prokaryotic cells differ from eukaryotic cells
Prokaryote cells are small (0.5 - 5 µm) and unicellular, diffusion limits the size in prokaryotic cells, have circular genomes (lack a nucleus), and lack membrane-bound organelles
Structural and functional adaptations that contribute to the prokaryotic success
cell surface structures, endospores, mobility, simple internal organization and DNA, and reproduction
Cell wall
maintains cell shape, protects the cell, and prevents it from bursting in a hypotonic environment (lower solute concentrations than cell contents)
Peptidoglycan
a network of sugar polymers cross-linked by polypeptides
Bacterial cell walls contain
peptidoglycan
Archea cell walls contain polysaccharides and proteins but lack _____
peptidoglycan
peptidoglycan
a network of sugar polymers cross-linked by polypeptides
Gram Stain
Can be used to classify bacteria by cell wall composition
Gram-positive bacteria
have simpler walls with large amount of external-facing peptidoglycan
Gram-negative bacteria
have less peptidoglycan and an outer lipopolysaccharide membrane
Lipopolysaccharide outer membrane
can contain toxins that _____
resist antibiotics
Capsule
a sticky polysaccharide/protein layer that surrounds prokaryotes
Capsules adhere to
cells and other surfaces
Biofilms
communities of cells in a slimy extracellular
matrix
Capsules retain ___ protecting the cells against desiccation
water
fimbriae
hair like appendages that help cells adhere to a substrate or other individuals in a colony
Pili
are longer than fimbrae and allow prokaryotes to exchange DNA
Endospores
Endospores are small, rounded, resting
cells that form inside some prokaryotes
when conditions become unfavorable
Endospores have a tough coat that is:
resistant to UV light, chemicals, heat, high salt, and extreme pH
Endospore formation is induced by
_______, such as an increase
in heat or lack of nutrients. Endospores remain dormant until environmental conditions are suitable for ____
environmental stress, growth
About ____ of known prokaryotes are motile
half
Most motile prokaryotes propel
themselves by:
flagella
Taxes
The ability to move toward or away from a
stimulus, e.g. positive phototaxis is
the movement towards light (most prokaryotes exhibit this
Prokaryotic cells usually lack:
complex compartmentalization, membrane-bound organelles (nucleus, mitochondria, chloroplast)
Example of a prokaryote that have specialized membranes that perform metabolic functions:
Thylakoid membranes in cyanobacteria
Prokaryotes have small genomes consisting of:
single circular chromosomes that are enclosed in the nucleoid region
Plasmids
small rings of DNA containing a few extra genes (some species of bacteria also have these)
Prokaryotes reproduce by
binary fission (asexual reproduction)
Binary fission process:
- DNA replicates
- Cell elongates itself
- cell splits into two (daughter cells are identical)
Factors contributing to prokaryote genetic diversity
rapid reproduction, mutations, genetic recombination
Genetic recombination
combining DNA from two sources and contributes to genetic diversity
Horizontal gene transfer
movement of genes among individuals from different species
Genetic recombination of prokaryotic DNA from different individuals can occur by
transformation, transduction, and conjugation
Transformation
uptake and incorporation of foreign DNA
from the surrounding environment
Transduction
the transfer of a portion of DNA between bacteria by bacteriophages (viruses that
infect bacteria)
Conjugation
occurs when genetic material is transferred between prokaryotic cells through direct contact (a donor cells transfers DNA to a recipient cell) which can recombine with the bacterial chromosome of the recipient cell
____ are often trasferred during conjugation
plasmids
Plasmids ofte carry _____ resistance ans is why horizontal gene transfer is one reason why antibiotic resistance spreads so quickly
antibiotic
Types of sources of energy for prokaryotes
- light (phototrophs)
2. from chemicals (chemotrophs)
Two types of sources of carbon for prokaryotes
- inorganic molecules such as CO2 (autotrophs)
2. organic substrates (heterotrophs)
Obligate aerobes
require O2 for cellular respiration
Obligate anaerobics
are poisoned by O2 and use termination or anaerobic respiration
Facultative anaerobic
can survive with or without O2
biological nitrogen fixation
some bacteria and methanogens use this process to convert atmospheric nitrogen to ammonia
Nitrogen is needed for
production of amino acids and nucleic acids, obtain N from a limited range of N-containing compound
two lineages of prokaryotes
domain bacteria and domain eukaria
______ include the vast majority of familiar prokaryotic species
bacteria
5 types of bacteria
alpha, beta, gamma, delta, and Epsilon
Proteobacteria
a large and metabolically diverse group of Gram-negative bacteria with 5 sub-lineages (alpha to epsilon)
Alpha
(proterobacteria) many are closely associated with aeukaryotic cells
hypothesized that mitochondria of eukaryotes evolved from:
aerobic alpha proteobacteria through endosymbiosis
Gamma and epsilon proteobacteria
include
pathogens
Chlamydias
parasites that live within animal cells. They lack peptidoglycan in their cell walls
Cyanobacteria
produce O2 through phototrophy
Domain Archea shares ____ with bacteria
simple prokaryotic cell organization inherited from a common ancestor
Archea thrives where:
energy availabe for growth is too limited to support bacteria or Eukariotes
Subdomain Bacteria is divided into 5 clades:
Euryarchaeotes, Thaumarchaeotes, Aigarchaeotes, Crenarchaeotes, and Korarchaeotes
Methanogens
archea that lives in anoxic habitats like marshes and swamps and produces methane as a waste product
Extreme Halophiles
live in highly saline environments
Extreme thermophiles
archea that thrives in very hot environments
Prokaryotes often form ____ relationships with larger organisms
symbiotic
