Chapter 4 Flashcards
(44 cards)
1
Q
Essential nutrients
A
-are those that must be supplied from the environment.
2
Q
Macronutrient
A
- Major elements in cell macromolecules- C, O, H, N, P, S
- Ions necessary for protein function- Mg2+, Ca2+, Fe2+, K+
3
Q
Micronutrients
A
- Trace elements necessary for enzyme function
- Co, Cu, Mn, Zn, and others
4
Q
Autotrophs
A
- fix CO2 and assemble it into organic molecules.
- Photoautotrophs
- Chemoautotrophs (or lithotrophs)
5
Q
Phototrophs
A
-obtain energy from light, transformed into chemical energy
6
Q
Heterotrophs
A
- use preformed organic molecules that originated from autotrophs.
- Photoheterotrophs
- Chemoheterotrophs (or organotrophs)
7
Q
Chemotrophs
A
- obtain energy from chemical oxidation-reduction reactions
8
Q
Lithotrophs
A
- use inorganic molecules as a source of electrons
9
Q
Organotrophs
A
- use organic molecules
10
Q
Energy Is Stored for Later Use
A
- A membrane potential is generated when chemical energy is used to pump protons outside of the cell.
- The H+ gradient plus the charge difference form an electrochemical potential, called the proton motive force (PMF).
- The potential energy stored in the PMF can be used to transport nutrients, drive flagellar rotation, and make ATP by the F1FO ATP synthase.
11
Q
The Nitrogen Cycle
A
- Nitrogen fixers possess nitrogenase, the enzyme that converts N2 to ammonium ions (NH4+).
- Nitrogenase is destroyed by oxygen
- Nitrifiers oxidize ammonia to nitrate (NO3–).
- Denitrifiers convert nitrate to N2
12
Q
Nitrogen-fixing bacteria
A
- may be free-living in soil or water, or they may form symbiotic associations with plants.
- Rhizobium bacteria are symbionts with leguminous plants such as soybeans, chickpeas, and clover
- The root nodules produce the microoxic environment required by the nitrogenase enzyme
13
Q
Selective permeability
A
- Substrate-specific carrier proteins, or permeases
- Dedicated nutrient-binding proteins in the periplasmic space
- Membrane-spanning protein channels or pores
14
Q
Facilitated diffusion
A
- helps solutes move across a membrane from a region of high concentration to one of lower concentration.
-Is selective for specific molecules
-It does not use energy and cannot move a molecule against its gradient.
Example: the aquaporin family that transports water and small polar molecules such as glycerol
15
Q
Coupled transport systems
A
- energy released by an ion moving down its gradient is used to move a solute up its gradient.
- In symport, the two molecules travel in the same direction.
- In antiport, the two molecule moves in opposite directions
16
Q
ABC transporters
A
- largest family of energy-driven transport systems is the ATP-binding cassette superfamily
- found in all three domains of life
17
Q
ABC transporters- Two main types
A
Uptake ABC transporters
- are for transporting nutrients into the cell.
- Use a periplasmic solute-binding protein
Efflux ABC transporters
-which include multidrug efflux pumps
18
Q
Group translocation
A
-a type of active transport that uses energy to chemically alter the substrate during its transport.
19
Q
phosphotransferase system (PTS)
A
- type of Group translocation
- example present in many bacteria.
- It uses energy from the metabolite phosphoenolpyruvate (PEP) to attach a phosphate to specific sugars.
- The phospho-sugar cannot leak back out of the cell, and is ready to be metabolized
20
Q
two main types of culture media used to grow bacteria
A
- Liquid, often called broth
- Useful for studying the growth rate and for obtaining cell mass for study, industry, or biotechnology - Solid (usually gelled with agar),
useful for:
-Separating species from mixed cultures from clinical specimens or natural environments
-Counting colonies, each from a single cell
Observing differential growth characteristics
21
Q
Colonies are isolated via two main techniques
A
- Streaking
- Dragging a loop across the surface of an agar plate
- Diluting the sample to obtain single isolated colonies - Spread plate
- Tenfold serial dilutions are performed in liquid culture medium
- A small amount of each dilution is then “plated”, spread on a plate of solidified medium
- Goal is to find a dilution that produces isolated colonies
22
Q
Growth Factors
A
- specific nutrients required by some organisms include certain vitamins and amino acids.
- These growth factors must be available in growth medium
- examples of some organisms that require specific growth factors include staphylococcus and mycobacterium
23
Q
pure culture
A
- Microbes in nature exist in complex, multispecies communities
- for detailed studies they must be grown separately
24
Q
Complex media
A
- are nutrient rich but poorly defined.
- might contain yeast or beef extract, protein mix, etc.
25
Synthetic media
- made from specific chemicals such as salts, glucose or other sugars, specific amino acids, etc.
- A defined minimal medium contains only the compounds needed for an organism to grow.
26
Enriched media
-complex media to which specific components such as blood are added to support growth of certain bacteria
27
Selective media
-favor the growth of some organisms over others, so the organisms of choice are not obscured by the presence of numerous other organisms.
28
Differential media
-produce visible differences between two species that grow equally well, so each type can be counted
29
Direct Counting of Living and Dead Cells
- Microorganisms can be counted directly by placing dilutions on a special microscope slide and examination with a microscope.
- But you cannot tell if a cell is living or dead
30
Fluorescence-Activated Cell Sorter (FACS)
- Stained fluorescent cells are passed through a small orifice, one cell at a time, and then past one or more lasers.
- Some detectors measure light scatter to determine the number and size of all cells.
- Other detectors measure fluorescence
31
Other Techniques for Counting
- A viable (living) bacterium can replicate and produce a colony on a solid medium.
- Viable cells can be counted via the spread plate (cells on top of the agar) or pour plate (cells mixed in the agar) methods
- Microorganisms can be counted indirectly via biochemical assays of cell mass, protein content, or metabolic rate.
- Used for biotechnology
- Measuring the optical density (OD) of a bacterial liquid culture or suspension with a spectrophomometer is often the fastest and easiest way of determining the number of bacteria.
- Direct relationship between OD and number of cells
32
binary fission
- the way most bacteria divide
- one parent cell splits into two equal daughter cells.
- some divide asymmetrically
33
Growth rate
- rate of increase in cell numbers or biomass of a bacterial culture
- Rapid bacterial growth is called “exponential” because it generates an exponential curve, a curve whose slope increases continually.
- Cell numbers double every time interval
- If a cell divides by binary fission, the number of cells in a culture is proportional to 2n, where n = number of generations
34
Generation Time
-the time it takes for a population to double
-For cells undergoing binary fission,
Nt = No x 2n
Nt= is the final cell number
No= is the original starting cell number
n= is the number of generations, which is the time of growth divided by the generation time.
35
batch culture
- simplest way to model the effects of a changing environment is to culture bacteria
- A liquid medium within a closed system
- changing conditions in this system greatly affect bacterial physiology, gene expression, and growth.
- The bacteria adapt to the changing environment by changing their gene expression and metabolism.
36
Stages of bacterial Growth
Lag phase- no growth because cell have to adjust to the new environment
Log phase- doubling every unit of time
Stationary phase- all nutrients are used and no more growth can occur
Death phase- lack of nutrients and build up of waste products causes death
37
continuous culture
- all cells in a population achieve a steady state, which allows detailed study of bacterial physiology.
- A chemostat apparatus ensures logarithmic growth by constantly adding and removing equal amounts of culture media.
38
biofilms
- many bacteria formspecialized, surface-attached communities
- usually contain multiple species, and can form on a range of organic or inorganic surfaces.
- form and continue to grow when nutrients are plentiful.
- Once nutrients become scarce, individuals detach from the community to disperse in search for new sources of nutrients.
- in nature can take many different forms and serve different functions for different species.
- The formation involves chemical signaling between organisms.
39
steps in the formation of many kinds of biofilms
1. Attachment
2. Microcolonies
3. Exopolysaccharide (EPS) production - material that helps them stick together
4. Mature Biofilm
5. Dissolution and dispersal
40
Cell Differentiation
- Bacteria faced with environmental stress undergo complex molecular reprogramming that can include changes in cell structure.
Examples include:
- Endospores of Gram-positive bacteria
- Heterocysts of cyanobacteria
- Fruiting bodies of Myxococcus xanthus
- Aerial hyphae of Streptomyces
41
Endospores
Clostridium and Bacillus species can produce dormant spores that are heat resistant.
Starvation initiates an elaborate 8-hour genetic program that involves:
- An asymmetrical cell division process that produces a forespore and ultimately an endospore
- mother cell engulfs the forespore which is now surrounded by a cortex which protects it from heat
Sporulation can be divided into discrete stages based primarily on morphological appearance
42
Cyanobacterial Heterocysts
Allow this multicellular organism to fix nitrogen anaerobically in the heterocyst while maintaining oxygenic photosynthesis in vegetative cells
43
Fruiting Bodies
- Myxococcus xanthus uses gliding motility
| - Starvation triggers the aggregation of 100,000 cells, which form a fruiting body containing myxospores
44
Filamentous Structures
- Streptomyces bacteria, a major source of antibiotics, form mycelia and sporangia analogous to those of fungi
- As nutrients decline, aerial hyphae divide into spores that are resistant to drying
