Extracellular components and connections between cells help coordinate cellular activities
Most cells synthesize and secrete materials that are external to the plasma membrane
These extracellular (outside plasma membrane) structures include
Cell walls of plants- major structural component of plant cells made of cellulose, also found in prokaryotes, protists and fungi (peptidoglycan)
Cell wall protects the plant cell, maintains its shape and prevents excessive uptake of water
Plant cell walls are made of cellulose fibers embedded in other polysaccharides and proteins
Layers
Thin Flexible Primary Cell Wall
Thick Secondary Cell Wall
In between plasma membrane and primary wall gives structural integrity
Middle lamella - material between cell walls
Plasmodesmatagaps in cell wall allowing for communication and movement of things between plant cells, rigid cell walls are restrictive unlike permeable membranes
Extracellular matrix (ECM) of animal cells instead of cell walls
Series of glycoproteins such as collagen (major), proteoglycans, and fibronectin make up ECM
Fibronectin connects collagen to integrin
Proteoglycans perform adhesion (glue)
Proteins bind to receptor proteins in the plasma membrane called integrins
Functions
Support
Adhesion
Movement
Regulation
Intercellular junctions physically connect cells, adhere interact or communicate through direct contact
Types
Plasmodesmatagap-like channels that perforate cell walls
Tight Junctions membranes of neighboring cells are pressed together preventing leakage of extracellular fluid in between cells (in stomach)
Desmosomes (anchoring junctions) fasten cells together into strong sheets--strongest function (muscle cells)
Gap junctions (communicating junctions) provide cytoplasmic channels between adjacent cells (heart cells), enable multiple cells to act as one
Photosynthesis
The most important reaction in all of nature, makes food
Converts solar energy into chemical energy
Directly and indirectly nourishes all living things
Autotrophs/Producers - organisms that produce their own food through photosynthesis
Algae (protist, eukaryotic organism), plants, cyanobacteria - first living organisms to perform photosynthesis
Heterotrophs/Consumers - must eat in order to obtain energy, eating products of photosynthesis
Opposite of cell respiration (which is exergonic, produces ATP), photosynthesis is endergonic
Water is oxidized to O2, CO2 is reduced → glucose
Photosynthetic part of a plant (organ): Leaf
Holes in leaf: stomata, where water evaporates (transpiration) and CO2 enters and O2 leaves
Creates transpirational pull from roots
Xylem are cells that water travels through
Plants want water to evaporate out of the plants, no transpirational pull without evaporation
Plant would dehydrate if too much water evaporated, need to balance transpiration
Increase transpiration and dehydration
Heat (temperature)
Dryness (humidity)
Wind
PHOTORESPIRATION
STOMATA CLOSE to balance out environment with the guard cells
Calvin Cycle cannot occur (no CO2) can’t make sugar
RuBisCo can ALSO fix O2 to RuBP in place of CO2 → cant produce G3P
Wastes NADPH and ATP
C3 Plants make 3-Carbon compound, PGA in the calvin cycle
C4 Plants live in dry conditions (midwest), have adaptations to prevent photorespiration → STORE CARBON DIOXIDE
Doesnt matter if stomata are closed or open
Used stored CO2,
C4 Plant
Uses enzyme PEP Carboxylase → pulls in CO2 stores carbon as 4 carbon molecule Oxaloacetate
Calvin cycle takes place in Bundle-sheath cell, but still have mesophyll cells
CAM Plant - the extremes (cacti, desert plants)
Store carbon as crassulacean acid, organic acid
CAM Plant opens stomata at night (when it cools down)
More stomata on bottom, if more on top plant would dehydrate
Guard cells: flank stomata, control if stomata are open, closed, where gasses enter and leave, (O2/CO2), water can evaporate out of the stomata → transpiration (transpirational pull)
Mesophyll- part of a leaf that contains lots of photosynthetic cells
Cells contain chloroplast - double membrane, inside are pancake shaped discs called thylakoids, and stacks of thylakoids = granum
Fluid in membrane outside thylakoids called stroma
Two reactions:
Light Reactions - light (photo) inside the thylakoids
NADP+ and ADP + P, take H2O and oxidize it, produce NADPH, and ATP, O2 as a byproduct,
Light to make ATP - photophosphorylation
Calvin cycle (The Dark Reactions)- synthesis (builds molecule) inside stroma
Major reactant in cycle: CO2 reduced and given electrons/protons, creates glucose, given by NADPH gives CO2 the electrons/protons. Electrons - energy
Powered by ATP
Purpose of producing glucose?
Glucose is used for everything:
Sugar → cell respiration, used to make ATP to grow plant
Sugar = structure, cellulose (long chain of glucose)
Sugar = energy storage, starch
Light - electromagnetic radiation
Shorter wavelength -- high energy (UV, gamma, X ray)
Longer wavelength -- low energy (infared microwaves, radiowaves)
Different colors correspond with different wavelengths, visible light in the middle of spectrum
Chlorophyll a is the main photosynthetic pigment
Accessory pigments such as chlorophyll b broaden the spectrum used in photosynthesis
Xanthophylls - yellow
Carotenoids - orange
Reflect (bounce off) vs Transmitting (go through)
No light is absorbed by cell
Green light cannot be used by plant, would die
Plants absorb red and blue light the best
Color of sky depends on molecular composition of atmosphere
Spectrophotometer - put sample of light in, tells level of transmittance or absorption
Shoot green light through chlorophyll, high transmittance (low absorption)
Shoot blue light through chlorophyll, low transmittance (high absorption)
Absorption Spectrum - graph plotting a pigment’s light absorption versus wavelength
Larger spectrums,
Action Spectrum - profiles the relative effectiveness of different wavelengths of radiation in driving a process, totality of spectrums
Pigment - molecule that will absorb or reflect a wavelength
Color determined by what it reflects
Trees go dormant in winter, chlorophyll dies, only see carotenoids and xanthophylls (yellow + orange), not enough sunlight
Engelmann’s Experiment
Grew algae under different wavelengths
Grew aerobic bacteria on top of the algae, large growth on opposite sides of spectrum, none in green because algae isn’t photosynthesizing there
Plants not black because would absorb every wavelength, overheat, proteins denature
Chlorophyll has a Magnesium center (a vs. b has difference of one func. group)
Mg holds on to electrons, electrons from water and NADPH
Accepts unit of light - photon, excites electron, gives power to electron
Cellular Respiration
Alcohol fermentation (yeast)
Pyruvate converted to ethanol (2 carbon, releases CO2)
Brain cells = purely aerobic
Obligate anaerobes = die in the presence of O2 (bacteria), carry out fermentation/anerobic respiration
Denitrifying bacteria
Anaerobic respiration: use sulfates as final electron activity instead of O2 and substrate level phosphorylation not the electron transport chain
Glycolysis
Oldest process
Before mitochondria, glycolysis took place
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Unit 3: Cellular Energetics