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Cell communication and Energy in Biology
5/30/12
Cell-Cell Communication
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Signals sent to other cells
Three levels
– Direct contact
– Local
• Paracrine
• Synaptic
– Long distance
• Endocrine
The Three Stages of Cell Signaling
– Reception
– Transduction
– Response
Reception: A signal molecule binds to a receptor protein, causing it to change shape
• The binding between a signal molecule (ligand) and receptor is highly specific
• A shape change in a receptor is often the initial transduction of the signal
• Most signal receptors are plasma membrane proteins
Transduction: Cascades of molecular interactions relay signals from receptors to
target molecules in the cell
• Signal transduction usually involves multiple steps
• Multistep pathways can amplify a signal: A few molecules can produce a large cellular
response
• Multistep pathways provide more opportunities for coordination and regulation of the
cellular response
Nuclear and Cytoplasmic Responses
• Ultimately, a signal transduction pathway leads to regulation of one or more cellular
activities
• The response may occur in the cytoplasm or may involve action in the nucleus
• Many signaling pathways regulate the synthesis of enzymes or other proteins, usually
by turning genes on or off in the nucleus
• The final activated molecule may function as a transcription factor
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Biological Energetics
How cells obtain and energy needed for survival
Two types of organisms
– Autotrophs
– Heterotrophs
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Net loss of energy as it is transferred through organisms
Autotrophs
Are able to synthesize macromolecules by using small molecules from environment
– Do not consume other organisms to obtain molecules
Vast majority are photosynthetic
– Use energy from sunlight to power anabolic reactions
All biological energy originates with autotrophs
– Life is solar powered
Heterotrophs
Consume other organisms and utilize energy obtained from catabolic degradation of
macromolecules
– Rely on the presence of autotrophs as original energy source
– Loss of energy in transfer means that the balance between heterotrophs and
autotrophs is crucial
Can consume autotrophs or other heterotrophs
Saprophytes-consume dead organisms “decomposers”
– Bacteria, fungi, scavengers
Photosynthesis and respiration
Photosynthesis is the use of solar energy to power anabolic reactions-autotrophs
Respiration is the process in which macromolecules are degraded to obtain cellular
power-heterotrophs
They are complementary processes
– One relies on the products of the other and they are linked biologically
Photosynthesis
Takes place in the chloroplasts of plants and in the cytoplasm of photosynthetic
bacteria
Requires CO2 and a source of Hydrogen
– Usually water but can be H2S
– Ultimately results in Glucose and Oxygen production (water also)
– CO2 +6H2O +Light energy--->C6H12O6 + 6O2
• Oxygen production by plants is essential for other life to exist
Photosynthesis 2
Actually two stages in Photosynthesis
– Light cycle-Sunlight is used to synthesize ATP and other energy storing molecules
• Made up of Photosystems I and II
– Calvin Cycle or Dark Cycle-Energy from ATP and other molecules is used to
synthesize sugars
Chloroplasts
• Light reactions happen in Thylakoids of Granum
• Calvin cycle happens in Stroma
– Chlorphyll is the molecule that catches solar energy in chloroplasts
– Other chromoplasts exist that contain different molecules for catching solar energy
Why are chlorplasts green?
• Absorbs Red and Blue light
• Green light is transmitted or reflected making plants appear green