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Chapter 3
SIMILARITIES AND DIFFERENCES BETWEEN
CELLS
Life Must Be Dynamic
Selectivity
• We are a community of living creatures (cells) in a “pond of water”– Specialized members of the community– Outlaw cells (cancer)– Invaders
The Cell, The Smallest Living Unit
Specialization in the Society
Blood Stream
Each group of cells have unique barriers (capillaries) for exchange with the blood which allows them to create a special environment for that group of cells
Different Cell Types
• Common Processes: Processes all cells must do.
• Qualitative Differences: Unique processes that all types of cells do not do
• Quantitative differences: Some cells do more or less of some processes
Energy
• The production of high potential energy molecules such as ATP
• All cells need to do this
Cell Types Differ in their use of Energy
Glucose + 2 ADP + 2 Pi + 2 NAD+ ---> 2 Pyruvate + 2 ATP + 2 NADH + 2 H+ + 2 H2O
Small amount of energy (ATP)
Acetyl-CoA + 3 NAD+ + FAD + GDP + Pi + 3 H2O ---> 3 NADH + FADH2 + CoA-SH + GTP + 3 CO2
Large amount of energy
Without Oxygen
With OxygenUse of Fat and pyruvate
Use of Sugar
Variation in energy
Extremes in energy use
Skeletal muscle
.
.
.
.
Brain
Reproduction (Stem Cells)
• Skin and lining of digestive system (replacement)
• Liver and muscle (damage)• Immune system (replacement
and attack)• Nervous system ???
Cell Division (proliferation)
• A complex process involving many reactions (proteins)
• Signals for and against– Inhibition– Stimulation
Copy DNA (check for mistakes: repair or apoptosis)
Mutations: mistakes that escape
Separate into two cells
Protein Synthesis and Degradation
• Both Carried out by proteins
• Synthesis depends on mRNA
• Degradation depends on proteins
• Highly controlled and selective
Turnover
The Cell Membrane
• Charge barrier
• Molecular ports (channels)
• Information ports (receptors)
• They often work together
The cell
Channels
Ion channel
Glucose channel
Relationships between Cells
• Communications: a language of chemical messages
• Coordinates functions involving many cells
• Signals and Receptors: A cell can’t respond to a signal that it can’t see
Signals
• Chemical messages made by one cell that gives directions to another cell or cells
• Two types: water soluble and fat soluble– Insulin – Glucocorticoids
Frequency and intensity modulated signals
Every hormone is a different “voice” talking to
those cells in the community that can listen
Receptors
• A cell can only respond to the “voices” that it can hear
• Receptors mediate many things– Open channels through the membrane– Alter gene expression– Signals often cascade and feedback
Receptors
Receptors
• Respond to the signal
• Adjust and remember
• Tolerance
• Dependence
Other Forms of Life in the Community
• Viruses
• Bacteria
• Fungi
• Parasites