Chapter 2: Cell Physiology
Observations of Cells
- Larger species have a greater number of cells but not larger ones
o Muscle cells are the largest in the body, then red blood cells, digestive tract lining
(epithelial) cells and live cells
- Cell are the smallest structural and functional unit capable of carrying out life processes
o Functional activities of each cell depend on specific structural properties of the
cell
- Cells are living building blocks of all plant and animal organisms
o An organisms structure and function ultimately depend on the individual and
collective structural characteristics and functional capabilities of cells
- All new cells and new life arise only from pre-existing cells
o Continuity of life; everything comes from cell division, life cannot come from
something nonliving
An Overview of Cell Structure
- There are about 200 different cell types in the human body
o There is no such thing as a typical cell however cells share many common
features
3 major subdivisions:
Plasma membrane encloses the cell
Nucleus contains the DNA (there can be multiple)
Cytoplasm consists of various organelles, structural proteins,
transport/secretory vesicles, enzymes and the cytosol (part of the
cells interior not occupied by the nucleus)
Ribosomes and mitochondria are common to many cells; vary in amount
and volume
o A series of common components are directly associated with force generation
with in cells (more specific to muscle cells)
Regulatory proteins troponin and tropomyosin
Contractile proteins actin and myosin
Structural proteins titin, nebulin and desmin
Cellular Metabolism
- Intermediary metabolism the large set of chemical reactions inside the cell that involve
the degradation, synthesis and transformation of small organic molecules (simple sugars,
amino acids, fatty acids)
o Necessary for capturing energy that is required for cell activities, providing raw
materials needed to maintain a cells structure, function and for cell growth
o Occur in the cytoplasm (mostly in the cytosol where thousands of enzymes can
help with these processes)
- Cells participate in (simultaneously; at an equal or unequal rate, depending on the
demands of the cell):
o Anabolic processes favour the synthesis of molecules for building up organs and
tissues Sometimes molecules must be transported from outside the cell in order
for this to happen
Requires energy to combine simple molecules to build more complex ones
o Catabolic processes favour the breakdown of complex molecules into more
simple ones
This generates energy
- Source of energy for the body is chemical energy stored in the carbon bonds of ingested
food
o This energy must be extracted and converted into a usable form
High energy phosphate bonds of ATP (main E source of the body, a
nucleic acid)
Energy in released when the bonds holding ATP together are
broken
ATP ADP + P + E ior use by the cell
ATP = adenosine + 3 phosphate groups
Pathways for Production of ATP (see YouTube videos listed on pg. 85 of course kit)
- Substrate-level phosphorylation (in skeletal muscle):
o Creatine phosphate (CP) is the first energy source tapped at the onset of
contractile activity
Is stored in the cytosol, not the mitochondria
Contains a high-energy phosphate group
CP + ADP creatine kinaseatine + ATP
Reaction is reversible; CP can be used to make ATP and vice versa
Happens rapidly (less than a second) because it is a one-step
enzymatic reaction
There is 5 times as much CP as ATP in a resting muscle
Use to replenish ATP when the muscle starts to vigorous contract
o CP levels decrease more (see large changes) than ATP
levels (see minimal changes)
- Glycolysis:
o Occurs in the cytosol of the cytoplasm
o Consists of 10 separate reactions that breaks down glucose (a 6 C sugar molecule)
into 2 pyruvate acid molecules (3 Cs each)
Some of the energy from the breakdown of the covalent bonds in\ glucose
is used to convert ADP to ATP
Not efficient to support the demands of the body; net E extraction
= 2 ATP/glucose molecule
o Most of the energy is locked in the bonds of the pyruvate
acid molecules
Where mitochondria comes in to play
o End product available for further energy extraction 2 pyruvate molecules
o Can be an anaerobic OR an aerobic process
o Numerous metabolic diseases affect glycolysis
Problems with enzymes during glycolysis Ex: McArdle Disease cant break glycogen down into glucose;
no energy production
Due to absence of phosphorylase needed in the first step of
glycolysis
- Mitochondria and ATP production:
o Mitochondria are the energy organelles
Enclosed by a double membrane
Inner folded membrane is called the cristae
Contains enzymes required for the citric acid cycle and the electron
transport chain
Play a major role in generating ATP
o 3 primary pathways used to produce ATP from food:
Glycolysis (cytoplasm)
Krebs cycle (mitochondria matrix)
Electron transport chain (mitochondria inner membranes cristae)
o Energy stored in ATP is used for synthesis, transport and mechanical work
More energy is generated in aerobic conditions than anaerobic ones
- Tricarboxylic acid/citric acid/Krebs cycle:
o Occurs in the mitochondria
o Pyruvic acid from glycolysis enters the mitochondrial matrix and is catalyzed into
Acetyl CoA releases CO ,2generates NADH (2 molecules, one for each
converted pyruvic acid molecule)
Acetyl CoA enters into the tricarboxylic acid (TCA) cycle
CO 2oves out of the mitochondria, out of the cell, into the blood then
lungs and is released during exhalation
ATP is generated via aerobic metabolism (requires oxygen)
o Consists of 8 separate reactions that are directed by enzymes of the mitochondrial
matrix (inside the membrane)
o Key purpose of TAC: to produce hydrogen atoms for entry into the electron
transport system
These hydrogen atoms are caught by hydrogen carrier molecules:
NAD (derivative of B vitamin niacin) and FAD (derivative of B
vitamin ribolflavin)
o Transferring of the H generates NADH and FADH 2
End product available for further energy extraction
8 NADH and 2 FADH 2
o Is called a cycle because the end and starting molecules are identical (acetyl CoA)
o Indirectly produce ATP
GDP + P i GTP; GTP + ADP ATP + GDP
1 ATP/Acetyl CoA
1 glucose yields 2 Pyruvate, which yields 2 Acetyl CoA
o 2 net ATPs in TCA/1 entry glucose into glycolysis
- Electron transport chain:
o Requires oxygen
o Series of reactions that occur on the inner mitochondrial membrane
o Major source of ATP needed for cellular activities o There are a series of electron carrier molecules on the cristae of the inner
membrane of the mitochondria
These extract electrons from the NADH and FADH molecu2es from the
TCA
Where the most energy is produced
These electrons are eventually passed to O 2
o Oxidative phosphorylation (because oxygen is used in the final steps of energy
conversion)
Also called the respiratory chain because it is crucial to cellular respiration
(the intracellular oxidation of nutrient derivatives)
o Oxidative process occurs in small controlled steps:
The high-energy electrons extracted from NADH and FADH are 2
transferred from one electron carrier to another
The NADH and FADH are co2verted to NAD and FAD, which recycle
back to glycolysis and the TCA cycle pick up more H atoms
The high-energy electrons fall to successively lover energy levels as they
are transferred from carrier to carrier through the electron transport system
This releases energy that is then used to pump H from the matrix
t
More
Less
