HUMB1000 Lecture 5: 5 - Energy Process
12 Jun 2018
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Diffusion
• Molecules are in constant random motion due to their kinetic energy
• Dissolved molecules become evenly distributed throughout the solution
• Move from high to low concentration
• Rate of diffusion is determined by: temperature, size of molecules, and steepness of
the concentration gradient
Facilitated Diffusion
• A special carrier protein with a central channel helping molecules move across the
membrane
• Only binds to a specific molecule – a sugar or amino acid
• Once bound to the carrier protein, the protein changes shape moving the molecule
down its concentration gradient through the membrane
• Passive process moving molecules from high to low concentrations
• Works in both directions – in and out of the cell
Osmosis
• Most polar molecules – sugars and proteins CANNOT freely move across the lipid
membrane
• Although water is polar – they are small enough to pass through the membrane
freely
• Molecule such as urea will not be able to diffusion across the membrane – large and
polar. Urea being a polar molecule will interact with other polar molecules, fewer
free water molecules → lower concentration gradient
• Water molecules are moving into area with urea, and a rise in volume
❖ Isotonic – osmotic concentrations of two solutions are equal
❖ Hypertonic – higher concentration of solutes
❖ Hypotonic – lower concentration of solutes
Active Transport
• Example: sodium-potassium pump – 3 sodium ions bind to the protein channel and
ATP provides the energy to change the shape of the channel
• 1 phosphate group from the ATP remains bound with the channel
• 3 sodium ions are released on the other side of the membrane outside of the cell. 2
potassium ions bind to the channel
• Binding of the potassium ions causes the channel to change shape releasing into the
cytoplasm
• Moves against the concentration gradient – low to high
• Active process – requires energy
Haemolysis and Crenation
• Erythrocytes – red blood cells: thrives in isotonic solution
• Hypertonic – red blood cells shrivel and becomes crenated
• Hypotonic – red blood cells swell and burst and becomes hemolysis
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Glycolysis
• Derives energy from the oxidation of nutrient – glucose.
• Glycolysis - oxidation of glucose to pyruvate
• Energy released during these oxidation reactions is used to form adenosine
triphosphate (ATP)
• Addition of 2 phosphates to the glucose molecule, at the expense of two molecules
of ATP
• 6-carbon sugar diphosphate molecule and 2 low energy adenosine diphosphate
molecules or ADP
• 6-carbon sugar diphosphate molecule is then split into two 3-carbon molecules
• Each of the 3-carbon molecules is converted through a series of steps, to pyruvate.
During these reactions, electrons are transferred to the co-enzyme NAD+ to form
NADH and ATP is formed
• Under aerobic conditions, the pyruvate is further oxidized to yield more ATP and
under anaerobic conditions, the pyruvate is converted into lactic acid
Citric Acid Cycle
• During glycolysis, glucose is broken down to pyruvate
• Two-carbon fragment of pyruvate is used to form acetyl-CoA. The acetyl-CoA enter
the Krebs cycle, which occurs in the mitochondrion
• During the conversion of pyruvate to acetyl-CoA, carbon dioxide is produces and a
molecule of NADH is formed
• Two-carbon acetyl portion of the acetyl-CoA is transferred to a 4-carbon molecule,
producing a 6-carbon compound. The CoA carrier molecule is released
• Carbon dioxide is then released from the 6-carbon molecule, forming a 5-carbond
compound. In this step, hydrogen is removed and transferred to NAD+ to form NADH
• A second oxidation and decarboxylation occurs. Again NADH and carbon dioxide are
produced. In addition, a molecule of ATP is produced. As a result of these reactions,
a 4-carbon molecule is forme in the Krebs cycle
• Finally, the 4-carbon molecule is further oxidized and the hydrogens that are
removed are used to form NADH and FADH2. These reactions regenerate the 4-
carbon molecule that initially reacts with acetyl-CoA
• Each glucose molecule is broken down into two pyruvate molecules during
glycolysis. Then each pyruvate is converted to acetyl-CoA, which enters the Krebs
cycle
• Thus, for each glucose molecule, the Krebs cycle must complete two circuits to
completely break down the two pyruvate molecules
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Electron Transport Chain and ATP Synthesis
• When glucose is oxidized during glycolysis and the Krebs cycle, the co-enzymes NAD+
and FAD are reduced to NADH + H+ and FADH2
• In the mitochondria, the electrons from NADH + H+ are transferred to the electron
carrier proteins, and the protons are transferred across the membrane
• As the electrons move from cytochrome to cytochrome, down the electron
transport chain, ore protons are carried across the membrane
• Cytochrome � transfers electrons to the cytochrome � oxidase complex. Protons are
also transferred to the outside of the membrane by the cytochrome � oxidase
complex
• The cytochrome oxidase complex then transfer electrons from cytochrome � to
oxygen, the terminal electron acceptor, and water is formed as the product
• The transfer of protons generates a proton motive force across the membrane of
the mitochondrion
• Since membranes are impermeable to ions, the protons that re-enter the matrix
pass through special proton channel proteins called ATP synthase
• The energy derived from the movement of these protons is used to synthesize ATP
from ADP and phosphate. Formation of ATP by this mechanism is referred to as
oxidative phosphorylation
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Document Summary
Urea being a polar molecule will interact with other polar molecules, fewer free water molecules lower concentration gradient: water molecules are moving into area with urea, and a rise in volume. Isotonic osmotic concentrations of two solutions are equal. Active transport: example: sodium-potassium pump 3 sodium ions bind to the protein channel and. Atp provides the energy to change the shape of the channel: 1 phosphate group from the atp remains bound with the channel, 3 sodium ions are released on the other side of the membrane outside of the cell. 2 potassium ions bind to the channel: binding of the potassium ions causes the channel to change shape releasing into the cytoplasm, moves against the concentration gradient low to high, active process requires energy. Haemolysis and crenation: erythrocytes red blood cells: thrives in isotonic solution, hypertonic red blood cells shrivel and becomes crenated, hypotonic red blood cells swell and burst and becomes hemolysis.
