8/29/15
Cells have many functions
To some extent, most cells have the ability to metabolize, digest
“food”, dispose of wastes, reproduce, grow, move, and respond to
stimuli from their environment
Cells have many functions
To some extent, most cells have the ability to metabolize, digest
“food”, dispose of wastes, reproduce, grow, move, and respond to
stimuli from their environment
How do they do this?
The details are complicated, and we will be learning about
them as we move through each organ system this semester
However…
The principles of membrane transport, protein synthesis and cell
reproduction that unite all of these cells
Movement of substances across a cell membrane
occurs in multiple “ways”
Most liquids we see in biology are solutions, which have two
components:
The solvent (the dissolving medium)
The solutes (what’s dissolved in the solvent)
Water is the most biologically important solvent:
Our intracellular fluid is a solution containing small amounts
of dissolved gases (oxygen, carbon dioxide, among others),
nutrients and salts, all dissolved in water
Our interstitial (aka extracellular) fluid contains nutrients,
hormones/neurotransmitters, salts and waste products
dissolved in water.
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Movement of substances across a cell membrane
occurs in multiple ways
The cell’s membrane is selectively permeable, meaning that some
substances pass through freely, while others do not
If things move through with no energy input from the cell, they
are moving through passively (this is passive transport)
If the cell provides metabolic energy (ATP) to move things
across its membrane, this is active transport
Molecules tend to move down a concentration
gradient
This is diffusion
Molecules tend to move down a concentration
gradient
As molecules move randomly (because of their inherent kinetic
energy), they tend to move from areas of high concentration
to areas of low concentration (i.e. down a concentration
gradient)
Simple diffusion is diffusion across a cell’s plasma membrane
It will occur if:
molecules are small enough to pass through
they can dissolve in the fatty portion of the membrane
there is a membrane carrier to assist them
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Molecules tend to move down a concentration
gradient
As molecules move randomly (because of their inherent kinetic
energy), they tend to move from areas of high concentration
to areas of low concentration (i.e. down a concentration
gradient)
Simple diffusion is diffusion across a cell’s plasma membrane
It will occur if:
molecules are small enough to pass through
they can dissolve in the fatty portion of the membrane
they are assisted by a membrane carrier
Osmosis is the diffusion of water through a selectively
permeable membrane through specialized water pores on the
cell’s membrane (aquaporins—’water pores’)
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Filtration occurs under pressure
There is no concentration gradient, rather there is a pressure
gradient
Things move from areas of high pressure to low pressure
Filtration occurs under pressure
There is no concentration gradient, rather there is a pressure
gradient
Things move from areas of high pressure to low pressure
In biology, the pressure tends to come from fluid, or hydrostatic
pressure:
This is still technically passive transport,
because it takes no input of energy by the
cell
Active transport requires ATP
Active transport usually results when:
solutes are too large to pass through the plasma membrane
unable to dissolve in the fatty core of the membrane
they have to move against a concentration gradient
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Sometimes things can’t pass through the
membrane
When this happens, they are moved across the membrane by
endo- and exocytosis
Mitosis occurs for many reasons
Growth, and repair of damaged cells are the primary reasons
that human cells undergo mitosis.
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Mitosis occurs for many reasons
Growth, and repair of damaged cells are the primary reasons
that human cells undergo mitosis.
Taking steps toward understanding
mitosis
The process is not difficult (I promise), but the
terminology can be:
Homologous chromosomes
Sister chromatids
Centromere
Daughter chromosomes
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Taking steps toward understanding
protein synthesis
There are a few concepts I want you to grasp:
The major steps: transcription & translation
Role of DNA
Role of RNAs
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