These includes all the notes I have taken from the BMS1025 Cell Biology lectures 2018/2019 in my first year of undergrad. From the nucleus to the muscle tissues, these notes span the entirety of the module.
NUCLEUS
To keep cells organised, you require:
energy (1)
membranes (2)
(1) Energy
There are several different molecules that are basically packets of energy. Each molecule has one
or more high energy bonds that store energy that can be released:
1. Adenosine triphosphate, ATP
1. it is the main energy-storing molecule of cells
2. the energy is basically stored as/in phosphate bonds
1. breaking these bonds will release energy
2. the energy is used for energetically-unfavourable reactions (eg. active
diffusion)
3. when bonds are broken, resulting molecules would be:
1. Adenosine diphosphate (ADP)/adenosine monophosphate (AMP)
2. an inorganic phosphate
3. to regenerate ATP, energy from another source is required from another source
(REFER TO MITOCHONDRIA)
2. Guanosine triphospahte
1. very similar to ATP
2. the energy is stored as/in phosphate bonds, like ATP
3. used in certain processes (eg. translation, nuclear import, etc.)
4. used more as a signalling molecule [WHY IS GTP ONLY USED IN CERTAIN
PROCESSES, NOT EVERYTHING LIKE ATP?]
3. Nucleotide-sugars
1. are activated forms of monosaccharides, such as glucose, fructose and galactose
2. eg. UDP-N-acetyl glucosamin (pic), NADH, NADPH, FADH2, Acetyl CoA
3. structure of nucleotide-sugar: similar to ATP but the last phosphate is replaced
with sugar
4. the energy is stored in:
1. phosphate bonds
2. sugar-phosphate bonds
(2) Membranes (phospholipid bilayer)
Phospholipids are amphipathic
which means they have both hydrophobic and hydrophilic heads
These phospholipids spontaneously rearrange themselves in bilayers (in water)
bilayers are the lowest free-energy configuration (molecules will always try to be in the
most stable configuration)
hydrophobic regions find ways to remove themselves from water
hydrophilic regions interact freely with the water
These bilayers then also spontaneously form sealed compartments
which is energetically-favourable
prevents any of the hydrophobic heads from interacting with the water
, (if it were just one sheet, water is able to enter from the sides)
like a micelle BUT NOT A MICELLE (which are formed from fatty acids)
Membrane proteins
These are proteins which interact with, or are part of, biological membranes
1. integral proteins
1. these proteins are permanently-attached to the membrane
2. these are the only class of proteins which perform functions both inside and
outside of the cell
3. functions:
1. transporters
2. channels (eg. potassium channel)
3. linkers
4. receptors
5. etc
4. there are different types of integral membrane proteins:
1. single pass (which passes through the membrane only once)
2. multiple pass (which passes through the membrane multiple times)
3. embedded in one leaf ?????????
4. covalently-attached to an embedded lipid (via an oligosaccharide linker)
(eg. N-linked glycosylation in the ER)
2. peripheral proteins
1. these proteins are attached loosely to the membrane
2. these proteins interact with:
1. an embedded protein, OR
2. phospholipid polar heads (reversible) ??????????
3. functions:
1. gives support
2. communication
3. as (simple) enzymes
4. for molecule transfer
~ Passage across the phospholipid bilayer (different ways)
Passive diffusion (1)
Osmosis (2)
Facilitated diffusion (3)
Active diffusion (4)
(1) Passive diffusion
molecules are free to move across the bilayer
movement down a concentration gradient *
only for small and/or non-polar molecules
o eg. oxygen, carbon dioxide, lipophilic drugs
(2) Osmosis
water molecules passively move across the membrane
movement down a concentration gradient *
only for water molecules
,(3) Facilitated diffusion
molecules move across the membrane via:
o channels (faster), or
o carriers (slower)
movement down a concentration gradient *
for all other molecules that are too large or are polar, thus unable to pass through via
passive diffusion
(4) Active transport
molecules move across the membrane via 'pumps'
movement across a concentration gradient **
for all other molecules that are too large or are polar, thus unable to pass through via
passive diffusion
There are two types of active transport:
ATP-driven transport (primary transport)
Coupled transport (secondary transport)
o Symport (two molecules transported in the same direction at the same time)
o Antiport (two molecules transported in opposite directions at the same time)
Active transporters linked to an energy source allow accumulation to occur
NOTES:
Movement down a concentration gradient:
high to low concentration
energetically favourable (no energy needed)
spontaneous (until equilibrium is reached)
*Movement across a concentration gradient:
low to high concentration
energetically unfavourable (requires energy)
Cystic Fibrosis (mutation of CFTR in recessive genes) - CFTR, chlorine gated channels
(facilitated diffusion) that permit passive chloride movement across the apical membrane of
the epithelial cells in the lung
~ What is a nucleus?
a double membrane supported by a fibrous protein mesh
the aqueous solution of a nucleus contains:
o genetic material (DNA)
o RNA
o Proteins
~ Why do we need a nucleus?
the nucleus separates fragile chromosomes from the cytoskeletal/cytoplasmic filaments
the nucleus also separates RNA transcription (in the nucleus) from the translation
machinery (within the cytoplasm outside of the nucleus)
, o able to regulate the export of RNA
o able to regulate the export of other proteins
o able to carry out alternative splicing by processing DNA in the nucleus
~ Possible evolution of the nucleus
Starts from Bacillus subtilis (ancient prokaryotic cell)
1. DNA attached to the cell membrane at several points
2. The membrane invaginates to form mesosomes (invaginations of the membrane)
3. Repeated invagination (formation of mesosomes) led to the formation of a nucleus
Ancient prokaryotic cell evolved to eukaryotic cell
Deoxyribonucleic Acid (DNA)
DNA is a double helix, made out of a sugar-phosphate backbone with pairs of bases protruding
in the middle
~ How do they store information?
They store information due to their ability to form complementary nucleotide base pairs via
hydrogen bonding
T - 2 hydrogen bonds - A
C - 3 hydrogen bonds - G
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