Transcript Topic 1.3-1.6 The Cell

IB BIOLOGY
Topic 1 Cell Biology
1.3-1.6
Membrane Structure
• 1915- scientists knew
structure of membranes
included proteins and lipids.
• Davson and Danielli Model
1935
– Lipid bilayer model
– Covered on both sides with
thin layer of globular protein
• Singer and Nicholson 1972
– Proteins are inserted into
phospholipid bilayer, not
covering it
• Current model– Fluid mosaic model
Phospholipids
• Composed of:
– 3C glycerol
– 2 glycerol carbons have fatty
acid tails
– 3rd C attached to highly polar
organic alcohol bound to a
phosphate
– Hydrophobic and hydrophylic
regions
– Fatty acid tails not strongly
attracted to each otherallows for fluidity
– Structure maintained by
hydrogen bonding among
H2O molecules
Cholesterol
• Membranes consistency
of olive oil
• Various locations in fatty
acid tail region,
cholesterol molecules are
embedded
• Determine fluidity of cell,
temperature dependent
• Allows function during
wide temperature range
Proteins
• Create extreme diversity
in membrane function
• Embedded in bilayer
• Two Types:
– Integral protein
• Amphipathic- has both
hydrophobic and
hydrophylic portions
– Peripheral protein
• Bound to membrane
surface
• Can be anchored to
integral
Membrane Protein Functions
• Hormone binding- specific
shapes
• Enzymatic action- catalyze
chemical reactions
• Cell adhesion-permanent or
temporary connection
• Cell-cell communication-many
have carbs attached
• Channels for passive
transport- down the
concentration gradient
• Pumps for active transportneeds ATP, up the
concentration gradient
Membrane Transport
• Passive transport
– No ATP used
– Goes with concentration
gradient (Hi to lo)
• Diffusion: membrane
– Gases: O2 diffuses into a cell,
CO2 diffuses out
• Facilitated diffusion:
– Uses carrier proteins
• Osmosis:
– H2O across semi-permeable
membrane
– Solute and solvent ratio
important
Membrane Transport
• Size and Charge of
Molecules:
– Small, non-polar cross
easily
• CO2, O2, N2, H2O,
glycerol
– Large, polar cross with
difficulty
• Cl-, K+, Na+, glucose,
sucrose
Membrane Transport
• Active transport:
– Uses ATP
– Goes against the
concentration gradient
• Animal cells have higher
K+ concentration inside
than outside, and have
greater Na+
concentration outside
than inside
• Balanced maintained by
sodium-potassium
pump
Membrane Transport
• Endocytosis
– Fluidity dependent
– Allows macromolecules
to enter cell
– Part of plasma
membrane pinched off
to enclose
macromolecule
– Changes shape of
membrane
– Creates vesicle that
enters cell
Membrane Transport
• Exocytosis
– Reverse of endocytosis
Specialized Transport
• Pinocytosis- intake of
extracellular fluids
• Phagocytosis- intake of
large particulate matter
– Ex. Macrophage
engulfing antigen
Cell Division
• The Cell Cycle:
– Describes the behavior of
cells as they grow and
divide.
– Interphase: G1, S, G2
– G1-smallest cell will ever
be, major event is growth
– S- replication of cellular
DNA
– G2-organelles increase in
number, DNA begins to
condense from chromatin
 chromosomes,
microtubules begin to
form.
Cell Division
• Cyclins:
– Proteins that control
cell’s progression
through cell cycle
– Bind to cyclin-dependent
protein kinases (CDKs)
enabling them to act like
enzymes
– Cause cell to go from
G1S G2M
– Can pause during G1 and
enter G0- a non-growing
phase
• Time remaining in this
phase varies
– Nerve and muscle cells
do not progress past G0
Mitosis
• M phase:
– Replicated chromosomes
move to opposite poles
of cell
– Cytoplasm divides
– Result: identical
daughter cell
• Phases of Mitosis:
–
–
–
–
Prophase
Anaphase
Metaphase
Telophase
Chromosome
• Before replication in S
phase, cells have 1
molecule of DNA
• After- 2 molecules of DNA
held on center by
centromere
• Condensation of DNA:
– Super-coiling
– DNA wraps around histone
proteins- “nucleosome”
– Nucleosomes solenoid
chromosome
Prophase
• The chromatin fibers
become more tightly coiled
• The nuclear envelope
distinegrates, nucleoli
disappear
• Mitotic spindle forms
• Centromere of
chromosomes attach to
spindle fibers by
kinetochores
• Centrosomes move to
opposite poles of cell
lengthening the
microtubules
Metaphase
• Chromosomes move to
the middle of the cell.
• Centromere of
chromosomes lie on the
plate.
• Movement of
chromosomes
controlled by spindle
• Centrosomes at
opposite poles
Anaphase
• Shortest phase of mitosis
• Chromosomes move to
opposite parts of the cell.
• Movement due to
shortening of the
microtubules of spindle
• Centromeres attached to
microtubules, so they
move first
• Result: each pole has
complete, identical set of
chromosomes.
Telophase
• Chromosomes are at
each pole
• Nuclear membrane
begins to reform
• Chromosomes
chromatin
• Spindle disappears
• Cell elongates, ready for
cytokinesis
Cytokinesis
• Cleavage of animal cell
• Cell plate formation in
plant cell
https://www.youtube.com/watch?v=ofjyw7AR
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https://www.youtube.com/watch?v=ZEwddr9
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Cancer
• Uncontrolled cell
growth
• Primary tumor:
– Occurs at original site of
cancer
• Secondary tumor:
– Metastatic- has spread
from original site to
another location
– Can be found in many
locations
Henrietta Lacks and HeLa Cells
• http://www.cbsnews.com/news/the-immortalhenrietta-lacks/
• Henrietta Lacks was an African American woman
who died in 1951 of cervical cancer.
– Her cancerous tumor cells were of interest to doctors,
because they were the first cancer cells that would
grow under laboratory conditions. The cells have been
studied and cultured world- wide for decades without
her knowledge, permission, or family compensation.
– She is the most important contributor to cancer
research to date.
Cancer, cont.
• Reasons for formation
of primary tumors:
– Gene mutation
– Abnormally high gene
expression
– Oncogenes:
• Section of genes that
contributes to conversion
of normal cell cancer
cell
• Oncogenes:
– Can mutate in response
to environmental trigger
• Ex: Cigarette smoke