5. Transport Across Membranes
• Passive Transport: small, uncharged molecules move freely
across the plasma membrane
• Active
Transport:
Larger, charged
molecules need
help to get across
– requires energy
6. Passive Transport
• Passive Transport:
– Small, uncharged molecules move in and out of a cell
• water, carbon dioxide, ammonia, oxygen, fatty acids
– Molecules move both directions across the plasma membrane
– Net movement is down the concentration gradient
• Simple Diffusion
– directly through the
phospholipid bilayer
• Facilitated Diffusion
– with the help of channel or
carrier proteins
– proteins only let certain
molecules through
7. Active Transport
Active Transport
• Larger, charged molecules need the help of transport proteins to
get across
• Can go against concentration gradient
• Requires energy
Transport Animations
10. Nucleus
• Surrounded by a double
membrane
– called the nuclear envelope
• Contains chromatin
– loose DNA strands that form
chromosomes
– DNA & RNA hold "blueprints"
that build/regulate proteins
• direct all cell functions
• Pores in membrane allow
material to enter and leave
the nucleus
11. Nucleolus
• Dense mass of
RNA and proteins
inside the nucleus
• NOT bound by
membrane
• Ribosomes are
made here
• Sometimes more
than one
12. Ribosomes
• Ribosomes build proteins in a process called translation
– Two subunits (parts) work together
– mRNA feeds through, directing the sequence of amino acids
– amino acid are joined to form a polypeptide chain
Protein Synthesis Video
13. Ribosomes
• Build proteins by connecting amino acid chains
• mRNA gives
instructions
for specific
amino acid
sequences
• tRNA pieces
hold amino
acids and
match up with
mRNA to build
the protein
chain
14. Rough Endoplasmic Reticulum
Rough ER
• studded with
ribosomes
• Sorts & transports
proteins
• connected to
nuclear envelope
• Vesicles are pinched
off to transport
contents to Golgi or
outside of cell
15. Smooth Endoplasmic Reticulum
Smooth ER
• Makes lipids
– steroids, hormones
• Breaks down
carbohydrates, lipids
and toxins
• Vesicles pinch off
– transport contents to
Golgi or outside cell
• Liver, ovaries & testes
have LOTS of smooth
ER
16. Golgi Apparatus
• Looks like a stack
of pancakes
• Stores, sorts,
modifies and
packages proteins
• Molecules
transported to
and from the
Golgi by means of
vesicles
17.
18. Lysosomes
• Garbage disposal
of the cell
• Contain
hydrolytic
enzymes that
break down
wastes (old cell
parts as well as
invaders)
19. Mitochondria
• Site of Cellular Respiration (O2 is used, CO2 is given off)
• Food molecules (fats, protein, carbs) are converted into ATP
• Folds called cristae
increase surface
area & efficiency
of chemical
reactions
• Inner fluid is
called the matrix
• Has its own DNA
and ribosomes
20. Cell Wall
• Found in bacterial and plant (as well as algae) cells
• Located outside of the cell membrane
21. Cell Wall
• Rigid, protective barrier
composed of strong cellulose
fibers (polysaccharides) and
proteins
• Outermost lamella is a gluey
layer between adjacent cells
22. Chloroplasts
• Contain chlorophyll (green pigment)
• Inside the double membrane, granum are formed from stacks
of thylakoids (membrane-bound disks)
– this is where photosynthesis occurs (solar energy converted into carbs)
• Contains own DNA and replicates
independently from the rest of the cell
24. Intercellular Junctions
• Tight junctions bind cells together and prevent certain fluids
and molecules from crossing the membrane.
• Desmosomes
(plasmodesmata) are
strong anchors between
cells.
– made from folds of both
cells’ intertwined
membranes
• Gap junctions are formed
from proteins embedded
in the cell membrane.
– allow substances (and
electrical charges) to flow
in and out between cell.
25. Plasmodesmata
Gaps in a plant/bacterial cell wall that allow for
transportation of substances between cells
26. Peroxisomes
• Small sacks enclosed
in a single
membrane
• Contains enzymes
that break down
alcohol & fatty acids
• Formed from
pinching off from
the ER
• Found mostly in
kidney and liver cells
27. Cytoskeleton
• Microfilaments – thin,
contractile (stretchy) filaments
– help muscles cells contract
– pinches cells in two during cytokinesis
– provide strength, elasticity and
support to the cell’s cytoskeleton
• Microtubules – tiny, tube-like
structures
– form centrioles
– give rise to cilia and flagella
– limited transport capabilities
– give shape and support to cell’s
cytoskeleton
28. Centrioles
• Only in animal cells
• Hang out near the
nucleus
• Made from
microtubules
• Help divide
chromosomes during
cell division.
29. Cilia & Flagella
• Hair or tail-like structures
that provide motility
• Formed from microtubules
that arrange themselves
into a cylindrical shape
• Centrioles form basal
bodies that provide the
framework for each cilium
or flagellum
• Generally occur only in
animal cells
