The Cell

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The Cell

• Chapter 6

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Cell Size
Why are cells small?

• Most cells are relatively small because as
  size increases volume increases much more rapidly
  than surface area.

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• As cells get bigger they need more O2 and raw
  materials and need to export more waste products.
• The actual amount of cell membrane needed this
  exchange is less relatively speaking as the cell
  gets bigger.
• This is why most cells are microscopic. This is
  the optimal size for exchange with the
  environment.
• RLE (Real life example) Think how long it takes
  to exit the Foxboro High School parking lot after
  school versus exiting Gillette Stadium after a
  football game.

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Examples

• Some cells increase surface area relative to
  volume because their main job is exchange with
  the surrounding environment
• Root hairs
• Villi of small intestine

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Prokaryotic cells vs Eukaryotic cells

• Eukaryotes
• Have nucleus
• Have all organelles that prokaryotes plus
  membraneous organelles

• Prokaryotes
• No nucleus
• No membraneous organelles
• Do have flagella, cell wall, DNA, and ribosomes

Membraneous bound organelles
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Compartmentalization
Eukaryotic cells are full of membrane-enclosed
compartments (organelles) These separate
incompatible chemical and physical
conditions Organelles also increase surface area
for these reactions to occur.
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Examples

• The stomach in the human body separates the HCl
  from other organs. What would happen if stomach
  acid was not contained in the stomach?
• The lysosome in the cell also contains enzymes
  that break down molecules. What would happen if
  these were not contained in the lysosome?

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Cell Organelles

• Ribosomes
• Endoplasmic reticulum
• Golgi apparatus
• Vacuoles

• Lysosomes
• Chloroplasts
• Mitochondria

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Ribosomes

• Great numbers of ribosomes are found in the cell
• Found on Rough ER and floating freely in
  cytoplasm
• Make proteins as directed by the nucleus

• Ribosomes have no membrane
• Found in all cells
• They are made up of ribosomal RNA (rRNA) and
  protein
• Amino acids are bonded together to form
  polypeptides and proteins

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Ribosome Image
Click here to see a quick clip of the ribosome in
action http//www.youtube.com/watch?vID7tDAr39Ow
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Endoplasmic Reticulum

• Highly folded membrane that acts as a workspace
  (folding increases the surface area)
• There are two types of ER, rough and smooth.
• Rough ER has ribosomes attached to it, and smooth
  ER does not.

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• Smooth ER Lipid synthesis
• Rough ER Along with ribosomes involved in
  protein assembly transport within the cell
• Transports things between nucleus and cytoplasm

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Golgi Apparatus

• Made up of flattened sacs call cisternae
• This organelle modifies molecules and packages
  them into small membrane bound sacs called
  vesicles
• These sacs can be targetted at various locations
  in the cell and even to its exterior
• Produces lysosomes

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Lysosomes

• Membrane organelles that contain hydrolytic
  (digestive) enzymes and are important in
  intracellular digestion
• Digest food or old and unwanted organelles
• Also involved in apoptosis (programmed cell death)

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Vacuoles
Fat cells with large vacuole storing lipids

• Temporary storage of materials
• Involved in intracellular digestion can fuse
  with lysosomes
• Plant cells have large one and animal cells have
  many smaller ones
• Can store food, water, waste products, and
  enzymes

Plant cell with large central vacuole
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Mitochondria

• Mitochondria convert food into energy (ATP)
• The major energy production center in eukaryotes
  
• Mitochondria have a double membranes, an inner
  and an outer
• The outer membrane is smooth and the inner is
  highly folded to produce many folds called
  cristae
• Cristae increase surface area for ATP production
  and the enzymes that are responsible for it

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A sperm cell containing many mitochondria near
the tail
Figure 3-9 Mitochondria
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Chloroplasts

• These organelles are the site of photosynthesis
  in plants and other photosythesizing
  organismslike algae Capture and convert it to
  food.
• Chlorophyll is the pigment stored in chloroplasts
  that capture the energy in sunlight to convert to
  ATP. Chlorophyll a is the most important pigment
  in plants and give them their green color.
• They also have a

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Chloroplasts also have a double outer membrane
and membrane structure inside called
thylakoids. Inside the thylakoids they are
further organized into stacks called grana. This
is where the energy in sunlight is converted to
energy rich molecules like ATP and NADPH2 Carbon
fixation occurs in the stroma which is the liquid
that surrounds the thylakoids. This is where
carbon fixation takes place. In carbon fixation
CO2 is made into sugars.