Review of the Cell and Its Organelles

"Organelles" is the general name for the various structures inside the cytoplasm.  Each organelle has a specific function.

 

Organelles found in both animal and plant cells: 

Cell Membrane

Cell membrane (or plasma membrane)– a layer surrounding the cytoplasm of the cell

• The function or job of cell membrane is to control what goes in and out of the cell and hold all of the cell’s contents together.
• porous membrane made up of a double layer of phospholipids (phospholipid bilayer)
• The cell membrane is semipermeable -- allows passage of nonpolar and small uncharged polar molecules though via diffusion while larger polar molecules and ions are only able to enter the cell through specialized pores.  
• This helps the membrane control what can or cannot cross into and out of the cell.

Cytosol

Cytosol -  liquid inside the cell

• everything inside the cell that isn't an organelle or protein in cytosol.  

Cytoplasm

Cytoplasm - the jelly-like substance that fills the cell

• holds the organelles in place
• Everything in the cell that isn't the nucleus - both organelles and the cytosol make up the cytoplasm.  
• It also provides a medium for the transport of materials within the cell. 

Nucleus

Nucleus - the control center of the cell

• It contains most of the genetic information (DNA) and controls all the activities of the cell.
• By using the genetic information, proteins can be produced and control the cell functioning.  
• almost always near the center of the cell

Chromatids

Chromatids - long sequences of genetic information in the form of DNA

• Only visible as the cell prepares to divide and coil to form chromosomes

Nucleolus

Nucleolus - dark area in the center of the nucleus

• Makes ribosomes

Endoplasmic Reticulum

Endoplasmic reticulum - a network that modifies and transport proteins

• Divided into two parts: the smooth endoplasmic reticulum (smooth ER) and the rough endoplasmic reticulum (rough ER)
  • The smooth ER makes lipids, such as hormones
  • Ribosomes attached to the Rough endoplasmic reticulum make proteins.
• The ER makes proteins and other molecules are then modified and moved to areas of the cell where they are needed.

Ribosomes

Ribosomes - organelles that make proteins from amino acids

• Connect molecules together into proteins.
• They can be free floating in the cytoplasm, or attached to the endoplasmic reticulum
• Made of two subunits: large and small

Golgi Apparatus

Golgi apparatus - modifies proteins by adding signaling sugars onto the surface of the proteins (post-transitional modification)

• Usually found next to the ER
• It receives the proteins from the rough ER, may make additional modifications, puts "shipping addresses" on the proteins, packages them, and then sends them to the right place in or out of the cell.

Vesicle

Transport Vesicle - carry proteins to the Golgi apparatus from the ER

• Fuses with the membrane of the Golgi and release the unmodified protein
• Once the protein is modified, the Golgi pinches off part of its membrane to form a vesicle for transportation inside or outside the cell (Exocytosis)

Mitochondria

Mitochondria – the powerhouse of the cell

• Uses chemical energy from sugars, proteins, and fats to make energy for the cell to do its metabolic tasks
• It does this by breaking apart food molecules and releasing the energy stored in them.
• The main molecule that provides chemical energy is adenosine tri-phosphate (ATP)

Peroxisomes

Peroxisomes - vesicles that contain oxidative enzymes which break down fatty acids, some amino acids, and toxic hydrogen peroxide

• Found near mitochondria and chloroplasts

Cytoskeleton

Cytoskeleton - gives cell shape, holds organelles in place and lets parts of the cell to move

• Composed of microfilaments, intermediate filaments, and microtubules

Microfilaments

Microfilaments - (actin filaments) allow the contraction and expansion of the cell and allows the cell to move in space

• Smallest and thinnest components of the cytoskeleton

Intermediate filaments

Intermediate filaments - holds the organelles in place within the cytosol and anchor the nucleus in place

• Thinner than microtubules and thicker than microfilaments 

Microtubules

Microtubules - thickest structure of the cytoskeleton

• Creates a lattice within the cell to allow organelles to move within the cell

 

 

Organelles found in many animal cells: 

Centrioles

Centrioles - organize the spindle during cell division

• Consists of 9 groups of microtubules with 3 microtubules in each group for a total of 27
• Always arranges perpendicular to each other

Lysosome

Lysosomes - (the clean-up crew) are like the garbage trucks that carry waste away from the cell.

• Inside lysosomes are hydrolytic enzymes that break down old molecules and waste products into parts that can be recycled into new ones.
• They digest invading organisms such as bacteria and also break down cells that are ready to die.
• Lysosomes are common in animal cells, but rare in plant cells.

Flagellum

Flagellum - bundle of microtubules projecting out of the cell, creating a tail-like structure

• Contracts to propel itself
• Anchored to the cell at basal bodies

Cilia

Cilia - shorter than flagellum and found in groups on the cell surface

• Can be used to move the cell or move substances across the cell surface

 

 

 

Organelles found only in plant cells:

Cell wall

Cell wall - a rigid outer barrier that supports and protects the cell.

• Attaches cells to their neighbors
• Made of cellulose which is rigid so gives plants their shape and structure
• Prevents the cell from bursting when too much water is available (water creates turgor pressure)

Chloroplast  

Chloroplasts – organelles that make food through photosynthesis

• Turn sunlight into CO² which is then used to create food (glucose) for themselves
• Because plants have chloroplasts to make their own food they do not need to obtain it from other sources.
• Give plants their green color and look like flat stacks of disks

Central Vacuole

Central Vacuoles - storage centers near the middle of the cell

• Many plant cells have one large vacuole that can occupy as much as 90% of the cell’s volume because they need to store water and other nutrients.
• Break down nutrients and organelles into useable energy components

 

Cell Examples