Cell Structure and Function

• What do all eukaryotic cells have?

  - genetic material enclosed in a nucleus

  - cell membrane composed of a phospholipid bilayer and embedded proteins

  - cytoplasm

  
• What are the differences between plant and animal cells?

  - plants have cell walls

  - animal cells tend to be circular

  - animal cells have cytoskeletons

  
• Nucleus

  - control center of the cell

  - stores and replicates DNA (genetic material)

  - each DNA in the nucleus combines with an equal mass of protein to wind up to form a chromosome

  
• What are the structures of the nucleus?

  - nuclear envelope

  - nucleoplasm

  - nucleolus

  - nucleopores

  - nuclear matrix

  
• What is nucleoplasm?

  a fluid in the nucleus

  
• What is the nuclear matrix?

  network of protein fibers providing internal structure and support

  
• What is the nucleolus?

  a denser region in the nucleus that makes ribosomes and contains DNA, proteins and chromatin

  
• What is the nuclear envelope?

  a double membrane surrounding the nucleus that consists of 2 layers of phospholipid bilayers, separating the nucleus from the rest of the cell

  
• What are nucleopores?


  groups of protein that form openings in the nuclear envelope, which allow small particles (water, ions) to flow freely through the pores but control the passage of macromolecules (e.g. RNA)

  
• Endoplasmic Reticulum (ER)


  - made up of 2 parts (rough and smooth ER)

  - complex channels and systems composed of membranes enclosing a lumen

  
• Ribosomes

  a structure composed of RNA and proteins which synthesizes polypeptides in the cytosol on the surface of the rough ER

  
• Difference between smooth ER and rough ER

  - rough ER has ribosomes and synthesizes polypeptides

  - smooth ER has no ribosomes and synthesizes lipids/lipid-containing molecules

  
• What is the function of the smooth ER?

  - synthesizes lipids and lipid-containing molecules

  - detoxifies drugs and alcohol (liver)

  - produces testosterone and estrogen (testes and ovaries)

  
• Endomembrane system


  a group of organelles between the nucleus and the plasma membrane that synthesize, modify, and transport lipids, enzymes, and proteins to other cellular destinations

  
• How are proteins transported in the cell?

  rough ER containing ribosomes produce (bud off) vesicles containing proteins which travel to the Golgi Apparatus and combine with it to release the protein

  
• How are proteins modified in the cell?

  - some polypeptide chains enter the rough ER which modify them into their final form

  - while some proteins in the vesicles get modified in the Golgi Apparatus and get transported to the rest of the cell

  
• Lysosomes


  - organelles that contain digestive enzymes that accelerate hydrolysis reactions

  - decompose old or useless parts of the cell and fight alien substances

  - works best in pH of 5, even if enzyme spills, it does not break down the cell

  
• Peroxisomes

  - organelles that form in the ER and contain enzymes that accelerate redox reactions

  - decompose biological or toxic molecules

  - the decomposition usually results in Hydrogen Peroxide, which catalase breaks down into oxygen and water

  
• Vesicles

  a sac found in many animal cells that is enclosed by a thin membrane which is formed by pinching off from the cell or organelle membranes

  
• What are the functions of vesicles?

  storage, transport, and digestion of waste products
• Vacuole

  a central vesicle in a plant cell that determines turgor pressure

  
• What are the functions of the vacuole?


  storage of water, ions, sugars, macromolecules, and amino acids
• What is turgor pressure?

  the water pressure inside the vacuole of the plant cell in response to the force of water within the cell which allows the cell to be rigid

  
• What happens if there is not enough water in a plant cell?

  the vacuole shrinks and the plant wilts, which is a decrease in turgor pressure
• what are semi-autonomous organelles?

  mitochondria and chloroplasts

  
• Mitochondria


  organelle that takes in and breaks down cell nutrients and converts it into energy (ATP) for the cell to carry out functions (also has it's own DNA that is identical to the individual's mother's mitochondrial DNA)

  
• Chloroplast


  organelle found in plants to convert sunlight into sugars that can be used by cells

  
• What is the process of photosynthesis?

  plants produce sugars and oxygen with the help of chloroplasts, which the mitochondria use to release chemical energy, carbon dioxide, and water

  
• Cell wall

  a rigid layer made out of cellulose and some proteins surrounding plant, fungal, algae, bacterial, and some archaea cells

  
• What is the cell wall's function?

  to provide cell structure and protection
• Cytoskeleton


  protein fibres extending throughout the cytoplasm that provide structure and shape for the cell

  
• Three main parts of the cytoskeleton

  microtubules, microfilaments, intermediate filaments

  
• Microtubules


  proteins that form hollow tubes (25nm in diameter)

  
• What are the functions of microtubules?

  - maintain cell shape

  - assist in cell division (spindle formation)

  - facilitate movement of organelles
• Intermediate filaments

  proteins coiled together into cables (10nm in diameter)

  
• What are the functions of intermediate filaments?

  - maintain cell shape

  - anchor organelles

  - form internal scaffolding of the nucleus
• Microfilaments


  two strands of actin wrapped together (8nm in diameter)

  
• What are the functions of microfilaments?

  - maintain cell shape

  - involved in muscle contraction (using actin and myosin)

  - assist in cell division (cleavage furrow)
• Cilia and flagella


  structures that allow a cell to move by moving water around it

  
• What are cilia and flagella made of?

  microtubules, dynein (motor protein), and covered in an extension of the plasma membrane