Unit 2: The Cell

• Ribosomes translate mRNA into amino acid sequences during protein synthesis
• Amino acids with nonpolar side groups are hydrophobic. These hydrophobic amino acids associate with the hydrophobic fatty acid region of the cell membrane
• Amino acids with charged side groups are hydrophilic. These hydrophilic amino acids associate with the hydrophilic phosphate region of the cell membrane
• Saturated fatty acids have hydrocarbon tails with a straight structure. A straight structure allows many saturated fatty acids to be densely packed together, which makes the cell membrane more rigid
• Kinks form in the hydrocarbon tails of unsaturated fatty acids due to double bonds between carbon atoms. These kinks increase the spacing between cell membrane components which prevents dense packing and promotes fluidity within the cell membrane
• At high temperature, high amounts of cholesterol decrease the fluidity of the cell membrane
• Hydrophilic phosphate regions positioned towards aqueous environments
• The cell membrane becomes more rigid as the amount of saturated fatty acids with a straight structure increases
• Small nonpolar molecules are hydrophobic. Since the lipid region of the cell membrane is also nonpolar and hydrophobic, small nonpolar molecules are able to freely pass across it.
• The cell wall is a semipermeable structural boundary that allows some substances to enter the internal environment.
• The cell membrane is permeable, so it allows for the passage of substances both into and out of the cell. It is also selective, so only specific substances can enter and exit the cell.
• Ions are charged and hydrophilic, so they are transported across the cell membrane by embedded channel proteins.
• What happens to a plant cell in a hypertonic solution?


  The cell will lose water and may plasmolyze
• What happens to a red blood cell in a hypotonic solution?


  The cell will swell and may burst
• What happens to a plant cell in a hypotonic solution?


  The cell will take up water and become turgid
• What determines the direction of water movement in osmosis?


  The water potential, influenced by solute and pressure potential
• What is endocytosis?


  Taking materials into the cell
• What is exocytosis?


  Releasing materials from the cell
• What is the direction of water movement in relation to water potential?

  Water moves from areas of higher water potential to lower water potential
• How does adding solutes affect water potential?

  Adding solutes decreases water potential
• What effect does increasing pressure have on water potential?

  Increasing pressure increases water potential
• What are the effects of different types of solutions on cells?

  • Hypotonic solutions: Cell swells (may burst in extreme cases)
  • Hypertonic solutions: Cell shrinks (plasmolysis in plant cells)
  • Isotonic solutions: No net water movement
• In a hypotonic solution, what happens to the cell?

  Water moves into the cell, causing it to swell
• What occurs in a hypertonic solution?

  Water moves out of the cell, causing it to shrink
• What happens in an isotonic solution?

  No net movement of water, cell size remains unchanged
• How does water movement differ in hypotonic, hypertonic, and isotonic solutions?

  Hypotonic: water enters; Hypertonic: water exits; Isotonic: no net movement
• What is the direction of movement in passive transport?


  From an area of higher concentration to lower concentration
• Gases such as N2 O2 and CO2 are nonpolar and hydrophobic. Since the lipid regoin of the cell membrane is also nonpolar snd hydrophobic, gases are able to freely pass across it.