Cell Review
Cell Review
Prokaryotic Cells: these are simple cells that consist of little more than a cell membrane, some DNA, and cytoplasm; they do not have a nucleus or any organelles (membrane-bound structures)
Eukaryotic Cells: these are more complicated cells that contain a nucleus and organelles
Cell Structures:
Plasma membrane
• also called the cell membrane, this structure surrounds the cell to separate it from its external environment
• composed of a phospholipid bilayer that has proteins embedded in it
• cholesterol is also an important component of cell membranes since it keeps the membrane intact yet fluid
• the membrane acts as a selective barrier by allowing only certain substances to enter and leave the cell
Cell wall
• tough, rigid outer covering that protects cells and helps them maintain their shape
• found surrounding the plasma membrane of plant cells, fungi cells, most bacterial cells, and some protist cells
Nucleus
• manages all the functions of a cell
• this is where the DNA is located
• the nuclear membrane or nuclear envelope functions to separate the nucleus from the cytoplasm; it contains pores so that substances may enter or leave the nucleus
• within the nucleus is the nucleolus, a structure within the nucleus that is responsible for making ribosomes
Ribosomes
• found attached to the rough endoplasmic reticulum or suspended in the cytoplasm
• these structures use the information in a RNA strand to make proteins
Endoplasmic reticulum (ER)
• an extensive network of membranes that is
the site of many chemical reactions endoplasmic reticulum
• there are 2 types: with ribosomes
• Rough ER: contains ribosomes that make proteins
• Smooth ER: makes lipids, steroids, and is involved in detoxification; important in cells that are responsible for ridding the body of toxic substances (ex: liver)
Cytoplasm
• a semi-fluid substance in which all of the cell’s organelles are suspended
• located between the nucleus and the cell membrane
Golgi apparatus
• also called the Golgi body or the Golgi complex
• series of flat membrane-bound sacs
• packages proteins made from the RER and sends them in membrane bound vesicles to their destination
Vacuoles
• membrane-bound compartment that serves many functions (ex: absorbs water, stores proteins, stores wastes, etc.)
• plant cells have one large central vacuole whereas animal cells contain several small vacuoles
Lysosomes
• membrane-bound organelle filled with hydrolytic enzymes
• these enzymes are used to break down substances (ex: carbohydrates, proteins, lipids, old organelles, etc.)
Mitochondria
• structures that break down food molecules and transform them into energy
• has a highly-folded inner membrane surrounded by an outer membrane
• the inner membrane is where the energy-storing molecules are made
Chloroplasts
• found in plant cells and in some protists
• these structures transform light energy into chemical energy and store the energy as food
• contain chlorophyll, the green pigment that traps sunlight and gives plants their color
Cytoskeleton
• made up of tiny rods and filaments that form a framework for the cell
• provides support and helps maintain the shape of a cell as well as helping cell parts to move from place to place within the cell
Cilia
• short, hairlike extensions on the cell membrane used for movement
Flagella
• long, whip-like structures used for movement
Cell Transport:
• small molecules such as water pass freely through the membrane
• large molecules such as proteins and sugars don’t pass freely and must be transported into the cell
• although ions are small molecules, they do not pass freely through the membrane because of their charge
• passive transport:
o movement across the cell membrane without the use of energy
o includes diffusion, the movement of molecules from an area of high concentration to an area of low concentration
o ALWAYS OCCURS DOWN A CONCENTRATION GRADIENT!
o The rate of diffusion depends on temperature and the size of the molecules
• types of diffusion:
o Simple—unassisted diffusion of small particles or lipid-soluble molecules
o Osmosis—unassisted diffusion of water
o Facilitated diffusion—diffusion with the help of carrier proteins
• active transport:
o requires energy and a carrier protein
o movement from an area of low concentration to an area of high concentration
• bulk transport:
o requires energy
o there are 2 types of bulk transport:
▪ exocytosis: substances move from the cell into the extracellular space
▪ endocytosis: substances move from the extracellular space into the cell; there are 2 types of endocytosis
• phagocytosis—solid is moved into the cell
• pinocytosis—liquid is moved into the cell
Concentrations:
• isotonic
o the concentration of solutes inside the cell is equal to the concentration of solutes outside the cell
o there is no net movement of molecules in or out of the cell
o the cell maintains its normal size and shape
• hypertonic
o the concentration of solutes outside the cell is higher than inside the cell
o water moves out of the cell
o the cell shrinks
• hypotonic
o the concentration inside the cell is greater than outside the cell
o water moves into the cell causing it to swell
o if too much water enters the cell, it may burst
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