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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