A Tour of the Cell Cells and Transport

The Cell Theory All living things are made of cells. Cells are the basic unit of structure and function in living things. All cells come from other cells.

Plant and Animal Cells Each part of a cell with a specific job is called an organelle. The plasma membrane encloses the cell and regulates what comes in and out of the cell. The nucleus contains all the genetic material in the form of DNA The region inside the cell that consists of all the organelles and fluid is called the cytoplasm.

Differences of Plant and Animal Cells Plants contain chloroplasts which is the organelle where photosynthesis occurs. Only plant cells are enclosed by a strong cell wall outside the plasma membrane. The cell wall protects the plant cell and maintains its shape. Plant and animal cells are eukaryotic because the have organelles with membranes.

Prokaryotic Cells Bacteria are much simpler cells without a nucleus and organelles with membranes. Prokaryotic cells have a nucleoid that stores their genetic material (DNA) Bacteria and other prokaryotes are usually very small

Cell Membranes The cell plasma membrane separates the inside from the outside of the cell. It is responsible for regulating what comes in and out of the cell. Cell membranes are made up of a phospholipid bilayer.

Structure of the Cell Membrane The phospholipid bilayer has a hydrophobic interior and hydrophilic region facing the inside and outside of the cell. Proteins embedded in the cell membrane drift like icebergs in a sea of phospholipids. Oxygen and Carbon Dioxide (non polar) cross the membrane with ease, while sugars and ions (polar) do not.

Functions of the Cell Membrane Enzyme Activity: Enzymes embedded in the membrane catalyze reactions. Cell-to-Cell Recognition: Cells need to communicate and recognize each other to work together as an organ. Cell Signaling: Substrate signals bind and turn on messages to cells. Transport of Materials: Transport proteins move things in and out of the cell.

Regulating Movement of Molecules Materials such as water, nutrients, dissolved gasses (O2 and CO2 ), ions, and waste need to cross the cell plasma membrane. Diffusion Passive Transport Active Transport Cell Membranes are selectively permeable. This means they allow some things in and out of the cell more easily than others.

Diffusion Movement of molecules from high concentration to low concentration. Oxygen and Carbon dioxide diffuse across the membrane Dye diffuses in a glass Skunk spray spreads through the yard.

Passive Transport Passive transport is the movement of substances across a membrane without the use of energy (ATP) Facilitated Diffusion uses protein channels to allow molecules to pass through membranes.

Osmosis Osmosis is the diffusion of water (passive transport) across a membrane. Water moves from a high concentration of water to a low concentration of water Hypertonic: The concentration of solute is greater than the concentration of solute inside the cell. Hypotonic: The concentration of solute is less than the than the concentration of solute inside the cell. Isotonic: The concentration of solute inside and outside the cell is the same.

Osmosis in Plant and Animal Cells Animal cells work best in isotonic solutions. They burst (lyse) in hypotonic solutions and shrivel in hypertonic solutions Plant cells prefer hypotonic solutions. Plants need turgor pressure because they don’t have skeletons. They shrivel (plasmolysis) in hypertonic solutions and plants wilt in isotonic solutions.

Active Transport Transport that requires energy (ATP) Moves molecules the opposite direction of diffusion (against the concentration gradient).

Transport of Large Molecules If molecules are too large to fit in protein channels and pumps, they are moves in membrane vesicles. Exocytosis is the movement of molecules out of the cell Endocytosis is the movement of molecules into the cell.

Moving Things Around the Cell Each organelle has a specific job to support cell functions. Cells must obtain nutrients from outside the cell and remove waste products from the cell for disposal. The major organelles are: Nucleus Ribosomes Endoplasmic Reticulum Golgi Apparatus Vacuoles Lysosomes

Nucleus The nucleus contains all the genetic material to make every protein in your body. The nucleus is surrounded by a membrane called the nuclear envelope. The dark mass in the center makes ribosomes and is called the nucleolus.

Ribosomes Ribosomes make the proteins from the directions in the genetic material (DNA) Some ribosomes float free in the cytoplasm, while others are attached to membranes.

Endoplasmic Reticulum The endoplasmic reticulum (ER) is a huge network of membranes. The ER is responsible for the manufacturing and transport of many products of cells. The Rough ER has ribosomes attached to it that insert the proteins into the membranes stacks. These vesicles are often excreted by the cell (like saliva). The Smooth ER has no ribosomes attached. The Smooth ER makes many molecules like lipids (like hormones)

Golgi Apparatus The Golgi Apparatus modifies, stores, and transports proteins and cell products to their next location. Vesicles from the ER fuse with the receiving end and then bud off the shipping end when the Golgi processing is finished.

Vacuoles and Lysosomes Vacuoles are membrane vesicles that transport materials around the cell. Food vacuoles transport undigested nutrients. While single cellular freshwater organisms have contractile vacuoles that pump out excess water. Lysosomes fuse with food vacuoles to digest the nutrients. The also act by destroying harmful bacteria

Membrane Pathways Vesicles bud from one organelle and fuse with another, transferring membranes as well as products. As vesicles fuse, the inside side of a vesicle membrane can eventually turn up as part of the outside of the plasma membrane. As vesicles leave the cell by exocytosis, the vesicle is turned inside out.

Energy for Living Cells Cells need constant energy to support life. Two organelles support the energy process in cells: chloroplasts and mitochondria. Chloroplasts harness energy from the sun by making glucose. Mitochondria takes glucose and unpacks it into ATP. Plants have both chloroplasts and mitochondria, while animals only have mitochondria since they get glucose from their food.

Chloroplasts Chloroplasts use the sun’s energy to make glucose from CO2 and water. Chloroplasts are only in plant cells. Chloroplasts are a complex network of membranes that complete the complex reactions to join water and CO2 to make glucose.

Mitochondria The mitochondria makes adenosine triphosphate (ATP) from glucose. ATP is the energy that cells use to perform all of life’s processes. Both plants AND animals have mitochondria. Mitochondria are made up of an inner and outer membrane which increases the surface area for the chemical reactions that make ATP.

Structures to Support and Move Cells Cells need to have structures to help it move, support organelles and maintain it’s shape. These include: Cytoskeleton Flagella Cilia

Cytoskeleton The cytoskeleton is a network of fibers that support cells like a skeleton. Unlike a skeleton, cells can move by taking down cytoskeletal structures and rebuilding them elsewhere. The cytoskeleton is made of two types of filaments: Microtubules: Larger hollow tubes for structure and organization Microfilaments: Smaller solid tubes that slide past each other to contract or expand.

Structure and Function Organelles of cells must work together. Cells work together to support organs and tissues. Organs and tissues work together to support the living organism. Organisms interact and support ecosystems.