Cell Structure and Function Biology Ch. 3

3.1 Cell Theory In all branches of biology a key point to remember is that structure is related to function. Cells are the smallest units of living matter that can carry out all life processes. The invention and development of the compound microscope allowed for the discovery of cells. Compound microscopes contain 2 or more lenses. Using more lenses increases the magnification.

Robert Hooke was the first to identify and name cells. Used a compound microscope to examine thin slices of cork He observed that cork is made of tiny hollow compartments The compartments reminded him of small rooms so he named them cells. What Hooke saw was the cell walls of the cork.

Robert Hooke Microscope Drawing of a plant cell as seen by

Anton van Leeuwenhoek Used single lens microscopes that were much more powerful than Hooke’s Became one of the first people to describe living cells observing single celled organisms in pond water.

Van Leeuwenhoek microscope Microscopic life observed by van Leeuwenhoek

Matthias Schleiden Used a compound microscope to study plant tissue Proposed that plants were made of cells Theodore Schwann Observed similarities between plant and animal cells Concluded that all animals are made of cells Published the first statement of the cell theory: All living things are made of cells and cell products Rudolf Virchow Stated that all cells come from preexisting cells

The Cell Theory All organisms are made of cells All existing cells are produced by other living cells The cell is the most basic unit of life

Despite the variety of cells sizes and shapes in the body, all cells in the body share many characteristics.

Cells tend to be microscopic in size Cells have similar building blocks Cells are enclosed by a membrane that controls the movement of materials into and out of the cell. The region inside the cell membrane is filled with cytoplasm.

Cytoplasm is a jellylike substance that contains the building blocks of the cells Proteins, nucleic acids, minerals, & ions Organelles are structures that perform processes in the cell.

Cells can be separated into 2 broad categories: Prokaryotic Do not have a nucleus or membrane bound organelles DNA is suspended in the cytoplasm Most are single celled

Eukaryotic Have a nucleus and organelles The nucleus contains the DNA Can be multicellular or single celled

Additional handout Prokaryotic cells Believed to be the first cells Two major forms Archaebacteria Eubacteria Earth’s most abundant organisms Wide range of environments and obtain energy in many ways

Eukaryotic cells Larger Genetic material contained in a membrane Organelles

3.2 Cell Organelles Cytoskeleton Network of proteins that form fibers that crisscross the entire cell Microtubules: gives the cell its shape, acts as tracts for movement of organelles, and assists in cell division

Intermediate filaments: give the cell it’s strength Microfilaments: enables the cell to move and divide and play an important role in muscle contraction

Cytoplasm Fills the space between nucleus and membrane Fluid portion is called cytosol and is mostly water Location for many important chemical reactions

Nucleus Contains the DNA of the cell DNA contains the genes that have instructions for making proteins Carefully protects the DNA and ensures that DNA is available at the proper times

The membrane consists of 2 layers and is called the nuclear envelope Pores in the envelope allow larger materials to pass out of the nucleus Contains the nucleolus which is the location where ribosomes are made

Endoplasmic Reticulum (ER) Network of thin folded membranes The numerous folds allow it to fit in the cell Production of proteins and lipids Ribosomes are located on the surface of the ER Ribosomes link amino acids together to form proteins

Rough ER contains ribosomes and smooth ER does not Smooth ER makes lipids Proteins made on the ribosomes of ER are used on the cell membrane or are secreted Proteins made on suspended ribosomes are used in chemical reactions.

Golgi Apparatus Looks like layered stacks of membranes Process, sort and deliver proteins Contains enzymes that make changes to proteins Packages proteins and stores them for later use

Vesicles Small sacs that divide some materials from the rest of the cell Transports materials throughout the cell Protect proteins as they are transported to the Golgi apparatus Function in storage, transport, and secretion.

Mitochondria Supplies energy to the cell Chemical reactions that convert the food you eat into usable energy Have their own ribosomes and DNA

Vacuoles Fluid filled sac used for storage Plants contain a large central vacuole that contains a watery fluid that provides strength and support.

Lysosomes Contains enzymes Defend the cell from bacteria and viruses by engulfing them Break down worn out or damaged cell parts The enzymes form at the ER and the lysosomes form from the Golgi apparatus Contains a membrane to keep the enzymes form destroying important parts of the cell.

Centrosome and Centrioles The centrosome produces microtubules Contains 2 small centrioles Before the animal cell divides, the centrosome doubles and moves to opposite ends of the cell

Microtubules grow from each centrosome and form spindle fibers These fibers help divide the DNA during cell division Centrioles form cilia and flagella which assist in movement

Cell walls Found in plants, algae, fungi, and bacteria Rigid layer that surround the cell membrane Provides protection, support, and shape to the cell Contains channels for material to pass through

Composition varies depending on the organism: Plants and algae – cellulose Fungi – chitin Bacteria - peptidoglycan

Chloroplasts Carry out photosynthesis Contain sacs called thylakoids that contain chlorophyll Chlorophyll is the light absorbing molecule that gives plants their green color and plays a role in photosynthesis. Have their own ribosomes and DNA Plants do contain mitochondria along with chloroplasts which work together to capture and convert energy.

3.3 Cell Membrane The cell (plasma) membrane forms a boundary and controls the passage of materials. The cell membrane consists of a double layer of phospholipids A phospholipid contains 3 parts: A phosphate group Glycerol 2 fatty acid chains The glycerol and phosphate groups form the “head” of the phospholipid The fatty acids form the “tail”

The head of the phospholipid is polar The head forms hydrogen bonds with water because water is also polar The head is hydrophilic because it is attracted to water The fatty acid tails are nonpolar and are repelled by water. The tails are hydrophobic because they are repelled by water The properties of polar heads and nonpolar tails cause the structure of the phospholipid bilayer.

Structures associated with the phospholipid bilayer Cholesterol molecules provide strength Proteins allow materials to pass through the membrane Carbohydrates serve as identification tags

The fluid mosaic model is used to describe the arrangement of molecules that make up the cell membrane. The cell membrane is flexible not rigid The phospholipids move very easily The membrane behaves like a fluid Proteins stay in their positions The variety of molecules embedded in the membrane resembles a mosaic

The cell membrane is selectively permeable which means it allows some, but not all, materials to cross. The cell must be able to control the import and export of molecules and ions Different molecules pass across the cell membrane in different ways Small nonpolar molecules easily pass through the cell membrane Small polar molecules are transported by proteins Large molecules are moved by vesicles

Signal molecules allow communication with other cells A receptor is a protein found on the cell membrane that detects a signal molecule and performs an action in response. Receptors only bind to certain molecules The molecule that a receptor binds to is called a ligand There are 2 major types of receptors present in cells. Intracellular Membrane

Intracellular Found inside the cell Bind with molecules that are usually nonpolar and small such as hormones Aldosterone in the kidneys is an example which helps to regulate blood pressure.

Membrane Binds to molecules that cannot pass across the cell membrane The receptor sends the message to the cell interior causing molecules inside the cell to respond

3.4 Diffusion and Osmosis Passive transport is the movement of molecules across the cell membrane without using energy. Diffusion and osmosis are 2 types of passive transport. Diffusion is the movement of molecules in a fluid or gas from a region of high concentration to a region of low concentration. Concentration is the number of molecules of a substance

The concentration gradient is the difference in the amount of a substance from one location to another. Molecules diffuse down their concentration gradient Move from high to low concentration In cells, substances such as small lipids and nonpolar molecules such as CO2 and O2 easily diffuse across the cell membrane Diffusion occurs without the cell expelling any energy

Osmosis is the diffusion of water molecules A higher concentration of dissolved particles will lower the concentration of water molecules. A solution can be described as isotonic, hypertonic, or hypotonic.

Isotonic: solution has the same concentration of dissolved particles as the cell Water molecules move in and out at an equal rate Hypertonic: solution has a higher concentration of dissolved particles than the cell Water concentration is higher inside the cell Water flows out Hypotonic: solution has a lower concentration of dissolved particles than the cell Water concentration is higher outside the cell Water flows in

Some molecules pass through the cell membrane through transport proteins. This process is called facilitated diffusion Even though transport proteins are used, it is still a type of passive transport. Most transport proteins only allow certain ions and molecules to pass through. Some transport proteins act as simple channels while others change shape to allow molecules to pass through.

3.5 Active Transport, Endocytosis, and Exocytosis Some transport proteins in cells move materials against the concentration gradient (low to high) Transport proteins that move materials against the concentration gradient are called pumps Transport against the concentration gradient across the cell membrane is called active transport The transport proteins require chemical energy

All transport proteins span the entire cell membrane Most transport proteins change shape when they bind to a molecule just like enzymes There are different types of transport proteins: Some bind to only one type of molecule Some bind to two different types Some bind to 2 types and move them both in the same direction Some bind to 2 types and move them in opposite directions

Most transport proteins use ATP as the primary energy source In nerve cells (neurons) the sodium-potassium pump uses ATP to move sodium and potassium to opposite sides of the cell membrane during a nerve impulse conduction. The proton pump uses energy from ATP to move hydrogen ions (H+) out of the cell. This is used to power other active transport proteins.

Endocytosis is the process of taking large molecules into a cell by engulfing them in a vesicle. A lysosome breaks down the vesicle once the molecule is inside the cell allowing the molecule to be released in the cell Phagocytosis is a type of endocytosis where the cell membrane engulfs large particles. Phagocytosis is common in the immune system

Exocytosis is the release of substances out of the cell by fusion with a vesicle A vesicle forms around the material that is going to leave the cell The vesicle moves to the cell surface and fuses with the cell membrane where it releases it contents. This process occurs when a nerve impulse travels from one neuron to the next.