Cell and Cell Membrane Structure and Function, Summaries of Construction

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Cell and Cell

Membrane

Structure

and Function

Lesson 3

The Cell Theory

• Three principles comprise the cell theory
  1. Every living organism is made up of one or more cells
  2. The smallest living organisms are single cells
  3. All cells come from preexisting cells

Basic Attributes of Cells

• All Cells Share Common Features  All cells have a plasma membrane which encloses the cell and allows interactions between the cell and its environment - The plasma membrane has three functions 1) Isolates the cell’s internal contents from the external environment 2) Regulates the flow of materials into and out of the cell 3) Allows communication with other cells

Basic Attributes of Cells

• All Cells Share Common Features  All cells contain cytoplasm - The cytoplasm consists of all the material and structures that lie inside the plasma membrane  All cells use DNA as a hereditary blueprint and RNA to copy the blueprint and guide construction of cell parts - During cell division, parent cells pass exact copies of their DNA to daughter cells

• Eukaryotic cells contain organelles  Organelles: membrane-enclosed structures that perform specific functions in the cell - The cytoskeleton is a network of protein fibers that gives shape and organization to the cell  Eukaryotic cells are not all alike - Plant and animal cells each have unique organelles that are not found in the other  Chloroplasts, plastids, and a central vacuole are found in plant cells and not in animal cells  Cilia are found in animal cells and not in plant cells

• Some eukaryotic cells are supported by cell walls  The outer surfaces of plants, fungi, and some protists are covered with cell walls - Cell walls are composed of cellulose and other polysaccharides and are produced by the cells they surround - Cell walls support and protect otherwise fragile cells but allow flow of materials  Animals cells do not have a cell wall

Cilia

• Very abundant
• Short projections located on the surface of some cells
• Provide a force parallel to the plasma membrane of the cell

Flagella

• Fewer in number than cilia
• Longer than cilia
• Provide a force perpendicular to the plasma membrane Cilia and flagella move the cell through fluid or move fluid past the cell Cilia and flagella are slender extensions of the plasma membrane

• The nucleus, containing DNA, is the control center of

the eukaryotic cell

 The nuclear envelope allows selective exchange of materials

• It is a double membrane, studded on the cytoplasm side with ribosomes
• It is perforated with pores that permit easy passage of small molecules and regulate passage of larger molecules such as RNA and protein

• The nucleus, containing DNA, is the control center of

the eukaryotic cell

 The nucleolus is the site of ribosome assembly

• It appears as one (or more) darkly staining regions in the nucleus
• Ribosomes are small, dense particles, composed of protein and RNA, that function in protein synthesis

• Eukaryotic cytoplasm contains membranes that form the endomembrane system  Eukaryotic cells have an elaborate system of membranes that are fundamentally similar in composition  Pieces of the cell membrane system can exchange membrane material with one another  The plasma membrane both isolates the cell and allows selective interactions between the cell and its environment  The cell’s membrane system includes the plasma membrane, nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, vesicles, and vacuoles

• Eukaryotic cytoplasm contains membranes that form the endomembrane system  The Golgi apparatus modifies, sorts, and packages important molecules - The Golgi resembles flattened sacs and is derived from the ER - Modifies some molecules by adding carbohydrates to some proteins to make glycoprotein - Separates proteins and lipids received from the ER according to their destination - Packages materials into vesicles and sends them to other parts of the cell or the plasma membrane for export

• Eukaryotic cytoplasm contains membranes that form the endomembrane system  Secreted proteins are modified as they move through the cell - Molecules destined for export synthesized on the rough ER are modified in the Golgi, and packaged into vesicles that fuse with the plasma membrane where the contents of the vesicle are released  Lysosomes serve as the cell’s digestive system - Membrane-bound vesicles that contain enzymes break down molecules, cell debris, foreign particles, and defective organelles - Recognize food vacuoles that result from endocytosis  Membrane is exchanged throughout the cell

• Mitochondria extract energy from food molecules, and

chloroplasts capture solar energy

 The endosymbiont hypothesis of mitochondrial and chloroplast evolution states that both mitochondria and chloroplasts evolved from prokaryotic bacteria. Similarities between mitochondria and chloroplasts include:

• Similar in size: 1–5 micrometers
• Both are surrounded by a double membrane
• Both make ATP
• Both have their own DNA and ribosomes

Mitochondria

• Mitochondria use energy stored in food molecules to produce ATP  Found in all organisms, including plants, but not bacteria  Enable cells to carry out metabolic processes to break down food molecules and generate ATP  Surrounded by a double membrane with highly folded inner membrane (folds are called cristae)  Internal fluid part of a mitochondria is the matrix

Chloroplasts

• Chloroplasts are the sites of photosynthesis  All eukaryotic life is dependent on photosynthesis  Chloroplasts are surrounded by a double membrane with internal stacks of hollow membranous sacs (thylakoids) arranged in stacks (grana)  Thylakoid membranes contain chlorophyll, a green pigment molecule that captures light  Fluid portion of chloroplast is the stroma