Chapter 4 Cell Structure and Function

Section 1: The History of Cell Biology All living things are made up of one or more cells A cell is the smallest unit that can carry on all the processes of life

The Discovery of Cells Robert Hooke Used light microscopy to observe cork and other plant material He was observing the remains of cork cells and made some of the first sketches of cells, what he called “little boxes”

The Discovery of Cells Anton van Leeuwenhoek First person to observe living cells Made microscopes that had greater magnification than Hooke’s

The Cell Theory The importance of Hooke and Leeuwenhoek’s observation was not realized until 150 years later In the 1800’s it was determined that all plants and animals were composed of cells

The Cell Theory The cell theory has three essential parts: All organisms are composed of one or more cells Cells are the basic units of structure and function in an organism Cells come only from the reproduction of existing cells

Section 2: Introduction to Cells Cell Diversity Cells of different organisms and even cells within the same organism are very diverse in terms of shape, size, and internal organization

Introduction to Cells Cell Shape Cell shape reflects different cell functions Each cell has evolved a shape that allows it to function effectively

Introduction to Cells Cell Size The size of a cell is limited by the relationship of the cell’s outer surface area to its volume, or surface area-to-volume ratio As a cell grows its volume grows much faster than its surface area Materials must pass through the membrane (nutrients, wastes etc.) If the cells were to become too large the volume would be much larger than the S.A. and materials entering and leaving the cell wouldn’t meet the cells needs quick enough

Surface Area to Volume Ratio

Surface Area to Volume Ratio

Basic Parts of the Cell Three basic features are characteristic of all cell types Plasma membrane: the cell’s outer boundary Cytoplasm: the region of the cell that is within the plasma membrane that includes the fluid, cytoskeleton, organelles, and nucleus Control Center: Cells carry information in the form of DNA; some cells its free floating, others have it located in a nucleus

Two Basic Types of Cells Two major types of cells: Prokaryotes Eukaryotes Prokaryotes: organisms that lack a membrane bound nucleus and membrane bound organelles Eukaryotes: organisms made up of one or more cells that have a nucleus and membrane bound organelles

Prokaryotes and Eukaryotes

Comparing the Two

Two basic Types of Cells Prokaryotes Lack nucleus, but DNA is concentrated in a part of the cell called the nucleoid Broken into two main domains Bacteria Similar to first cellular life forms Archaea Organisms that are more closely related to eukaryotes

Two Basic Types of Cells Eukaryotes Contain variety of substructures called organelles—well defined, intracellular bodies that perform specific functions in the cell Organelles are like the organs in a human Generally much larger than prokaryotic cells

Cellular Organization Over time, cells began to form groups that functioned together Colonial organism: collection of genetically identical cells that live together in a connected group Not truly multicellular

Cellular Organization True Multicellularity Cells became more specialized and were unable to survive independently Tissue: group of similar cells that carry out a specific function Organs: groups of tissues that perform a particular job in an organism Organ system: group of organs that accomplish related tasks A collection of organ systems combine to form an organism

Organization

Organization

Section 3: Cell Organelles and Features Plasma Membrane aka the cell membrane Semi permeable: only lets in certain things Separates internal metabolic functions from the outside environment Allows cell to excrete wastes and interact with the outside environment

Cell Organelles and Features Membrane Lipids Made primarily of phospholipids Polar and non-polar ends Two layers: bi-layer Sterols: make membrane more firm and prevent freezing Ex: Cholesterol

Cell Organelles and Features Membrane Proteins Integral proteins: embedded within the lipid bilayer, only on one side Receptor/Transport proteins: exposed on both sides of the cell; able to detect environmental signals Peripheral proteins: lie on only on one side, not embedded

Cell Membrane

Cell Organelles and Features Fluid Mosaic Model Scientists describe the cell membrane as a fluid mosaic Fluid mosaic model states that the phospholipid bilayer behaves like a fluid more than it behaves like a solid Lipids and proteins can move within the membrane like a “boat in an ocean”

Cell Organelles and Features Nucleus Control center of the cell Filled with nucleoplasm Houses and protects genetic information DNA in chromatin form; condensed it forms chromosomes DNA is read to form RNA where it carries out functions in the cell

Cell Organelles and Features Nucleus Surrounded by the nuclear envelope, which is made up of two phospholipid bilayers Nuclear Pores: tiny protein-lined holes in the nuclear envelope that provide passageways for RNA and other materials to enter and leave the nucleus

Cell Organelles and Features Nucleus Nucleolus: a dense area of concentrated DNA within the nucleus The site where DNA produces ribosomal RNA Ribosomes: organelles made of protein and RNA that direct protein synthesis in the cytoplasm

Cell Organelles and Features Mitochondria Organelles that transfer energy from organic molecules to ATP Powerhouse of the cell Highly active cells = lots of mitochondria; less active cells = less mitochondria

Cell Organelles and Features Mitochondria Have an inner and outer cell membrane Outer: separates mitochondrion from cytosol Inner: many folds, called cristae, which contain proteins that carry out energy harvesting chemical reactions Large surface area Think! Why would mitochondria need a large surface area Has its own DNA

Cell Organelles and Features Ribosomes Responsible for building proteins Made of protein and RNA molecules Contain a large and small subunit Some are free within the cytosol, some are studded on the rough endoplasmic reticulum

Cell Organelles and Features Endoplasmic Reticulum (ER) Intracellular Highway: particles move from one part of the cell to another Two types of ER: Rough ER: covered in ribosomes, produces phospholipids and proteins Smooth ER: lacks ribosomes, builds lipids such as cholesterol Abundant in liver and kidney cells where it helps detox drugs and poisons

Cell Organelles and Features

Cell Organelles and Features Golgi Apparatus UPS factory of the cell Get vesicles (transport sacs) from the ER containing proteins or lipids, these get transported throughout the cell

Cell Organelles and Features Vesicles Small sacs that are classified by their contents Lysosomes: contain digestive enzymes that break down large molecules; involved in cell death; From golgi apparatus Peroxisomes: not from GA; break down fats

Cell Organelles and Features Cytoskeleton Thin tubes and filaments in the cytosol that give the cell its structure and shape Tent poles in a tent

Cell Organelles and Features Cilia and Flagella Hair-like structures that extend from cell’s surface; assist with movement Cilia: short; Flagella: long and less numerous Centrioles Two short cylinders of microtubules; in cytoplasm near nucleus Animal cells only Involved in cell division

Unique Features of Plant Cells Plant cells have three structures animal cells do not Cell wall Large central vacuole Plastids

Unique Features of Plant Cells Cell Wall Rigid layer that lies outside of the cell’s plasma membrane Made of cellulose Provides structure and support

Unique Features of Plant Cells Central Vacuole Reservoir that stores large amounts of water Also stores enzymes, metabolic wastes, other materials Fusion of smaller vacuoles Make up to 90% of the plant cell’s volume

Unique Features of Plant Cells Plastids Like mitochondria, contain their own DNA Chloroplasts: Use light energy to make carbohydrates from CO2 and water Contain thylakoids (pancake stacks) that contain chlorophyll, main molecule in converting light to energy Endosymbiosis: chloroplasts and mitochondria were free living prokaryotic cells that were incorporated into larger cells

Unique Features of Plant Cells