Cell Structure And Function

Cell Theory All organisms are composed of one or more cells. Cells are the basic unit of structure and function in organisms. All cells come only from other cells.

The Cell Cells are small so they can exchange materials with their surroundings.

Sizes of Living Things

Essential Tasks of Living Things Obtain food and energy Convert energy from an external source into a form that works within the cell Construct and maintain the molecules that make up cell structures Carry out chemical reactions Eliminate wastes Reproduce Keep records of how to build structures

Types of Cells Eukaryotic Prokaryotic

Eukaryotic Cells All cells are surrounded by a plasma membrane made of phospholipids and proteins. have membrane bound intracellular organelles. The most prominent organelle is the nucleus that controls the workings of the cell.

Eukaryotic Cells: Membrane

Eukaryotic: Structural Components Plasma membrane  regulates what enters and exits the cell. Inside the plasma membrane, the nucleus is surrounded by cytoplasm. Plant cells have a cell wall in addition to the plasma membrane.

Eukaryotic: Organelles Animal and plant cells have organelles. Organelles compartmentalize functions within the cell. Animal vs. Plant Cells organelles are similar to each other except that centrioles and lysosomes are present only in animal cells, and chloroplasts are present only in plant cells.

Eukaryotic: Animal Cell

Eukaryotic: Plant Cell

Cell Organelles

Nucleus Structure Chromatin: DNA and proteins Nucleolus: Chromatin and ribosomal subunits Nuclear envelope: Double membrane with pores Nucleoplasm: semifluid medium inside the nucleus.

Nucleus and the Nuclear Envelope

Ribosomes Protein synthesis occurs at tiny organelles called ribosomes. Ribosomes are composed of a large subunit and a small subunit. Ribosomes can be found alone in the cytoplasm, in groups called polyribosomes, or attached to the endoplasmic reticulum.

Ribosomes

Endomembrane System Consists of: Nuclear envelope (see nucleus slide) Endoplasmic reticulum Golgi apparatus Vesicles

Endomembrane: Endoplasmic Reticulum Endoplasmic reticulum (ER)  a system of membranous channels and sacules. Rough ER is studded with ribosomes and is the site of protein synthesis and processing. Smooth ER lacks ribosomes and is the site of synthesis of phospholipids and the packaging of proteins into vesicles, among other functions.

Endomembrane: Endoplasmic Reticulum

Endomembrane: Endoplasmic Reticulum

Endomembrane: Golgi Apparatus The Golgi apparatus consists of a stack of curved saccules. The Golgi apparatus receives protein and also lipid-filled vesicles from the ER, packages, processes, and distributes them within the cell. This organelle may also be involved in secretion.

Endomembrane: Golgi Apparatus

Endomembrane: Vesicles Lysosomes In animal cells only vesicles produced by the Golgi apparatus. Lysosomes contain hydrolytic enzymes and are involved in intracellular digestion.

Endomembrane: Vesicles

Endomembrane: Vesicles Vacuoles Larger in plant than animal cells Large membranous sacs in the cell that store substances (including water) Note: vesicles are smaller forms of vacuoles

Endomembrane: Vesicles

Endomembrane: Vesicles Peroxisomes Peroxisomes are vesicles than contain enzymes. The enzymes in these organelles use up oxygen and produce hydrogen peroxide. Peroxisomes are abundant in the liver where they produce bile salts and cholesterol and break down fats.

Endomembrane: Vesicles

Energy-Related Organelles The two energy-related organelles of eukaryotes are chloroplasts and mitochondria. Both organelles house energy in the form of ATP.

Chloroplasts In plant cells only A chloroplast is bounded by two membranes enclosing a fluid-filled stroma that contains enzymes. Membranes inside the stroma are organized into thylakoids that house chlorophyll. Chlorophyll absorbs solar energy and carbohydrates are made in the stroma.

Chloroplasts

Mitochondria Mitochondria are found in plant AND animal cells. Mitochondria are bounded by a double membrane surrounding fluid-filled matrix. The inner membranes of mitochondria are cristae. The matrix contains enzymes that break down carbohydrates and the cristae house protein complexes that produce ATP (usable form of energy in cells).

Mitochondria

The Cytoskeleton a network of filaments and tubules that extends from the nucleus to the plasma membrane. The cytoskeleton contains three types of elements responsible for cell shape, movement within the cell, and movement of the cell: Actin filaments Microtubules Intermediate filaments

Cytoskeleton: Actin Filaments occur in bundles or mesh-like networks. Actin filaments play a structural role in intestinal microvilli and also interact with motor molecules, such as myosin.

Cytoskeleton: Microtubules small hollow cylinders made of the globular protein tubulin. Microtubules help maintain the shape of the cell and act as tracks along which organelles can move.

Centrosome Assembles and co-ordinates the activity of the spindle fibres when the cell divides Made up of: Centrioles Cilia flagella

Centrosome: Centrioles Centrioles are short cylinders with a 9 + 0 pattern of microtubule triplets. 9 sets of microtubule triplets, with no microtubules in the middle Centrioles may be involved in microtubule formation and disassembly during cell division and in the organization of cilia and flagella.

Centrosome: Centrioles

Centrosome: Cilia and Flagella Cilia (small and numerous) and flagella (large and single) have a 9 + 2 pattern of microtubules and are involved in cell movement. Cilia and flagella move when the microtubule doublets slide past one another. Cilia moves in wave-like motion (e.g. in trachea) Flagella produce an undulating, whip-like motion Each cilium and flagellum has a basal body at its base.

Centrosome: Cilia and Flagella

Size Prokaryotic Cells Eukaryotic Cells Small (about the size of mitochondria) Between 1 – 10 micrometres Eukaryotic Cells Between 10 – 100 micrometres

Kingdoms Prokaryotic Kingdoms Eukaryotic Kingdoms **Bacteria Archaea Protista Fungi Animalia Plantae

Complexity Prokaryotes Lack membrane bound organelles Most bacteria have these constant features: Outer Boundary: Cell wall Plasma membrane Cytoplasm: Ribosomes (thousands) Thylakoids (Cyanobacteria) Innumerable enzymes

Complexity Eukaryotic Very complex Many membrane bound organelles, vesicle and transport systems See yesterdays note

Nucleus Prokaryotic Cells Eukaryotic Cells Nucleoid: Chromosome (single loop of DNA) Bacterial cells may have plasmids Self-replicating DNA molecules that contain genes such as antibiotic resistance Often used in genetic engineering Eukaryotic Cells DNA is contained in the membrane bound nucleus

Reproduction Prokaryotes binary fission (cells budding off) Creates clones of existing cells Some have pili that help cells attach to surfaces and exchange plasmids with other prokaryotic cells Eukaryotes Mitosis (cell division) Meiosis (formation of sex cells)

Other Important Points Prokaryotic Cells Bacteria that can carry out photosynthesis have thylakoids that develop from invaginations of cell membrane Thylakoids work same way as those in chloroplasts do Many bacteria also have cilia and flagella to help with locomotion

Prokaryotic Cells

Prokaryotic Cells

Evolution of Eukaryotic Cell Endosymbiotic hypothesis. Eukaryotes arose from a symbiotic relationship between various prokaryotes. Heterotrophic bacteria became mitochondria. Cyanobacteria became chloroplasts. Host cell was a large eukaryotic cell.

Evolution of the eukaryotic cell