NewWholeCh3- module 3

Chapter 3 - Cell Structure and Function

Prokaryotes, Eukaryotes and Their Structures, Cellular Evolution

Cellular Organization

• Cell Introduction

  • The cell is the first level of biological organization where life is found.

  • Cells can be categorized as prokaryotic (no nucleus) or eukaryotic (with nucleus).

  • Not all cells possess every structure, as many lose structures upon specialization.

  • Most cells are microscopic and cannot be seen with the naked eye.

  • Cell Theory

    • All living organisms are made of cells.

    • All cells arise from preexisting cells.

Cell Sizes

• Most cells can be seen with a light microscope.

• Measurement conversions:

  • 1 meter = 1000 mm = 1,000,000 μm

• Typical sizes:

  • Most bacteria: ~1 μm

  • Plant and animal cells: 10-100 μm

• Internal structures require an electron microscope to be clearly seen.

Why are Cells So Small?

• Cells interact with their environment to:

  • Gain materials and energy.

  • Excrete waste.

• These interactions require materials to pass across the cell's surface.

• Larger cells have less surface area relative to their internal volume, which limits efficiency.

Common Cell Features

• Shared by all cells (prokaryotic and eukaryotic):

  • Plasma membrane: Composed of phospholipids and proteins.

  • Chromosomes: Made of DNA.

  • Ribosomes: Protein synthesis.

  • Cytoplasm: The semi-fluid interior of the cell.

Prokaryotic Cells

• Prokaryotes include cells from Domains Eubacteria and Archaea.

• Characteristics:

  • Lack a nucleus; DNA in nucleoid region.

  • A single circular chromosome and possibly plasmids.

  • Small ribosomes and protective cell walls.

  • Structurally simple but metabolically diverse.

Bacterial Features

• Characteristics specific to bacteria:

  • Presence of peptidoglycan in cell walls.

  • Some bacteria have capsules or fimbriae (pili) for adhesion.

  • Flagella may be present for movement.

Domain Eukarya

• Key feature: Membrane-bound nucleus.

• Other membrane-bound organelles exist within eukaryotic cells, which allow for cellular specialization.

• Eukaryotic organelles can be grouped by their function:

  • Manufacturing: Nucleus, ribosomes, ER, Golgi apparatus.

  • Breakdown of molecules: Lysosomes, vacuoles, peroxisomes.

  • Energy processing: Mitochondria, chloroplasts.

  • Support and movement: Cell wall, cytoskeleton.

Animal vs. Plant Cells

• Unique to animal cells:

  • Centrioles and lysosomes.

• Unique to plant cells:

  • Cell walls, chloroplasts, and a large central vacuole.

• Other organelles are common to both types.

Organelle Group #1: Manufacturing Overview

• Nucleus: Contains instructions for protein synthesis; transcribes mRNA.

• Ribosomes: Translate mRNA into proteins.

• Rough Endoplasmic Reticulum (RER): Processes proteins; ribosomes attached for folding.

• Golgi Apparatus: Further processes and packages proteins for secretion or organelle use.

Nuclear Features

• DNA and Chromatin: DNA wrapped with proteins; condenses into chromosomes during cell division.

• Nucleolus: Dark region in the nucleus, synthesizes ribosomal RNA and assembles ribosomes.

• Surrounded by a nuclear envelope with nuclear pores for material exchange.

The Nucleus: Directing Cell Activities

• Prominent structure (~5 μm in diameter).

• All cells contain identical DNA, but different genes can be activated in various cells.

• mRNA exits the nucleus directing protein production.

Ribosomes

• Function: Build proteins based on nuclear instructions.

• Free Ribosomes: Synthesize proteins for the cytoplasm.

• Bound Ribosomes: Synthesize proteins for organelles or secretion.

• Composed of large and small subunits made of rRNA and proteins.

Endoplasmic Reticulum (ER)

• A branching network of channels and sacs extending from the nuclear envelope.

• Rough ER: Studded with ribosomes; involved in packaging and processing proteins.

• Smooth ER: Lacks ribosomes; involved in lipid synthesis, detoxification, and calcium storage.

Golgi Apparatus

• Structure: Stacked saccules (3-20).

• Functions:

  • Collects, sorts, packages, and distributes proteins and lipids.

  • Modifies products (e.g., adding carbohydrates).

  • Generates new vesicles for secretion or forming lysosomes in animal cells.

The Endomembrane System

• A series of interconnected membranes/functions within the cell:

  • Begins with nuclear envelope, connects to ER (both types), then to the Golgi apparatus.

  • Includes lysosomes and could consider the cell membrane, though it's not officially part of the endomembrane system.

Organelle Group #2: Breakdown

• Lysosomes: Digestive enzyme sacs unique to animal cells; formed from Golgi apparatus.

  • Break down particles and recycle cell components.

• Vacuoles: Large storage organelles in plants; involved in storing water, toxins, and pigments.

• Peroxisomes: Contain enzymes that break down fatty acids into hydrogen peroxide, which is then detoxified by catalase.

Organelle Group #3: Energy Processing

• Includes mitochondria and chloroplasts:

  • Mitochondria: Site of cellular respiration, converting carbohydrates and oxygen into ATP.

  • Chloroplasts: Carry out photosynthesis in plants and algae, converting light energy into carbohydrates.

• Energy and materials cycle between mitochondria and chloroplasts.

Mitochondria

• Structure: Double-membraned, containing compartments for reactions and processes.

• Function: Site of cellular respiration, involved in energy production.

Chloroplasts

• Structure: Double-membraned organelles involved in photosynthesis.

• Contains thylakoids (where chlorophyll captures light) and stroma with DNA, ribosomes, and enzymes.

Organelle Group #4: Support and Movement

• The cytoskeleton is a protein fiber network supporting the cell shape and involved in movement via motor proteins.

• Plant cells have a cell wall for additional support, which is made of cellulose.

Cytoskeleton Fibers

• Actin Filaments: Thin, flexible fibers involved in cell movement and structure.

• Intermediate Filaments: Reinforce cell shape, more permanent elements.

• Microtubules: Hollow, largest fibers involved in transporting materials and cell division.

• Centrosome: Microtubule organizing center, containing centrioles in animal cells.

Centrioles

• Cell structures in animal cells, important for cell division organization.

• Made of microtubules and replicate before cell division.

Cilia and Flagella

• Specialized structures for movement: numerous short cilia or few long flagella.

• Movement caused by the bending of microtubule pairs.

Cell Walls

• Provide support in plants and algae, composed of cellulose.

• Structural layers vary between primary (flexible) and secondary walls (rigid).

• Fungal cell walls contain cellulose and chitin.

Evolution of Eukaryotes

• Hypothesis on eukaryotic cells arising from prokaryotes.

• The Endosymbiotic Theory: Suggests that certain organelles originated from engulfed prokaryotes that were not digested.

Evidence for Endosymbiotic Theory

• Mitochondria and chloroplasts share traits with bacteria:

  • Similar size and double membranes.

  • Divide by fission; contain circular DNA.

  • Have own ribosomes resembling prokaryotic structures.

  • Genetic analysis shows similarities in RNA sequences.