Cell Structure and Function

• Cells are the basic unit of life

Learning Strands for Unit 2

• Appreciate the development of cell theory
• Types of microscopes, microscope parts and functions
• Cell structures and functions
• Differences between prokaryotic and eukaryotic cells
• Cell specialization for obtaining nutrients through photosynthesis
• Harnessing energy in nutrients through cellular respiration
• Sexual and asexual reproduction
• Differences between unicellular and multicellular organisms

Cell Theory

• All living things are composed of one or more cells
• Cells are the building blocks and fundamental unit of life
• Cells come from the division of pre-existing cells
• Cells come in many shapes and sizes
• Most cells are microscopic
• Most cells are around 0.001 cm (1/100 of a mm or 10 µm)
• Humans are composed of about 50-100 trillion cells

Microscopes

• The study of cells is made possible by microscopy
• Cytology is the study of cell structures
• Histology is the study of tissues
• Study of the function of the cell consists of cell physiology, biochemistry, and cytogenetics
• The first microscope was used by Antoine Van Leeuwenhoek to look at animals in water in the 17th century

Types of microscopes

• Compound light microscope has a maximum revolving power of 200nm
  • Maximum magnification around 1000x
  • Uses light rays to view specimens
  • Resolving power is the ability to distinguish between 2 adjacent points
• Transmission Electron Microscope (TEM) has maximum resolving power of 0.5nm
  • Maximum magnification around 30,000X
  • Uses electrons to view preserved tissue
  • Used to view the internal details of the cells
• Scanning Electron Microscope gives vivid 3D images
  • Has less magnification than transmission EM

Cell Structures

Cell membrane

• Cell membrane also known as plasma membrane
  • A flexible boundary that controls the movement of substances into and out of the cell

Cytoplasm

• Cytoplasm is the environment inside the plasma membrane
  • Made up of semifluid material
  • All of the chemical processes in the cell occur in the cytoplasm

Cytoskeleton

• Is a supporting network of long, thin protein fibers (microfilaments)
  • Forms a framework for the cell
  • Provides an anchor for the organelles in the cells
• Helps with cell movement and other cellular activities

Nucleus

• Found in Eukaryotic cells
  • Directs the processes in the cell such as managing structure
  • Contains most of the cell's DNA (chromatin)
  • Stores information to make proteins, responsible for cell growth, function, and reproduction
  • Nuclear envelope is a double membrane that encloses the nucleus
  • Nucleolus in the nucleus is responsible for making some ribosomes
• Ribosomes are used to make proteins
  • Proteins are used by the cell or by other cells
  • Attached to rough endoplasmic reticulum or float freely

Endoplasmic Reticulum

• A highly folded membrane that is the site of protein synthesis
• Rough endoplasmic reticulum has ribosomes attached to it
• Smooth endoplasmic reticulum does NOT have any ribosomes attached to it
• Some ERs are responsible for the production of specific molecules such as hormones
  • Hormones are sent out in vesicles to the Golgi bodies when produced
  • Golgi bodies process the hormones before they are sent out of the cells by secretory vesicles in exocytosis

Golgi Apparatus

• A flattened stack of tubular membranes
  • Modifies proteins
  • Packages them for distribution outside the cell

Vacuoles

• A membrane bound vesicle for the temporary storage of materials
• Animal cells have a few smaller vacuoles
• Plant cells have a large one called a central vacuole

Lysosomes

• A vesicle that contains digestive enzymes, called hydrolytic enzymes
• Used for the breakdown of excess or worn-out cellular substances

Centrioles

• Organelles that occur in pairs are important for cell division
  • Only found in animal cells

Mitochondria

• A membrane bound organelle that makes energy available to the rest of the cell

Chloroplast

• A double membrane bound organelle that contains chlorophyll
  • Photosynthesis occurs in the chloroplast
  • Only found in plant cells

Cell wall

• An inflexible barrier that provides support and protects the plant cell

Cilia and flagella

• Projections that aid in locomotion and feeding

Prokaryotic vs Eukaryotic Cells

Prokaryotic

• Bacteria and archaea cells
  • Lack nucleus
  • Lack membrane bound organelles
  • Metabolic functions occur in the cytoplasm
  • Very tiny, around a micrometer

Eukaryotic

• Cells from Animals, plants, fungi and protists
  • Have a true nucleus and membrane bound organelles
  • More efficient, diverse and specialized than prokaryotic cells
  • 100 times larger than prokaryotic cells

How Cells Obtain Nutrients

Autotrophs

• Produce their own nutrients using energy in the environment (Sun light)
  • Plants produce glucose

Heterotrophs

• Rely on ingesting or absorbing nutrients
  • Examples are fungi and animals
• Nutrients come in by endocytosis
  • Food particles become surrounded by cell membrane to form food vacuoles
  • Later, food vacuoles merge with lysosomes that have digestive enzymes
  • Nutrients are kept and used in the cell once the food has been broken down

Photosynthetic Autotrophs

• Use sunlight and photosynthesis to produce sugar
  • Contain chlorophyll in organelles called chloroplast
  • Many types of chlorophyll exist, plants use the ones that are useful to them
• During photosynthesis energy is absorbed by the chlorophyll
  • Glucose molecules are built using carbon dioxide and water
• Chemosynthetic autotrophs do not rely on sunlight and live in harsh environments
  • Harness energy from sulfur-containing molecules

Cellular Respiration

• Once cells have nutrients they break them down to access the stored energy
• Cellular respiration occurs in the mitochondria, producing ATP (adenosine triphosphate)
  • When ATP is broken down, energy is available for the cell
• During glycolysis, glucose is broken down into a 2-carbon molecule
  • Enters the mitochondria, metabolized by enzyme complexes to produce ATP
• Some Prokaryotic cells do not have mitochondria and function anaerobically
  • Obligate aerobes need oxygen
  • Obligate anaerobes can not live in the presence of oxygen
  • Facultative anaerobes can live in the presence or absence of oxygen

Sexual vs Asexual Reproduction

• Replace dead or damaged cells
  • To grow
  • Involves Mitosis and Meiosis

Sexual Reproduction

• Involves the mixing of genes from two organisms
  • Takes longer, produces fewer offspring
  • New cells are genetically different
  • Called Conjugation in unicellular organisms
  • Produces variants in structure, ability or appearance which can help survival
  • Meiosis is required
  • At the end of meiosis each gamete (sperm and egg) has half the chromosomes (haploid)
  • Gametes fuse and produce different zygotes during fertilization
  • High chances of mutations during replication leads to genetic variation

Asexual Reproduction

• Also known as binary fission
  • Chromosomes replicate, cell divides into two identical daughter cells
  • No contribution of genetic material
  • Unicellular organisms go through binary fission if conditions are favorable
  • Allows quick mass production

Unicellular vs Multicellular Organisms

Unicellular

• Prokaryotic; bacteria and archaea bacteria
  • Simple organisms that are not compartmentalized
  • No membrane bound organelles and do not have a nucleus
  • Examples include: All Bacteria, All Protists, Some Algae, and Unicellular Fungi
    • Eukaryotic protists, such as paramecia, amoeba and euglena, are more elaborate, have a nucleus, and membrane bound organelles

Multicellular

• Made up of millions of eukaryotic cells
  • Contains organelles and a nucleus
  • Cells organized into tissue, organs and organ systems
  • Can grow very large and complex
  • Have sophisticated adaptations and abilities

Endosymbiotic Theory

• Organisms started living within another organism, eventually became an effective team that could not be separated

Explore cell theory, microscopy techniques, and cellular components. This quiz covers cell size, resolving power, and the functions of organelles like the nucleus, cytoplasm, and cytoskeleton. Test your knowledge of cell biology.