Biology Ch.4- Cell Structure and Function

Cell Theory
  • Organisms consist of one or more cells
  • Cell is the smallest unit of organization that still displays the properties of life
  • Continuity of life arises directly from the growth and division of single cells
4.1- So what is “a Cell”?
  • Cell: smallest unit with the properties of life
  • Differ in size, shape and activities

All start out with a plasma membrane, DNA (some in nucleus), and cytoplasm (basics)

Plasma Membrane
  • Thin, outer membrane which separates metabolic activities from outside events

Lets in water, carbon dioxide, and oxygen but nutrients, ions, and other substances must be escorted

Nucleus
  • Houses DNA
  • Membrane-bound
  • Occupies a nucleoid
Cytoplasm
  • Everything in between the plasma membrane and DNA

Roles in protein synthesis, energy conversions, and other vital tasks

Ribosomes

Molecular structures on which proteins are built

Cell Membranes
  • Lipid bilayer: oily boundary that prevents the free passage of water-soluble substances across it
  • Membranes in the cytoplasm form channels or sacs that compartmentalize cell tasks
  • Proteins are embedded to carry out functions
    • Channels
    • Pumps

Receptors

Surface-to-Volume Ratio
  • If a cell expands in diameter during growth, its volume will increase more rapidly than its surface area will
  • A cell that is too large will not be able to move materials into and out of the cell interior

The smaller the cell, the more efficiently materials cross its surface and become distributed through the interior

4.2- How Do We “See” Cells?

  • Research with modern microscopes supports the three generalizations of the cell theory
  • Microscopes use waves of light to make images
  • Compound light microscopes use two or more sets of glass lenses to enlarge cells up to 2,000 times

  ### More Microscopes

  • Transmission and scanning electron microscopes (TEM and SEM) use magnetic lenses to bend and diffract beams of electrons to resolve details that are 100,000 times smaller than seen with light microscopes
The Last of Microscopes

  • TEMs pass electrons through the specimen to provide images of internal details

  • SEMs direct a beam of electrons back and forth across a surface of metal-coated specimens causing electrons and x-rays to be emitted that are converted to an image of the specimen’s surface

4.3- Introducing Prokaryotic Cells 

  • Smallest known cells

  • Most metabolically diverse

  • Bacteria and Archaea

  • Lacking of a nucleus

  • Rigid cell wall to support the cell and surround the plasma membrane regulating transport into and out of the cell

  • Sticky polysaccarides help cells attach to surfaces

More Prokaryotes 

  • Bacterial flagella project from the membrane and permit rapid movement; pill filaments aid in attachment to surfaces

  • Many bacteria have plasma membrane infoldings that are photosynthetic as do the cyanobacteria

Last of the Prokaryotes

  • Ribosomes are dispersed throughout the cytoplasm

  • The bacterial chromosomes is a single, circular DNA molecule'; other smaller circles of DNA called plasmids are presents in some bacteria

4.4- Introducing Eukaryotic Cells 

  • Organelles

  • Outer membrane encloses and sustains a micro-environment for cell activities

  • Control the types and amounts of substances entering or leaving

  • Concentrate some substances for reactions and isolate or dispose of incompatible or toxic substances

  • Interact to keep a cell running

4.5- The Nucleus 

  • Holds 46 DNA molecules (2 n)-humans

  • Two main functions:

  1.) Keep the DNA from getting tangled with the cytoplasmic machinery and isolate it from potentially damaging reactions

   2.) The outer membranes are a boundary where cells control the movement of substances to and from the cytoplasm

Nuclear Envelope 

  • Double membrane

  • Outer membrane merges with the endoplasmic reticulum and has ribosomes

  • Inner membrane is bathed in a semifluid matrix called nucleoplasm and has attachments to anchor DNA and keep them organized

  • Membrane protein functions

-- Receptors or transporters

-- Form pore complexes where stuff passes

Nucleolus 

  • Where ribosomal subunits are constructed

  • Has genes which code for rRNA

Chromatin

  • Cells’ collection of DNA and all associated proteins

  • Chromosome: double-stranded DNA and protiens

4.6- The Endomembrane System 

  • Endoplasmic Reticulum

  • Polypeptide (proteins) chains are modified into final proteins

  • Lipids are assembled

  • Vesicles break off and deliver to Golgi Bodies

  • Rough ER: has ribosomes attached; where proteins are made

  • Smooth ER: makes lipids, breaks down fatty acids, degrades toxins, and functions in muscles contractions

Golgi Bodies 

  • Attach sugar side chains to proteins and lipids (reassembling)

  • Cleave some proteins

  • Package finished product in vesicles

Vesicles

  • Tiny storage sacs

  • Transport substances

  • Lysosomes: bud from Golgi bodies and participate in intracellular digestion using hydrolytic enzymes

  • Peroxisomes: hold enzymes which digest fatty acids, amino acids, and hydrogen peroxide

  • Fuse to form vacuoles

4.7 - Mitochondria

  • Specialized in ATP formation

  • Aerobic process (uses oxygen)

  • No tin prokaryotic cells but in nearly all eukaryotic cells

  • Number is based on energy needs

  • Resemble bacteria

  -- Own DNA

  -- Divide on their own

  --Some ribosomes

  • Endosymbiosis?

4.8- Specialized Plant Organelles 

  • Plastids

  • Function in photosynthesis or storage

  • Types:

  • Chloroplast: photosynthesis

  • Thylakoid: actual site of photosynthesis within chloroplasts

  • Chlorophylls: most abundant; reflect green light

  • Evolved by endosymbiosis

More Plant Organelles
  • Chromoplasts

  -- Not chlorophylls

  --Carotenoids: red or yellow color to attract pollinating animals

  • Amyloplasts

--Pigment free

--Store starch grains in stems, potato tubers, and seeds

Last of the Plant

  • Central Vacuole

  • 50-90% of cell’s interior

  • Stores amino acids, sugars, ions, and toxic wastes

  • Expands during growth and increase fluid pressure on cell wall

4.9 - Cell Surface Specialization 

  • Eukaryotic Cell Walls

  • Single-celled (protists and fungi)

  • Protects and physically supports a cell and impacts shape of it

  • Porous

  • Animal cells DO NOT have

More Eukaryotic Cell Walls

  • Primary Wall: composed of pectin, glue-like polysaccharides and cellulose to form a stiick substance cementing abutting cells together

  • Secondary Wall: reinforces cell shape

  • In woody plants, 26% made of ligin making parts waterproof, less susceptible to plant-attacking organisms and stronger

4.10 - Even Cells Have A Skeleton

  • Skeleton: anything that forms a framework

  • Cytoskeleton:

-- Organized system of protein filaments that extends between the nucleus and plasma membrane

-- Reinforce, organized, and move cell parts

Types of Cytoskeleton in Eukaryotic Cells 
  • Microtubules

  -- Largest

  -- Help keep organelles and cell structures in place or move them to new locations

  • Microfilaments

  -- Thinnest

  --Often organized in bundles or networks

  -- Anchor membranes proteins and components of muscle contraction

  • Intermediate filaments

--Between in size

--Strengthen and maintain the shape of cells and cel parts

--Used to identify cell types because cells contain one or two different kinds

-- Useful for cancer diagnosis

Prokaryotic Cell Cytoskeleton 

  • Recently identified reinforcing filaments in bacteria

  • Like tubulin and actin in pattern of assembly

4.11 - How Do Cells Move?

  • Motor proteins

  --Kinesins, dyneins, myosins, and others

  --Fueled by ATP

  -- Move chromosomes, slide, microtubules over each other, inside nerve cells

  • Cilia

  --Many hair-like structures

  --Line lungs

  • Flagella

  --Long, whip-like

  • Pseudopods

  -- “false feet”

  --Macrophanges and amoebas

  --Temporary, irregular lobes bulging out of a cell

  --Engulf prey or other target