Chapter 4 Cells, Cell Structure & Cell Transport


Download Chapter 4 Cells, Cell Structure & Cell Transport


Preview text

BIO10

ch4 Cells

13

Chapter 4 Cells, Cell Structure & Cell Transport

Cell theory 1.All organisms are composed of one or more cells
2.Cell are the smallest living things
3.Cells arise only by division of previously existing cells



13

BIO10

ch4 Cells

14

Cellular structure is organized
The Plasma Membrane • A phospholipid has a polar head and two non-polar tails
• polar region: phosphate chemical group and is water-soluble
• non-polar region: fatty acids and is water-insoluble
Interior of lipid bilayer is NONPOLAR: no water soluble molecules can cross • cholesterol is also found in the interior o affects the fluid nature of the membrane o accumulation in walls of bld vessels » plaques o plaques lead to cardiovascular disease • Plasma membrane proteins: embedded within the lipid bilayer

transmembrane proteins: form channels that span the membrane other proteins are integrated into the structure of the membrane
• Ie: cell surface proteins: attached to outer surface of the membrane/ act as markers

There are two major types of cells

prokaryotic the simplest cellular organisms lacks a nucleus/ No extensive system of internal membranes all bacteria and archaea have this cell type have a plasma membrane surrounding a cytoplasm without interior compartments some bacteria have additional outer layers to the plasma membrane

Eukaryotic Larger in size &more complex has a nucleus has internal membrane-bound compartments all organisms other than bacteria or archaea have this cell type



14

BIO10

ch4 Cells

15

cell wall comprised of carbohydrates to confer rigid structure capsule may surround the cell wall

Prokaryotic Interior: simple, uniform cytoplasm, ribosomes (protein synthesis) are scattered t/o the cytoplasm
nucleoid region (where DNA is localized)
flagellum (plural, flagellae) is a collection of protein fibers that extends from the cell surface .
• aids in attaching to substrates and in exchanging genetic information between cells
• may be one or many • aids in locomotion and feeding • pilus (plural, pili) is a short flagellum

Eukaryotic Cells larger and more complex
have a plasma membrane encasing a cytoplasm internal membranes form organelles
cytoplasm is semi-fluid & has a network of protein fibers that form a scaffold called a cytoskeleton
Nucleus: a membrane-bound compartment for DNA. The Cell’s Control Center/ stores hereditary information
endomembrane system: gives rise to internal membranes found in cell each compartment can provide specific conditions favoring a particular process



15

BIO10

ch4 Cells

16

not all eukaryotic cells are alike. • The cells of plants, fungi, and many protists have a cell wall beyond the plasma membrane • all plants and many protists contain organelles called chloroplasts • plants contain a central vacuole • only animal cells contain centrioles
NUCLEUS: • The nuclear surface is bounded by a double-membrane called the nuclear envelope
• groups of proteins form openings called nuclear pores that permit proteins and RNA to pass in and out of the nucleus
Inside the nucleus Chromosomes: Segments of DNA packaged w/ protein
• the proteins enable the DNA to be wound tightly so it appears condensed
• the condensed or chromosome form of DNA occurs during cell division
• When cell is not dividing DNA is stored as chromatin (hard to see)
• protein synthesis occurs when the DNA is in the chromatin form
What else is in the nucleus? nucleus is the site for the subunits of the ribosome to be synthesized
Nucleolus: dark-staining region of nucleus • it contains the genes that code for the rRNA (ribosomal RNA) that
makes up the ribosomal subunits • the subunits leave the nucleus via the nuclear pores and the final
ribosome is assembled in the cytoplasm



16

BIO10

ch4 Cells

17

The Endomembrane System: an extensive system of internal membranes some of the membranes form channels and interconnections other portions become isolated spaces enclosed by membranes (vesicles)
• RER: protein synthesis the surface of this region looks pebbly the rough spots are due to embedded ribosomes
• SER: carbohydrate & lipid synthesis the surface of this region looks smooth because it contains no embedded ribosomes
After synthesis in ER, the newly-made molecules are passed to Golgi bodies (flattened membranes that form collective stacks called the Golgi complex)
• their numbers vary depending on the cell • collect, package, and distribute molecules manufactured in the
cell • The ER and Golgi complex function together as a transport system in
the cell
The Golgi complex also gives rise to 1. lysosomes contain enzymes that the cell uses to break down macromolecules worn-out cell parts are broken down & recycled to form new parts particles that the cell has ingested are also digested
2. Peroxisomes the chemical reactions in peroxisomes
• 1.detoxify harmful byproducts of metabolism • convert fats to carbohydrates in plants seeds for growth

Organelles That Contain DNA: nucleus, mitochondria, chloroplasts



17

BIO10

ch4 Cells

18

The Theory of Endosymbiosis
some organelles evolved from a symbiosis in which one cell of a prokaryotic species was engulfed by and lived inside of a cell of another species of prokaryote
the engulfed species provided their hosts with advantages because of special metabolic activities
the modern organelles of mitochondria and chloroplasts are believed to be found in the eukaryotic descendants of these endosymbiotic prokaryotes

Evidence supporting endosymbiotic theory
1. Mitochondria: ~same size as modern bacteria the cristae in mitochondria resemble folded membranes in modern bacteria
2. mitochondrial ribosomes are similar to modern, bacterial ribosomes in size and structure
3. mitochondria divide by fission, just like modern bacteria



18

BIO10

ch4 Cells

19

The Cytoskeleton: Interior Framework of the Cell
• internal framework of protein fibers thatanchor organelles to fixed locations
• support the shape of the cell • helps organize ribosomes and enzymes needed for synthesis
activities • The cytoskeleton is dynamic and its components are continually
being rearranged

Three different types of protein fibers comprise the cytoskeleton 1. intermediate filaments: Thick ropes of intertwined protein
2. microtubules: hollow tubes made up of the protein tubules Microtubules provide a means to transport material inside the cell efficiently over long distances

3. microfilaments: long, slender microfilaments made up of the protein actin

Centrioles are complex structures • assemble microtubules in animal cells and the cells of most protists • anchor organelles such as flagella/cilia • assemble microtubules near nuclear envelope • they might also have an endosymbiotic origin
The cytoskeleton also anchors storage compartments • Vacuoles:membrane-bound storage centers
• central vacuole: lrg space inside a plant cell filled w/ water/dissolved substances
• contractile vacuole is found near the cell surface of some protists and accumulates excess water from inside the cell that it then pumps out



19

BIO10

ch4 Cells

20

Outside the Plasma Membrane

Cell walls • found in plants, fungi, and many protists
• comprised of different components than prokaryotic cell walls
• provides protection, maintains cell shape, prevents excessive water loss/uptake

Extracellular matrix (ECM) • comprised by a mixture of proteins secreted by cell • collagen and elastin proteins form a protective layer over the cell surface
• fibronectin protein connects the ECM to the plasma membrane ECM influences cellular behavior and coordinates groups of cells functioning as tissues



20

BIO10

ch4 Cells

21

Diffusion and Osmosis: Movement of water and nutrients into a cell or elimination of wastes out of cell is essential for survival
This movement occurs across a biological membrane in one of three ways diffusion
membrane folding
protein transport



21

BIO10

ch4 Cells

22

PASSIVE TRANSPORT across the plasma membrane.
Diffusion:
The net movement of molecules from an area of higher concentration to an area of lower concentration is termed diffusion
• Molecules diffuse down a concentration gradient from higher to lower concentrations
• diffusion ends when equilibrium is reached
• Only certain substances undergo diffusion across the plasma membrane
• Ie: oxygen, carbon dioxide, and nonpolar lipids ions and polar molecules cannot cross the interior of the membrane
• Water, although polar, is able to diffuse freely across the plasma membrane
• aquaporins are selective channels that permit water to cross

Osmosis: the diffusion of water
Water moves down its concentration gradient moving into/out of a cell the movement of water is dependent on the concentration of other substances in a solution
• the greater the amount of solutes that are dissolved in a solution, then the lesser the amount of water molecules that are free to move

• The concentration of all molecules dissolved in a solution is called the osmotic concentration of the solution

• Osmotic concentrations of different solutions can be compared relative to each other



22

Preparing to load PDF file. please wait...

0 of 0
100%
Chapter 4 Cells, Cell Structure & Cell Transport