Post on 17-Jun-2020
Cell Structure and Function
Chapter 7Freshwater diatoms – unicellular algae with hard silica cell
wall – come in many shapes and sizes.
Lesson Overview Life Is Cellular
Chapter Mystery – Death by…Water?
• Michelle was a healthy 25-year-old running in her first marathon.
• The hot and humid weather had made all the runners sweat profusely, so Michelle made sure to drink water at every opportunity.
• Gradually, she began to feel weak and confused.
• At the end of the marathon, Michelle staggered into a medical tent.
• Complaining of a headache and nausea, she collapsed onto the floor.
• Volunteers quickly gave Michelle water for dehydration
• Soon, her condition worsened and Michelle was rushed to the hospital, where she was gripped by a seizure and went into a coma.
• Why did treating Michelle with water make her condition worse?
As you read this chapter, look for clues to help you predict how water made Michelle sick.
Life is Cellular
Section 7.1
Freshwater diatoms – unicellular algae with hard silica cell
wall – come in many shapes and sizes.
Lesson Overview Life Is Cellular
• The building blocks of living things
• Some organisms are made of 1 cell
– Unicellular (bacteria)
• Some organisms are made of many cells
– Multi-cellular (plants, animals)
Lesson Overview Life Is Cellular
Early Microscopes
• 1665 – Robert Hooke, Englishman –used microscope to observe piece of cork
coined the term cells
-Made of many tiny compartments,
like rooms in a monastery called “cells”
Lesson Overview Life Is Cellular
Early Microscopes • Anton van Leeuwenhoek: the first to
observe living microorganisms.
• using a microscope, found organisms in pond water, drinking water, and even his mouth
- The drawings on the above show
bacteria in the human mouth.
Lesson Overview Life Is Cellular
The Cell Theory
• Cells – basic unit of life• Cells are many different shapes and
sizes
• But all cells have a Cell membrane
– thin, flexible barrier that surrounds the cell
• Cell Theory:
-All living things are made up of cells.
-Cells are the basic units of structure and function in living things.
-New cells are produced from existing cells.
Lesson Overview Life Is Cellular
Light Microscopes
• Light microscopes: allow light to pass through a specimen and uses two lenses to form an image
● Light microscopes – can see cells and cell structures – use stains
○ Can be magnified up to 500x• Using chemical stains or dyes can allow us
to see structures within living cell, which are nearly transparent
- Some of these stains are so specific
that they reveal only compounds or structures within the cell.
Lesson Overview Life Is Cellular
Electron Microscopes
• Electron microscopes use beams of electrons, not light, that are focused by magnetic fields.
• Electron microscopes offer much higher resolution
than light microscopes.
• Electron microscopes (2 types)
1.Scanning electron microscope – produces dramatic 3D images
- Have 3750x magnification
2. Transmission electron microscope – samples are cut in thin slices, making a flat 2D image
- Have 4375x magnification
Lesson Overview Life Is Cellular
Electron Microscopes
• Scanning electron microscope: use a pencil-like beam of electrons that is scanned over the surface of a specimen
- specimens do not have to be cut into thin slices
- can only view nonliving cells and tissues that have been preserved
- produce 3D images of specimen’s surface
Lesson Overview Life Is Cellular
Electron Microscopes
• Transmission electron microscope: make it possible to explore cell structures and large protein molecules
- samples must be cut into ultra thin slices
- produce flat, 2D images
Lesson Overview Life Is Cellular
• Cells fall into 2 broad categories,
– based on the presence or absence of a _________
– _________ = large, membrane-enclosed structure that contains genetic material called DNA
– Prokaryotes (bacteria)
– Eukaryotes (animals, plants)
Lesson Overview Life Is Cellular
Prokaryotes and Eukaryotes
* All cells contain the molecule that carries biological information—DNA.
* All cells are surrounded by a thin, flexible barrier called a cell membrane.
Lesson Overview Life Is Cellular
Prokaryotes and Eukaryotes
* Cells fall into two broad categories, depending on whether they contain a nucleus.
* Nucleus: a large membrane-enclosed structure that
contains the cell’s genetic material in the form of DNA.
- The nucleus controls many of the cell’s activities.
Lesson Overview Life Is Cellular
Prokaryotes and Eukaryotes
Eukaryotes: cells that enclose their DNA in nuclei.
Prokaryotes: cells that do not enclose DNA in nuclei.
Lesson Overview Life Is Cellular
Prokaryotes
• Smaller
• Simple
• Grow, reproduce, and respond to environment
• Some can move by gliding along surfaces or swimming through liquids
• Example: bacteria
Lesson Overview Life Is Cellular
Eukaryotes
• Larger
• More Complex
• Highly specialized
• Contain dozen of structures and internal membranes
• Examples: plants, animals, fungi, protists
Lesson Overview Life Is Cellular
Prokaryotes
• No nucleus (DNA floats freely)
• Unicellular
• Small and simple
• Some swim or glide along surfaces
Eukaryotes
• Nucleus (contains DNA)
• Multi-cellular
• Large and complex
Lesson Overview Life Is Cellular
• No, it is not a cell, and it is not alive
• Viruses are nonliving particles
– Made of proteins, nucleic acids (DNAor RNA), and sometimes lipids (fats)
• Can ONLY reproduce by infecting living cells (remember cell theory?)
Lesson Overview Life Is Cellular
• Many shapes and sizes – All very small – need what type of microscope …?
• Viruses have a protein coat called a capsid
• Bacteriophages – virus that infects bacteria
• Once inside bacteria, it makesmany copies of itself
• Breaks open and infects other cells
Lesson Overview Life Is Cellular
Mystery Clue #1
• At the hospital, a sample of Michelle’s blood was drawn and examined.
• The red blood cells appeared swollen.
• What kind of microscope was most likely used to study the blood sample?
Cell Structure
Section 7.2
Freshwater diatoms – unicellular algae with hard silica cell
wall – come in many shapes and sizes.
Lesson Overview Life Is Cellular
Cell Organization
* Cytoplasm: fluid portion of the cell outside the nucleus, contains all the organelles of the cell
* Organelle: specialized cellular structure
Lesson Overview Life Is Cellular
Comparing the Cell to a Factory
The eukaryotic cell is much like a living version of a modern factory.
The specialized machines and assembly lines of the factory can be compared to the different organelles of the cell.
Cells, like factories, follow instructions and produce products.
Lesson Overview Life Is Cellular
The Nucleus
In the same way that the main office controls a large factory, the nucleus is the control center of the cell.
Contains:
- all the cell’s DNA
- instructions for making proteins and other molecules
Lesson Overview Life Is Cellular
The Nucleus
- Nuclear Envelope: two membrane structure that surrounds the nucleus
- Nuclear Pores: dot the nuclear envelope, allows substances to pass into and out of nucleus
- Nucleolus: small, dense region where the assembly of ribosomes begins.
Lesson Overview Life Is Cellular
The Nucleus
- Chromatin: complex of DNA bound to proteins
- chromosomes that are
spread throughout the nucleus
- chromosomes contain
the genetic information
that is passed from one
generation of cells to the next
Lesson Overview Life Is Cellular
Vacuoles and Vesicles
- Vacuoles: large, saclike, membrane-enclosed
structure that stores materials such as water, salts, proteins, and carbohydrates
Lesson Overview Life Is Cellular
Vacuoles and Vesicles
- Vesicles: small membrane-enclosed structures that
are used to store and move materials between cell organelles, as well as to and from the cell surface
Lesson Overview Life Is Cellular
Lysosomes
- Lysosomes: small organelles that are filled with enzymes that function as the cell’s clean up crew.
- breakdown lipids, carbohydrates, and
proteins into smaller molecules that can be used by the rest of the cell
Lesson Overview Life Is Cellular
The Cytoskeleton
- Cytoskeleton: help to transport
materials between different parts of
the cell, provide structural support to the cell.
- Microfilaments: threadlike
structures made up of a protein called actin
- produce a tough, flexible
framework that supports thecell
- help cells move
Actin filaments are shown
in red, microtubules in
green, and the nuclei are in
blue.
Lesson Overview Life Is Cellular
Microtubules
- Microtubules are hollow structures made up of proteins known as tubulins
- maintain cell shape
- important in cell division to separate chromosomes
- help build cilia and flagella which help in cell movement
- are arranged in a “9+2” pattern
- Centrioles: located near the nucleus and help to organize cell division (not found in plant cells)
Lesson Overview Life Is Cellular
Ribosomes
- Ribosomes: small particles of RNA and protein found throughout the cytoplasm in all cells.
- produce proteins
Lesson Overview Life Is Cellular
Endoplasmic Reticulum
- endoplasmic reticulum:
where lipid components
of the cell membrane are
assembled, along with
proteins and other
materials that are exported from the cell
Lesson Overview Life Is Cellular
Endoplasmic Reticulum
- Rough ER:
- involved in synthesis of proteins
- has ribosomes on its surface
Lesson Overview Life Is Cellular
Endoplasmic Reticulum
- Smooth ER:
- ribosomes are not found in surface
- contains enzymes that
perform specialized tasks
Lesson Overview Life Is Cellular
Golgi Apparatus
- Golgi Apparatus: proteins are bundled into vesicles that bud from the ER
- modifies, sorts and packages proteins
- ships proteins to their final destination
Lesson Overview Life Is Cellular
Chloroplasts
- Chloroplasts: capture sunlight and
convert energy into food that contains chemical energy
- Surrounded by two-membranes and contains its own DNA
- Contains large stacks of
membranes that contain the green pigment chlorophyll
Lesson Overview Life Is Cellular
Mitochondria
- Mitochondria are the power plants of the cell
- Convert the chemical energy stored in food into
compounds that are more convenient for the cell to use
- Surrounded by two-membranes and contains its own DNA
- you get nearly all your mitochondria from your mom ☺
Lesson Overview Life Is Cellular
Cellular Boundaries
- Cell wall: a strong supporting layer around the cell membrane
- Provide support and protection
- Prokaryotes, plants, algae, and fungi have cell walls
- Animal cells no not have cell walls
Cell Transport
Section 7.3
Freshwater diatoms – unicellular algae with hard silica cell
wall – come in many shapes and sizes.
Lesson Overview Life Is Cellular
Cell Membranes
- Cell membrane: regulates what enters and leaves the cell and also protects and supports the cell
- Lipid Bilayer: double-layered sheet that gives cell
membrane a flexible structure and forms a strong barrier
Lesson Overview Life Is Cellular
The Properties of Lipids
- Hydrophobic: the fatty acid portion, “water-hating”
- Hydrophilic: the opposite end of the molecule, “water-loving.”
Lesson Overview Life Is Cellular
The Properties of Lipids
The head groups of lipids in a bilayer are exposed to
water, while the fatty acid tails form an oily layer inside the membrane from which water is excluded.
Lesson Overview Life Is Cellular
The Fluid Mosaic Model
- Most cell membranes contain protein molecules that are embedded in the lipid bilayer
- Carbohydrate molecules are attached to many of these proteins.
Lesson Overview Life Is Cellular
The Fluid Mosaic Model
- Called a “fluid mosaic” because the proteins
embedded in the lipid bilayer can move around and
“float” among the lipids, and because so many
different kinds of molecules make up the cell membrane
Lesson Overview Life Is Cellular
The Fluid Mosaic Model
- Some of the proteins form channels and pumps that help to move material across the cell membrane
- Many of the carbohydrate molecules act like
chemical identification cards, allowing individual cells to identify one another
Lesson Overview Life Is Cellular
The Fluid Mosaic Model
- Permeable substances: those that can cross the cell membrane
- Impermeable substances: those that can not cross the cell membrane
- Selectively Permeable (semipermeable): some
substances can pass across membrane, other cannot
Lesson Overview Life Is Cellular
Diffusion
- Diffusion: particles move from an area of high concentration to an area of lower concentration
- Does not require energy!
Lesson Overview Life Is Cellular
Diffusion
STEPS:
1. There is a higher concentration of solute on one side of the membrane than on the other
Lesson Overview Life Is Cellular
Diffusion
2. Diffusion causes a net movement of solute particles
from the side of the membrane with the higher solute
concentration to the side with the lower solute concentration
Lesson Overview Life Is Cellular
Diffusion
3. Once equilibrium is reached, solute particles continue
to diffuse across the membrane in both directions but
at approximately equal rates, so there is no net change in solute concentration
Lesson Overview Life Is Cellular
Facilitated Diffusion
- Facilitated Diffusion: molecules that cannot directly
diffuse across the membrane pass through special protein channels
- Does not need energy!
Lesson Overview Life Is Cellular
Osmosis: An Example of Facilitated Diffusion- aquaporins: protein that allow
water to pass right through them.
- Without aquaporins, water
would diffuse in and out of cells very slowly.
The movement of water through cell
membranes by facilitated diffusion is an
extremely important biological process—the
process of osmosis.
Lesson Overview Life Is Cellular
Osmosis: An Example of Facilitated Diffusion
- Osmosis: the diffusion of water through a selectively permeable membrane.
- involves the movement of water molecules from
an area of higher concentration to an area of lower concentration.
Lesson Overview Life Is Cellular
Osmotic Pressure
For organisms to survive, they must have a way to balance the intake and loss of water.
- The net movement of water out of or into a cell exerts a force known as osmotic pressure.
Lesson Overview Life Is Cellular
Osmotic Pressure
Isotonic Solution : concentration of solutes is the same inside and outside the cell.
- Water molecules move equally in both directions
- neither gain nor loss of water
Lesson Overview Life Is Cellular
- Hypertonic Solution: the solution has a higher concentration than the cell
- A net movement of water molecules out of the cell causes the cell to shrink
Osmotic Pressure
Lesson Overview Life Is Cellular
Osmotic Pressure
- Hypotonic Solution: the solution has a lower solute concentration than the cell
- A net movement of water molecules into the cell
- Water tends to move quickly into a cell, causing it to swell
- eventually, the cell may burst
Lesson Overview Life Is Cellular
Active Transport
- Active Transport: movement
of material against a concentration difference
- Require energy
- generally carried out by
transport proteins, or
protein “pumps,” that are
found in the membrane itself
Lesson Overview Life Is Cellular
Molecular Transport
Small molecules and ions are
carried across membranes by
proteins in the membrane that
act like pumps.
Many cells use such proteins to
move calcium, potassium, and
sodium ions across cell membranes.
Changes in protein shape
seem to play an important role in the pumping process.
Lesson Overview Life Is Cellular
Endocytosis
- Endocytosis: the process
of taking material into the
cell by means of
infoldings, or pockets, of the cell membrane
- The pocket that results breaks
loose from the outer portion of
the cell membrane and forms a
vesicle or vacuole within the
cytoplasm.
Lesson Overview Life Is Cellular
Endocytosis
Large molecules, clumps of food,
and even whole cells can be taken
up by endocytosis.
Two examples of endocytosis are
phagocytosis and pinocytosis.
Lesson Overview Life Is Cellular
Endocytosis
- Phagocytosis: extensions of cytoplasm surround a
particle and package it within a food vacuole. The cell then engulfs it.
Lesson Overview Life Is Cellular
Endocytosis
- pinocytosis: cells take up liquid from the surrounding
environment by forming tiny pockets along the cell membrane.
-The pockets fill with liquid
and pinch off to form vacuoles
within the cell.
Lesson Overview Life Is Cellular
Exocytosis
- Exocytosis: release large amounts of material from the cell
- the membrane of the vacuole surrounding the
material fuses with the cell membrane, forcing the contents out of the cell
Lesson Overview Life Is Cellular
Mystery Clue #2
• As Michelle ran, she perspired, losing salts from her bloodstream.
• And as she drank more and more water during the race, the concentration of dissolved salts and minerals in her bloodstream decreased.
• How do you think these phenomena contributed to Michelle’s condition?
Homeostasis and Cells
Section 7.4
Freshwater diatoms – unicellular algae with hard silica cell
wall – come in many shapes and sizes.
Lesson Overview Life Is Cellular
The Cell as an Organism
- Homeostasis: relatively constant internal physical and chemical condition
- To maintain homeostasis unicellular organisms:
- grow
- respond to the environment
- transform energy
- reproduce.
Lesson Overview Life Is Cellular
Cell Specialization
- The cells of multicellular organisms are specialized, with different cell types playing different roles
Lesson Overview Life Is Cellular
Levels of Organization
- A tissue is a group of similar cells that performs a particular function
Lesson Overview Life Is Cellular
Levels of Organization
- Organ: many groups of tissues working together to perform complicated tasks
Lesson Overview Life Is Cellular
- Organ System: a group of organs that work together to perform a specific function
- For example, the stomach, pancreas, and intestines work
together as the digestive system.
Levels of Organization
Lesson Overview Life Is Cellular
Cellular Communication
- Types:
- Chemical Signals: passed from one cell to another that speed up or slow down the activities of the cell
- Cellular Junctions: connections formed to neighboring cells
- Some junctions allow small molecules that carry chemical messages to pass directly from one cell to another
- Receptor: molecule that the signaling molecule binds to on the cell membrane; receives messages from other cells
Lesson Overview Life Is Cellular
Solve the Chapter Mystery: Death by…Water
• During the race, Michelle drank plenty of water, but she didn’t replace the salts she lost due to sweating.
• As a result, her blood became hypotonic, and osmotic pressure led the cells in her brain (and throughout her body) to swell.
• As Michelle’s blood became more dilute, cells in her brain sent chemical signals to her kidneys to stop removing sodium chloride and other salts from her bloodstream.
• However, as she continued to sweat, she continued to lose salt through her skin.
• By the end of the race, Michelle had lost a large quantity of salt and minerals and had taken in so much water that homeostasis had broken down, and her cells were damaged by unregulated osmotic pressure.
• When Michelle was rushed to the hospital, the doctors discovered that she was suffering from hyponatremia, or water intoxication.
• Left untreated, this condition can lead to death.
Lesson Overview Life Is Cellular
Solve the Chapter Mystery: Death by…Water
1. When a person sweats, water and essential solutes called electrolytes are lost from body fluid. Michelle drank lots of water but did not replace lost electrolytes. What effect did this have on her cells?
1. Had Michelle alternated between drinking water and a sports drink with electrolytes would her condition be the same?
1. Do you think that hyponatremia results from osmosis or active transport? Explain your reasoning.
1. Explain how hyponatremia disrupts homeostasis in the body.