Download Cell_Structure_Function.d oc

Cell Structure and Function
Do Now: All living things are made up of cells. Some organisms are composed of
only one cell. Other organisms are made up of many cells. What are the advantages
of one-celled organisms? What are the advantages of organisms made up of many
cells?
Unicellular: simpler needs, respond to environment immediately because entire cell is
immersed in the environment.
Multicellular: different jobs are divided among different groups of cells that work
together. Will continue to survive even if it loses some its cells.
Late 1600s – Anton Van Leeuwenhoek – one of the 1st to use a microscope and view
living cells
Robert Hooke coined the term “cells” after viewing cells under a light microscope and
thinking that they resembled the chambers of a monastery.
Part of the cell theory states that cells are the basic unit of all life.
The Cell Theory states:
 All living things are composed of cells.
 Cells are the basic units of structure and function in living things.
 New cells are produced from existing cells.
Basic Cell Structure
Can be of many sizes and shapes (always very small).
All cells have certain basic structures:
Cell membrane – thin, flexible barrier around cell
Cell wall – some cells have a strong layer around the cell membranes to protect cells
Nucleus – structure that contains cell’s genetic info and controls activity of the cell
Cytoplasm – material inside cell membrane that contains many other structures
Prokaryotes vs. Eukaryotes
The cells of Prokaryotes only have cell membranes and cytoplasm –
NO NUCLEUS!
All bacteria are prokaryotes – Ex. Escherichia coli, contained in the intestine.
Eukaryotes contain nuclei. These types of cells also contain lots of other specialized
structures, called organelles – that perform cellular functions. Eukaryotes can live as
single celled organisms, but they’re usually found as multicellular organisms.
7-2 Cell Structures
Activity 7-2 Interest Grabber – parts of a computer
Cell walls can be found in any type of cell EXCEPT animal cells. Even prokaryotic
cells may contain a cell wall at times. Most cell walls are made of the fibers of
carbohydrates and proteins. Plant cell walls are made mostly of cellulose, a tough
carbohydrate fiber. Paper is made up of cellulose!
Nucleus holds the coded instructions for making proteins and other important
molecules. The nucleus is important because making proteins is one of the main jobs
of the cell.
 Chromatin – the granular material visible within the nucleus – consists of
DNA bound to protein
 Chromosomes – form when a cell is about to divide and chromatin condenses
– passes along genetic info to subsequent cells
 Nucleolus – small dense region in nucleus responsible for the beginning of
production of ribosomes (which make proteins)
 Nuclear envelope – double membrane layer around the nucleus that contains
thousands of pores to allow for exchange of material (Ex. RNA)
Cytoskeleton is a structure that some cells contain to keep their shape. Involved in
cell movement.
 Microtubules – hollow tubes of protein about 25 nanometers in diameter –
maintain cell shape and provide “tracks” on which organelles move about.
Important in cell division b/c they form centrioles (plants don’t have
centrioles)
2
 Microfilaments – long, thin fibers that function in movement and support
the cell – about 7 nanometers in diameter
Organelles in the Cytoplasm
Ribosomes:
 Small particles made up of RNA and protein
 Proteins are assembled ON ribosomes (site of protein synthesis)
 0.025 micrometers in diameter
 Produce proteins following coded instructions from nucleus
Endoplasmic Reticulum:
 Internal membrane system
 Components of cell membrane are assembled
 Proteins are modified
 Rough ER is involved in protein synthesis b/c it is studded with ribosomes
 Proteins made from these ribosomes move directly into rough ER for
chemical modification
 Smooth ER (no ribosomes) contains a collection of enzymes that perform
specialized tasks: synthesis of lipids
Golgi Apparatus:
 Named for Italian biologist Camillo Golgi
 Enzymes in GA attach carbohydrates and lipids to proteins
 From here, proteins are sent to final destination
Lysosomes:
 Small organelle
 Filled with enzymes
 Break down lipids, carbohydrates and proteins from food into particles that can
be used by the rest of the cell
 Help break down dead organelles
 Removes debris that might otherwise clutter up cell
Vacuoles:
 Saclike structure
 Stores material such as water, salt, proteins, and carbohydrates
3
 Some plant cells have 1 central vacuole – pressure in these vacuoles make it
possible to support heavy structures such as leaves and flowers
 Also found in single-celled organisms
 aka vesicles when they are small and transport substances within the cell
Chloroplasts:
 Found in plant cells and some algae and bacteria
 Not contained in animal or fungal cells
 Use sunlight to make energy-rich food molecules in a process known as
photosynthesis
 Enclosed by 2 envelope membranes
 Green pigment chlorophyll is located in the photosynthetic membranes
(thylakoids)
Mitochondria:
 Release energy from stored food molecules
 Use energy from food to make high-energy compounds that the cell uses to
power growth, development, and movement
 Enclosed by 2 envelope membranes – inner membrane is folded
Organelle DNA
 Chloroplasts and mitochondria contain some of their own DNA that is
essential for normal functioning of both organelles
 Nearly all mitochondria are inherited from the cytoplasm of the ovum (mother)
– first cousins from sisters share the same mitochondrial DNA
The Cell as a Factory
P 182 description
Comparing Cells
Look at comparison chart on p 183
Assignment: Assign one organelle to each student and ask to be creative and write
the function in it.
4
7-3 Movement Through the Membrane
Cell membrane – lipid bilayer
 The core is a double-layered sheet called a LIPID BILAYER
 Gives cell membrane a tough, flexible structure that forms a strong barrier
btwn the cell & its surroundings
 Contain, lipids, proteins, carb chains
 Some proteins form pumps or channels to help material move in and out of
cell
Diffusion
 Cell membranes are surrounded by liquid on the inside and the outside
 The liquidy cytoplasm is a solution made up of many substances plus water
 The concentration of a solution is the mass of solute in a given volume of
solution
 In a solution, molecules move constantly – they collide and also spread out
 Tend to move from high concentration to low concentration – known as
diffusion
 When the concentration of the solute is the same throughout a solution, the
system has reached equilibrium
 Diffusion causes many substances to move across a cell membrane
without using energy
Osmosis
 Not all substances can cross biological membranes
 This is known as selective permeability
 A membrane is said to be “permeable” to those substances it allows in
 A membrane is said to be “impermeable” to those substances it does not allow
in
 Osmosis is the process by which water molecules are allowed to pass
easily through most selectively permeable biological membranes
5
Osmotic Pressure
 See chart on p 187
 Because most cells contain sugars, salts and proteins, they are hypertonic to
fresh water
 Animal cells are bathed in fluid such as blood which is isotonic to cell
concentrations
 Plant and bacteria cells do come in contact w/ fresh water but have a strong
cell wall that prevents them from expanding – however, this increased pressure
makes cell very vulnerable to injury
 Other cells, like single-celled organisms use a pump – in the form of a
contractile vacuole to rhythmically pump excess water out of the cell – ex. of
homeostasis
 Isotonic, Hypotonic, Hypertonic
Facilitated Diffusion
 The molecules that can’t diffuse directly through the cell membrane use protein
channels of a protein in the cell membrane to pass through
 Fast and specific but will only occur if there is a concentration of higher/lower
molecules
 This does NOT require energy because it is still considered diffusion
Active Transport
 Requires energy
 Moves something against the gradient from lower to high concentrations
 Ex. Sodium/Potassium pumps in animal cells – you want sodium outside the
cell and potassium inside so you need a pump to work against diffusion
 Large amounts of material are transported through movement of the cell
membrane – ENDOCYTOSIS is the process of taking material into the cell by
means of in-folding or pockets – breaks loose from cell membrane and
becomes vacuole
 When large particles are taken in it’s called PHAGOCYTOSIS
 The removal of large amounts of material from the cell is known as
EXOCYTOSIS – the membrane of the vacuole fuses with the cell membrane
and forces the material out of the cell
6
7-4 Diversity of Cellular Life
Unicellular organisms
 Are single-celled living organisms that do everything you would expect a living
thing to do.
Examples:
 yeast,
 volvox aureus,
 leptospira interrogans - a zoonotic disease transmitted from dogs, livestock,
and wild mammals. The organisms can establish a commensal relationship with
many animal hosts, persisting in the renal tubules without producing disease or
causing pathologic changes in the kidney. From here they are continually
excreted in the urine and can contaminate natural bodies of water which serve
as a source of the infection. The organism penetrates intact mucous
membranes or burrows through small breaks in the skin to enter the blood
stream. From there it is disseminated to all parts of the body including the
meninges, liver, and conjunctiva. In the summer of 1998 there was an outbreak
of leptospirosis among athletes that participated in a triathlon in Illinois. 110
athletes became ill and 23 were hospitalized. The outbreak was traced to Lake
Springfield and a warning was issued not to swim, water ski or use personal
watercraft in this lake. Virulence factors of the organism are unknown but
hypothesized to be hyaluronidase and burrowing motility. The mechanism of
damage may be via the host immune response.
Multicellular Organisms
 Cells of these organisms are interdependent like players on a team – each player
has a function that contributes to the success of the team
 Cell specialization – term used to describe idea above (liver cells, heart muscle
cells, etc.)
More examples:
 Red blood cells – carry oxygen molecules once they eject nucleus
 Pancreatic cells – specialized to produce protein enzymes that make it possible
to digest food, so they have enormous amounts of the organelles involved in
protein synthesis – rough ER, Golgi apparatus, clusters of vacuoles loaded with
stored protein
 Nerve cells – sends impulses
 Muscle cells – contract/relax to create movement – lots of mitochondria
7
Levels of Organization
 Cells – specialized cells obtain food and oxygen & carry out specific function
 Tissues – a group of similar cells that perform a particular function
 Most animals have 4 main types of tissue: (1) muscle, (2) epithelial (skin),
(3) nervous and (4) connective tissue (bone, blood, cartilage, and lymph)
 Organs – many tissues work together to perform a function (ie) A Muscle =
muscle tissue, nerve tissue and connective tissue
 Organ Systems – group of organs working together to perform a specific task
(ie) digestive system, nervous system, circulatory system
8