cell structure and function life is cellular. prokaryotes and eukaryotes – cells come in many...

CELL STRUCTURE AND FUNCTION

LIFE IS CELLULAR

LIFE IS CELLULAR

• Prokaryotes and Eukaryotes– Cells come in many sizes and shapes.• Typical size 5 to 50 micrometers• Tiniest mycoplasma bacteria is 0.2 micrometers across• Giant amoeba Chaos chaos is 1000 micrometers (µm) in

diameter.

– All cells have two things in common.• They are surrounded by a barrier called a cell membrane.• They contain the molecule that carries biological

information-DNA.

MYCOPLASMA BACTERIA

CHAOS CHAOS AMOEBA

LIFE IS CELLULAR

– Cells are one of two categories, depending on whether they contain a nucleus or not.• The nucleus (plural is nuclei) is a large membrane-

enclosed structure that contains the cell’s genetic material in the form of DNA.– The membrane is a thin layer of material that serves as a

covering or lining.

• The nucleus controls many of the cells activities.• Eukaryotes are cells that contain nuclei.• Prokaryotes are cells that do not contain nuclei.

LIFE IS CELLULAR

– Prokaryotes• These cells are usually smaller.• They have genetic material that is not contained in a

nucleus.• Despite being simpler cells, they carry out every activity

associated with living things.– They grow– They reproduce– They respond to the environment– They move by gliding along a surface or swim through liquids– Bacteria are prokaryotes

PROKARYOTES

LIFE IS CELLULAR

– Eukaryotes• These cells are larger and more complex.• They contain many structures and membranes, and are

highly specialized.• They contain a nucleus in which their genetic material

is separated from the rest of the cell.• Some are single celled and other are multicellular.• Plants, animals, fungi are eukaryotes.

EUKARYOTES

EUKARYOTIC CELL STRUCTURE

• Comparing the Cell to a Factory– The cellular structure of a eukaryotic cell seems, at

first glance, to be very complex.– However, after looking at the cell under a

microscope, patterns begin to emerge.– Organelles are within the eukaryotic cell and act

like specialized organs, or organelles, “little organs.”

EUKARYOTIC PLANT CELL

EUKARYOTIC ANIMAL CELL


– The cell is divided into two parts• The nucleus• The cytoplasm

– The cytoplasm is the portion of the cell outside the nucleus.

• Nucleus– The nucleus is the control center of the cell.– The nucleus contains nearly all the cell’s DNA and

with it the coded instructions for making proteins and other important molecules.

CELL NUCLEUS


– The nucleus is surrounded by the nuclear envelope.• This is composed of 2 membranes.• This has thousands of pores allowing material to move in

and out of the nucleus.– Allows RNA, proteins, and other molecules to move through the

pores.

– The granular material in the nucleus is the chromatin.• This consists of DNA bound to protein.• When cells divide, the chromatin condenses to form

chromosomes.– Contain the genetic information passed from one cell to next.


– The nucleolus is in the nucleus and is where the assembly of ribosomes takes place.

• Ribosomes– Proteins are assembled on ribosomes.– Ribosomes are small particles of RNA and protein

found in the cytoplasm.• This turns out proteins on instructions that come from

the nucleus.


• Endoplasmic Reticulum– This is an internal membrane system where lipid

components of the cell membrane is assembled, along with proteins and other materials that are exported from the cell.

– The rough ER is where proteins are produced.• Ribosomes are found on its surface.

– No ribosomes are found on the smooth endoplasmic reticulum.

ENDOPLASMIC RETICULUM


• This contains enzymes that synthesize membrane lipids and detoxify drugs.– Liver cells contain a lot of smooth ER since this is where most of

the drugs are detoxified.

• Golgi Apparatus– Proteins produced in the rough ER move into an

organelle called the Golgi apparatus.– The function of the Golgi apparatus is to modify,

sort, and package proteins and other materials from the endoplasmic reticulum for storage in the cell or secretion outside the cell.

GOLGI APPARATUS


• The Golgi apparatus is where the finishing touches are put on the proteins before they leave the production area.

• Lysosomes– These are the cleanup crew.– These are small organelles filled with enzymes

that digest, breakdown, lipids, carbohydrates, and proteins into small molecules that can be used by the rest of the cell.


– Lysosomes also breakdown organelles that have outlived their usefulness.

– They remove “junk.”– Tay-Sachs disease can be traced to the failure of

the lysosomes.• Vacuoles– This is the storage area.– These are sac-like structures that store water,

salts, proteins, and carbohydrates.

LYSOSOMES

VACUOLES


• These also can pump water in and out of the cell to maintain homeostasis which controls the internal environment.

• Mitochondria and Chloroplasts– Mitochondria• Mitochondria are organelles that convert the chemical

energy stored in food into compounds that are more convenient for the cell to use.• These have an inner and outer membrane.• These are inherited, in humans, from the ovum or egg.


– Chloroplasts• Chloroplasts are organelles that capture the energy

from sunlight and convert it into chemical energy in a process called photosynthesis.• Chlorophyll is contained here.

– Organelle DNA• Chloroplasts and mitochondria contain their own

genetic information in the form of small DNA molecules.

MITOCHONDRIA

CHLOROPLASTS

CHOROPLASTS


• Cytoskeleton– The supporting structure of the cell is the

cytoskeleton.– The cytoskeleton is a network of protein

filaments that helps the cell to maintain its shape. The cytoskeleton is also involved in movement.• Made up of protein filaments

– Microfilaments– Microtubules


• Microfilaments support the cell and allow cells such as amoebas to move.• Microtubules help to maintain cell shape

– Also help in cell division with structures known as centrioles.– Help to build cilia and flagella that enable the cell to swim

rapidly in liquids.

CYTOSKELETON

CELL BOUNDARIES

• Diffusion– In solutions, particles move constantly.– Particles collide with one another and spread out

randomly.– Particles move from areas where they are more

concentrated to areas where they are less concentrated, also known as diffusion.

– They do this until the concentration of particles is the same throughout the system, known as equilibrium.

CELL BOUNDARIES

– Because diffusion depends upon random particle movements, substances diffuse across membranes without requiring the cell to use energy.

– After equilibrium is reached, there is still movement of particles across the cell membrane but the movement is equal in both directions.

DIFFUSION

CELL BOUNDARIES

• Osmosis– Some substances might be too large or too

charged to cross the cell membrane (lipid bilayer).– Membranes that are permeable indicates that

substances can diffuse across it. – Impermeable membranes are those that

substances cannot diffuse across.– Most biological membranes are selectively

permeable.

CELL BOUNDARIES

– Water passes through quite easily while some solutions cannot.

– Osmosis is the diffusion of water through a selectively permeable membrane.

– How Osmosis Works• Take the example of a beaker with a permeable

membrane in the middle. On one side is a low concentration of sugar water, on the other is a high concentration of sugar water. Water will move from the higher concentration (water) to the lower concentration (water + sugar) across the membrane.

CELL BOUNDARIES

• The membrane is permeable to water but not to sugar.• This movement of water will occur until there is an

equilibrium, or an equal amount on both sides of the membrane of water and sugar.• When this happens, the two solutions are said to be

isotonic (same strength).• The more concentrated solution is hypertonic (above

strength) and the less concentrated solution is hypotonic (below strength).

OSMOSIS

LEVELS OF CELL ORGANIZATION


• The levels of organization in a multicellular organism are individual cells, tissues, organs, and organ system.

• Tissues– In multicellular organisms, cells are the first level

of organization.– Similar cells are grouped into units called tissues.– A tissue is a group of similar cells that perform a

particular function.


– Most animals have four main types of tissue• Muscle• Epithelial• Nervous• Connective tissue

• Organs– Many types of tissues work together as an organ.

• The tasks of the body are too complex for just one type of tissue to perform the task.

• Each type of tissue performs an essential task to help the organ function.


• Organ Systems– A group of organs that work together to perform a

specific function is called an organ system.– Specialized cells such as nerve and muscle cells

are able to function precisely because other cells are specialized to obtain the food and oxygen needed by those cells.

– This overall specialization and interdependence is one of the remarkable attributes of living things.

cell structure and function life is cellular. prokaryotes and eukaryotes – cells come in many...

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