STRUCTURE AND FUNCTION OF

CELLS

Objectives1. Describe the structures and functions of cell components.

1.1 Review evidence for the existence of cells.

1.2 Observe, sketch, and describe a representative sampling of plant and animal cells.

1.3 Describe the structure of a cell membrane.

1.4 Describe the functions of the organelles found in eukaryotic cells.

1.5 Contrast the structure of prokaryotic and eukaryotic cells.

The Cell Theory•There are four generalizations that

1. All organisms are made up of cells, whether unicellular (single cell) or multicellular (many cells). That is, cells are the basic structural units making up all bodies

2. All processes common to living organisms occur in the individual cells or that individual cells had to carry out basic functions necessary to maintain the life of the entire organism (such as respiration, excretion, ingestion and others)

3. New cells arise from exhisting cells4. Cells contain hereditary material, which

ensures the passing of specific characteristics from parent to daughter cells

Cell Structure •There is no “normal” or “typical cell which can be used as a common representative for all organisms. Differences exist in cell size, shape, colour and the kind of organisms but also within individual organisms.

•In order to study cells we combine all the possible features of a cell into one “master” cell which we study as a model. It should be emphasized that a cell like this would not really exist under natural conditions

Prokaryotes vs. Eukaryotes

• Prokaryotes and Eukaryotes are the two major types of cells.

What’s the difference between prokaryotes and eukaryotes?•Prokaryotic cells were here first and for billions of years were the only form of life on Earth. All prokaryotic organisms are unicellular

•Eukaryotic cells appeared on earth long after prokaryotic cells but they are much more advanced. Eukaryotic organisms unlike prokaryotic can be unicellular or multicellular.

Characteristics of Prokaryotes•Prokaryotes are the simplest type of cell. •Oldest type of cell appeared about four billion years ago.

•Prokaryotes are the largest group of organisms •Prokaryotes unicellular organisms that are found in all environments.

•Prokaryotes do not have a nuclear membrane . Their circular shaped genetic material dispersed throughout cytoplasm.

•Prokaryotes do not have membrane-bound organelles.

•Prokaryotes have a simple internal structure. •Prokaryotes are smaller in size when compared to Eukaryotes.

Shapes of Prokaryotes

•Cocci = spherical (round)

•Bacillus = (rod shaped)

•Spirilla = helical (spiral)

What do prokaryotic cell look like?

Characteristics of Eukaryotes•Eukaryotic cells appeared approximately one billion years ago

•Eukaryotes are generally more advanced than prokaryotes

•Nuclear membrane surrounds linear genetic material (DNA)

•Unlike prokaryotes, eukaryotes have several different parts.

•Eukaryote’s organelles have coverings known as membranes.

•Eukaryotes have a complex internal structure.

•Eukaryotes are larger than prokaryotes in size .

What do eukaryotic cells look like?

MitochondriaNucleus

Golgi Complex

Endoplasmic Reticulum

Cell Membrane

Cytoplasm

How do the differences line up?Prokaryotes

• Organelles lack a membrane

• Ribosomes are the only organelles

• Genetic material floats in the cytoplasm (DNA and RNA)

• Circular DNA

• Unicellular

• Cells are smaller in size

• Has larger number of organisms

• Appeared 4 billion years ago

Eukaryotes

• Organelles covered by a membrane

• Multiple organelles including ribosomes

• Membrane covered Genetic material

• Linear DNA

• May be multicellular or unicellular

• Cells are larger in size

• Has smaller number of organisms

• Appeared 1 billion years ago

How do the similarities line up?

• Both types of cells have cell membranes (outer covering of the cell)

• Both types of cells have ribosomes

• Both types of cells have DNA

• Both types of cells have a liquid environment known as the cytoplasm

Organelles of Eukaryotic Cells•With few exceptions eukaryotic cells of most organisms show three recognizable parts or divisions:1. Cell wall and/or cell membrane2. Cytoplasm3. Nucleus

•As we go through these notes colour in the organelles we talk about on the handout

Cell (or Plasma )Membrane• Surrounding both plant and

animal cells is a thin, flexible and living plasma membrane

• It consists of two rows (or a bilayer)of lipid molecules and proteins. Some proteins are associated with one layer and some with both layers.

• The outer part of a phospholipid molecule is hydrophilic (water loving) while the inner part of the chain, or the tail is hydrophobic (water fearing). This characteristic enables a membrane to maintain a moist exterior while offering some barrier to movements of molecules through it.

Plant Cells•Cell Wall – Support and protection

•Endoplasmic reticulum – manufacturing and storage area as well as a transport system

•Chloroplast (Plastids) - Their main role is to conduct photosynthesis, where the photosynthetic pigment chlorophyll captures the energy from sunlight

•Golgi Complex – Secreting, “packaging” and storing various substances as well as transport

•Vacuole – Storage or holding area for water, food, salts and wastes

Plant Cells

•Ribosome – Arranges amino acids into protein

•Nucleolus – consists of proteins and nucleic acids which direct or take part in protein synthesis

•Mitochondria – Releases energy for cell use. The “powerhouse”

•Nucleus – Directs the synthesis or reproduction of proteins

•Cell membrane – Regulates movements of substances in and out of a cell

•Cytoplasm – contains the organelles and the numerous substances taking part in, or which are the result of, various life- sustaining actions

Animal Cells

Centrosome – Contains centrioles which take part in animal cell reproduction Smooth Endoplasmic Reticulum - synthesizes lipids, phospholipids, and steroidsRough Endoplasmic Reticulum -has ribosomes attached to it and is the site of protein synthesis. it then takes the proteins it creates and transports them to the GolgiRibosome – Arranges amino acids into proteinsCentriole - are found in pairs and move towards the poles (opposite ends) of the nucleus when it is time for cell division

Animal Cells

Mitochondria – Releases energy for cull use. The “powerhouse”Lysosome – Encloses powerful digestive enzymesVacuole – Storage or holding area for water, food, salts or wastesGolgi Complex – Secreting, “packaging” and storing substances, as well as transportNucleus – Directs the synthesis or reproduction of proteins, where chromosomes are locatedNucleolus - consists of proteins and nucleic acids which direct or take part in protein synthesis

Your turn:

•Make a Venn Diagram outlining the similarities and differences between prokaryotes and eukaryotes

•Make a second Venn Diagram outlining the similarities and differences of plant and animal cells

•You may use your book and/or consult your friend