Transcript 2. An Overview of the Cell

An Overview of the
Cell
With a focus on Plant and Animal Cell
Structures
Types of Cells
O There are two categories all cells can be divided
into:
O Prokaryotic cells do not have a membrane-bound
nucleus and the genetic material is scattered
throughout the rest of the cell. (doesn’t have a true
nucleus)
O Eukaryotic cells have a nucleus surrounded by a
nuclear membrane to contain all genetic material.
(has a true nucleus)
O Cells vary in size, shape and function.
Prokaryotic vs Eukaryotic Cells
The Nucleus
O Is the cell’s control center and coordinates all cell
activities.
O The nucleus contains chromosomes which are
threadlike structures that contain our genetic code.
These chromosomes are made of proteins and
deoxyribonucleic acids (DNA)
O Chromatin: The complex of DNA and proteins that make
up a eukaryotic chromosome. When the cell is not
dividing, chromatin exists as a mass of long thin fibres
that are not visible with a light microscope.
O Chromosomes: As the cell prepares to divide
(reproduce), the stringy, entangled chromatin coils up
and becomes thick enough to be seen as separate
structures called chromosomes.
The Nucleus (and Rough Endoplamic Reticulum)
The Nuclear Membrane
• Separated from the rest of the cytoplasm by a double
membrane. Pores in the nuclear envelope allows RNA
and other chemicals to pass through but keeps the
DNA inside
Nucleolus
O A small spherical structure located inside the
nucleus.
O It is believed that the nucleolus creates ribosomal
ribonucleic acid (rRNA) which directs the formation
of ribosomes.
The Cell Membrane
O The cell membrane (plasma membrane)
surrounds the cell, giving it a definite shape
and boundary. It is selectively permeable,
so it controls what enters and exits the cell.
Cell Wall
O In many organisms the plasma membrane is not
the outermost boundary.
O In plants, most algae, fungi and bacteria, there is
a cell wall that lies outside the plasma
membrane.
O In plants it is made of cellulose and has spaces
for water, ions and particles to pass through.
O It is NOT selectively permeable but does offer
protection and support for the cell.
• Some plant cells have an additional secondary
wall with a middle lamella in between that
contains a sticky pectin to hold cells together.
The Cytoplasm
O The cytoplasm is the gel-like substance
inside the cell.
O Cytoplasm - 70% water
- 30% proteins, fats,
carbohydrates and other ions.
O Composition is always changing due to
osmosis and diffusion.
O The cytoplasm houses the working “organs”
of the cell called organelles.
Mitochondria
O Mitochondrion (singular)
Mitochondria (plural)
O Are oval-shaped organelles and are the
“powerhouses” of the cell.
O Mitochondria contain their own DNA
O They provide the body with needed energy in
a process called cellular respiration.
O Sugar molecules are combined with oxygen to form
carbon dioxide and water with a release of energy.
O Energy is not made in the mitochondrion rather the
breakdown of glucose sugar releases energy.
O Energy is available for processes such as:
O Muscle contraction
O Synthesis of new molecules
O Cellular transport
O Two separate
membranes – a
smooth outer
membrane and a
folder inner
membrane.
O Cristae – fingerlike
projections of the
folded inner
membrane. Each
contains special
enzymes to help
breakdown glucose.
Ribosomes
O Smallest organelle in the cell.
O Site of protein synthesis.
O Proteins are the molecules that makes up
cell structure.
O Cell growth and reproduction require
constant synthesis of proteins.
O In the nucleus, DNA sends messenger
molecule to produce protein in ribosomes of
the cell.
O Location: found
both scattered
throughout the
cytoplasm and
attached to
endoplasmic
reticulum.
Endoplasmic reticulum
A series of canals that carry materials
throughout the cytoplasm.
Composed of parallel membranes.
2 types:
O
O
O
1.
2.
Rough endoplasmic reticulum
Smooth endoplasmic reticulum
Rough Endoplasmic
Reticulum
O Organelle with a double membrane and ribosomes
attached.
O Extends from the nuclear membrane to the cell
membrane.
O Transports proteins made by the ribosomes to the
Golgi apparatus.
Smooth Endoplasmic
Reticulum
O Double membrane bound organelle without
ribosomes.
O Also extends throughout the cell.
O Produces lipids for the cell.
Golgi Apparatus
O Appears like a stack of pancakes.
O They are membranous sacs piled on top of
each other.
O Function:
O To package , modify and store proteins
produced by ribosomes on the rough
endoplasmic reticulum.
O To release large molecules (hormones,
enzymes) by exocytosis.
O Golgi apparatus migrates towards the
plasma membrane where small packets
(called vesicles) are released and pass
through plasma membrane by exocytosis.
O The golgi apparatus will also form
lysosomes
Lysosomes
O Formed by exocytosis of vesicles from Golgi
apparatus and are smaller than
mitochondria.
O They are sac-like structures that contain
digestive enzymes to break down large
molecules and cell parts within the
cytoplasm.
O Only found in animal cells
O Purpose:
O The break down cell “food” to use as an energy
source.
O As a defense mechanism for the immune
system.
O The Immune Response
O Lysosomes destroy harmful substances that
find their way into the cell.
O Example: White blood cells phagocytise foreign
particles. Lysosomes then release digestive
enzymes to destroy the invader.
O Lysosomes are also known as “suicide sacs”.
O Body cells have a certain lifespan after
which they die and must be cleaned up.
Digestive enzymes in lysosomes clean up
cell parts after body cells die.
Vacuoles
O Vacuoles are fluid-filled, membrane-bound
structures that store substances produced
by the cell for future use.
O They are reservoirs for sugars, minerals,
proteins, water and wastes.
O Gives plant cells physical support.
O Plant cells have large,
central vacuoles.
O Animal cells have many
smaller vacuoles.
Cytoskeleton
O Microfilaments are
threadlike structures in the
cytoplasm that help provide
shape & movement.
O Microtubules are tube-like
fibres (made of protein)
that transport materials
through the cytoplasm –
also found in flagella &
cilia.
Cilia and Flagella
O A flagellum is a whip like tail
O that aids in movement
O Flagella spin like a propeller
O Cilia (cilium)are shorter, hair like
structures that aid in movement
and moving materials.
Centrioles
O Composed of nine bundles of three
microtubules.
O Found only in animal cells.
O Play a key role in cell division.
Plastids
O Plastids are “chemical factories” and
O
O
O
O
“storehouses” for food and other pigments in
plant cells
Only found in plant cells!
Chloroplasts are plastids that contain the green
pigment chlorophyll that is used for
photosynthesis.
Chromoplasts- store orange and yellow pigments
Amyloplasts- colourless plastids that store starch
O Plastid structure:
O Made of a double membrane
O Packets of chlorophyll inside which taps into the
Sun’s energy to make sugar.