THE CELL
(eukaryotic)
The IB Biology Juniors
Nucleus
• Definition: Region of the cell containing chromosomes, surrounded by a double
membrane, in which there are pores; provides for storage and protection of
chromosomes; contains DNA and RNA
• Functions
• Stores hereditary material referred to as chromatin
• Stores proteins and RNA in the nucleolus
• Site for transcription in which mRNA is produced
• Site for exchange of hereditary molecules (DNA and RNA) between the nucleus
and the rest of the cell
• During the cell division, chromatins are arranged into chromosomes in the
nucleus
• Production of ribosomes in the nucleolus
• Selective transportation of regulatory factors and energy molecules through
nuclear pores
The nucleus is like the brain of the cell.
Left Cell: Undergoing Mitosis; Right and Central Cells are in interphase
Structure/Contents
• Nuclear Membrane: Double-layered structure that encloses the contents of the
nucleus; The outer layer is connected to the endoplasmic reticulum
• Nuclear Pores: The nucleus communicates with the remaining of the cell or the
cytoplasm through several openings called nuclear pores; Such nuclear pores are
the sites for exchange of large molecules (proteins and RNA) between the nucleus
and cytoplasm
• Chromosomes: Present in the form of strings of DNA and histones
(proteins) called chromatin
• Nucleolus: A dense, spherical-shaped structure present
inside the nucleus; Produces ribosomes; Disappears when
a cell undergoes division and is reformed after the completion
of cell division
Miscellaneous
• Prokaryotic vs. Eukaryotic
DNA is stored in the nucleus of eukaryotic cells. Prokaryotic cells lack a
nucleus. Their DNA is located in an area of cytoplasm called the nucleoid
region.
• Transcription
This nucleus contains the genetic materials such as DNA and RNA. These
materials actively participate in the process of protein synthesis. The DNA
transcription takes place inside the nucleus. In the process mRNA is
formed. Then the transcribed mRNA comes out of the nucleus pore into
the cytoplasm. The translation process takes place and thus completes the
process of protein synthesis.
• Haploid/Diploid Differences – See Next Slide
Haploid an Diploid refer to the number of chromosomes in a cell. Haploid cells have one set of chromosomes
and diploid cells have two sets. Humans have 46 chromosomes or 23 pairs. One set of each pair comes from the
mother, and the other from the father. The only haploid cells in the human body are gametes (sperm/egg cells).
All other cells in the human body are diploid cells. For a more thorough explanation:
http://www.youtube.com/watch?v=1yu1Zuy_uEQ
Endoplasmic Reticulum
• Definition: The endoplasmic reticulum is a network of membranous
tubules within the cytoplasm of a eukaryotic cell, continuous with the
nuclear membrane. It usually has ribosomes attached and is involved in
protein and lipid synthesis.
• It takes up more than 10% of the cell, partially surrounding the nucleus.
• The endoplasmic reticulum manufactures, processes, and transports a wide
variety of biochemical compounds for use inside and outside of the cell.
Some proteins are simply wandering, and some are known as ‘resident
proteins’, which are constantly trapped in the lumen. The resident proteins
contain a specialized retention signal consisting of a specific sequence of
amino acids that enables them to be retained by the organelle.
Rough ER vs. Smooth ER
Rough ER
Smooth ER
• The surface of the rough ER is covered with
ribosomes, making it look bumpy under a
microscope.
• It is directly continuous with the nuclear
envelope.
• Its job is to produce proteins that will be
secreted from the cell.
• The ribosomes assemble amino acids into
protein units, which are transported into the
rough endoplasmic reticulum for further
processing. These proteins may be either
transmembrane proteins, which become
embedded in the membrane of the
endoplasmic reticulum, or water-soluble
proteins, which are able to pass completely
through the membrane into the lumen.
• The smooth ER is from where most proteins
exit the ER from the vesicles.
• It is much smaller than the rough ER.
• Smooth endoplasmic reticulum is chiefly
involved, however, with the production of
lipids (fats), building blocks for carbohydrate
metabolism, and the detoxification of drugs
and poisons.
• It stores calcium which is involved in calcium
metabolism. In muscle cells, smooth
endoplasmic reticulum releases calcium to
trigger muscle contractions.
Micrograph vs. Representation Images
Ribosomes
Structure and Function
• Do not have an exterior membrane
• Carry out protein synthesis in the cell
• Structures maybe found in the cytoplasm
• May be attached to the surface of endoplasmic reticulum
• Composed of a type of RNA and protein
Prokaryotic vs. Eukaryotic Cells
Ribosomes
• Ribosomal subunits are synthesized by the nucleolus
• Ribosomes of eukaryotic cells are larger and denser than prokaryotic
• Eukaryotic and prokaryotic ribosomes are composed of two subunits
• The eukaryotic two subunits are 80S
• The prokaryotic two subunits only equal 70S
• These two subunits join together when the ribosome attaches to
messenger RNA (mRNA) during protein synthesis
• Ribosomes along with another RNA molecule, transfer RNA (tRNA),
help to translate the protein-coding genes in mRNA into proteins.
Proteins Produced: Free vs. Bound
Free Ribosomes
• Free ribosomes are located in the cytoplasm of the cell. They are not
attached to any structure, but they may group together with other ribosomes
to form polysomic.
• In the cytoplasm, ribosomes are free floating. They can move all around the
cell.
Bound Ribosomes
• Bound ribosomes are located on the surface of the endoplasmic reticulum
• The endoplasmic reticulum that contains ribosomes is described as the
rough endoplasmic reticulum because of the bumpy surface
• Bound ribosomes can not move to other areas of the cell
• They are attached to the cytosolic side of the endoplasmic reticulum
Golgi Apparatus
Contents/Structure
• Flattened membranous sacs called cisternae
• Two sides of apparatus
• Cis Face - side closest to rough ER
• Trans face – gives rise to vesicles
Functions
• Function in collection, packaging, modification and distribution of
materials synthesized in cell
• Cis side receives materials from the rough ER (proteins, carbs, lipids
ect.)
• Materials are modified as they move through the apparatus before
being packaged at the Trans side
• Vesicles are then created at the Trans side with the material within that
are either taken to various points within the cell or outside the cell
• Also manufactures some macromolecules that when coming out of the
Trans side within vesicles fuse with the plasma membrane
Lysosomes
• Definition: Lysosomes are cellular organelles that contain enzymes
that break down waste materials (individual proteins or entire
microorganisms) and cellular debris. The “stomach of the cell.”
• They are found in animal cells, while their existence in yeasts and
plants is disputed.
• For example, lysosomes digest foreign material and engulfed viruses
and bacteria presenting in phagosomes during the process of
phagocytosis. In addition, lysosomes destroy targeted organelles, such
as mitochondria, and injured cells via autolysis.
• Picture/Diagram:
• **Vesicles: Lysosomes ARE specialized vesicles. Excretory vesicles
(E.V.) excrete waste from the cell (on outer edge).
Mitochondrion
• Definition: Organelles surrounded by two membranes, the inner of
which is folded inwards.
* Remember: Prokaryotic cells do not have mitochondria!*
Function
• The production of Adenosine Triphosphate (ATP)
• “The raw materials used to generate ATP are the foods that we eat, or tissues
within the body that are broken down in a process called catabolism.”
• Programmed Cell Death or APOPTOSIS is another function of the
mitochondria.
• Example:
The main function of the mitochondrion is _________.
a. the production of proteins
b. the “packaging” of proteins
c. to break down waste materials in the cell
d. to produce ATP through cellular respiration
Answer: D
Structures
• The mitochondria is composed
of an inner and outer membrane
• The outer membrane is smooth
while the inner is folded into
cristae (singular, crista)
• Inside the inner membrane there
is a semi-fluid called the matrix
• The matrix is home to ribosomes
and enzymes that assist in the
production of ATP
Chemiosmosis - Definition
• The subsequent movement of ions from an area of higher
concentration to an area of lower concentration through transport
proteins on the selectively-permeable membrane as a result of a proton
gradient that forms across the membrane that is not readily permeable
to ions; the diffusion of hydrogen ions (protons) across the biological
membrane via the ATP synthase
*Chemiosmosis occurs in the mitochondria and plays an important
role in the electron transport chain (ETC)*
The Krebs Cycle - Overview
• The Krebs Cycle takes place between
the cristae of the mitochondrion within
the matrix
• Before the Krebs Cycle can take place,
Glycolysis reduces glucose (a six
carbon chain compound) to pyruvate
(a three carbon chain compound)
• The Pyruvate molecule is then reduced
by the Krebs cycle to Acetyl-CoA (a
two carbon chain)
• It is then merged with Oxaloacetic
Acid (a four carbon chain compound)
to produce a Citric Acid (a six carbon
chain compound)
*To understand the products of this reaction and to
fully understand the concept, please watch
http://www.youtube.com/watch?v=juM2ROSLWfw *
Comparison
Mitochondrion
• Both Plant and Animal Cells
• Contains respiratory enzymes
• Cellular Respiration
• Breaks down simple sugars into
carbon dioxide and release energy
Chloroplast
• Plant Cells
• Contains thylakoid membranes and
pigment molecules
• Photosynthesis
• Uses light to convert carbon, derived
from carbon dioxide into sugar
Both
• Produce energy for the cell to use during its functions
Chloroplasts
• A plastid containing chlorophyll and other pigments, occurring in
plants and algae that carry out photosynthesis
About…
Calvin Cycle Link:
http://www.science.smith.edu/departments/Biology/Bio231/calvin.htmal
A granum is made up of numerous thylakoids stacked like a pile of
coins.
Thylakoids are flattened membrane sacs with the necessary componts
for absorption of light
Stroma contains many enzymes and chemicals needed to complete
photosynthesis
Chloroplast vs. Mitochondria
Chloroplasts
• Chloroplasts have thylakoid
membranes and pigment molecules
• Chloroplasts are part of plant cells
• Chloroplasts use light to convert
carbon into sugar
• Chloroplasts are larger and more
complex
• Only found in plant cells
• Dependent on sunlight as primary
source of food
Mitochondria
• Mitochondria has respiratory enzymes
• Mitochondria are located in the
cytoplasm
• Mitochondria break down simple
sugars into CO2 and release energy
• Mitochondria are found in plant and
animal cells
• Produce ATP
• Self-sustaining, manufacturing own
food
Photosynthesis
• Converts light energy to chemical energy into sugar
• Only needs Carbon Dioxide, water and light energy
• Takes place in plant leaves
• Chlorophyll looks green because it absorbs red and blue light, making
it unavailable to our eyes
• The red and blue are used for photosynthesis
Chlorophyll: Green
Coloration in Leaves
Cell Membrane
a.k.a. Plasma membrane, Cellular
Membrane, Cell Surface Membrane
Cell Membrane composition
Phospholipids
Proteins
Phospholipids
• A Hydrophobic and hydrophilic
head which makes a lipid bilayer.
• Hydrophobic meaning water
hating, this side faces the outside
• Hydrophilic meaning water
loving, this side faces the inside
• The phospholipid heads are
joined together by fatty
acids.
• However, fatty acids aren’t
cemented together, they are
flexible to allow materials to
come in and out of the cell
• These all line up together to
make a lipid bilayer
Functions
• The Cell membranes structure
directly correlates with its function.
• The cell membrane controls entry
and removal of specific molecules
from the cell.
(What they let in and out)
• In addition the cell membrane is
responsible to endocytosis and
exocytosis.
• Endocytosis- process of cellular
absorption: the process by which a
cell membrane folds inward to take
in substances bound to its surface
• Exocytosis- passage of material to
cell surface: the release to a cell
surface of substances such as waste
or secretions through vesicles
Proteins on the Cell Membrane
• The Cell Membrane also has membrane proteins.
The major two types are:
Integral Proteins
Peripheral
Integral Proteins
• Integral or “Integrated” meaning that the protein goes through the
outside of the cell to the inside of the cell.
Peripheral Proteins
• Said to be “anchored” to the surface
• Don’t touch the inside of the cell
Functions of the Proteins made Simple
• These proteins in and on the cell membrane have purpose!
• These functions can be remembered by a simple acronym…..
• Cell communications
• Channels for passive transport
• Hormone binding sites
• Enzymatic activity
• Adhesion to other cells
• Pumps for active transport
These functions in action
• Active and passive transport
• Channel integrated proteins
Active and Passive transport
• Active transport -Use of ATP to pump molecules against the
concentration gradient
• Primary and secondary, some use protein channels to actively move through
the cell membrane
• Passive transport- Movement of molecules with the concentration
gradient
• Diffusion, facilitated diffusion, filtration, osmosis.
The fluid Mosaic Model
• Now we under stand the parts, which will help us understand the
whole.
Cell Wall
Composition
Function
• The cell wall is composed of
cellulose fiber, polysaccharides,
and proteins. When new cells are
formed, their cell wall is thin and
not very rigid. This allows the
cell to grow.
• The function of the cell wall is to
protect the cell and maintain its
shape.
Sources
http://hyperphysics.phy-astr.gsu.edu/hbase/biology/lysosome.html
http://en.wikipedia.org/wiki/Lysosome
http://www.rndsystems.com/molecule_group.aspx?g=711&r=4
http://biology.clc.uc.edu/courses/bio104/photosyn.htm
http://www.thefreedictionary.com/Chloroplasts
http://www.buzzle.com/articles/cell-nucleus-structure-andfunctions.html
http://en.wikipedia.org/wiki/Cell_nucleus
http://www.buzzle.com/articles/where-does-transcription-occur.html