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THE CELL
It is the basic unit that contains the
fundamental molecules of life.
CELLS
• They were discovered after the invention of the microscope, by a British
naturalist called Robert Hook. He was analyzing a very thin layer of cork
tissue under a microscope when he found them out. He called them cells
because they seemed as cells in a monastery.
• It is the basic, smallest and simplest unit of all living things.
• All organisms are made of one or more cells.
• All cells came from pre-existing cells
• In multicellular organisms, cells can work independently or work together
in a coordinated way.
TYPES OF CELLS
They can vary according to the shape (that changes
relating to the function or if they are animal or plant cells), to
the size (though it is usually between 1-100 micrometers) or
to their complexity. There are two types according to their
complexity:
• PROKARYOTIC: bacteria and cyanobacteria have prokaryotic
cells. Prokaryotic cells only have a cell membrane, a cell wall,
ribosomes and genetic material, which flows freely in the
cytoplasm.
• EUKARYOTIC: protists, fungi, plants and animals have
eukaryotic cells. They have several advantages over
prokaryotic cells. There are two types: animal and plant cells.
LEVELS OF BIOLOGICAL
ORGANISATION
CELL FUNCTIONS
• Interaction: cells can communicate with the
environment by adapting to the changes around it
and maintaining the activities it needs to live. It
consists on to actions: receiving information to
detect environmental changes and responding
appropriately to them.
CELL FUNCTIONS
• Nutrition: cells take different molecules from the
environment and transform them into energy in
order to make it function or to renew its cellular
structure. These transformation take place in a
process called metabolism. It consists on all the
chemical reactions that take place inside the cell to
produce ATP. Waste products are produced and
usually expelled out of the cell.
METABOLISM
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Blosynthesis
Contraction
Chemical activation
Importing metabolites
Active Transport: Na-K Pump
Cytoplasmic transport
Flagellar Movements
Cell crawling
Heat production
CELL FUNCTIONS
• Reproduction: it consists on the formation of two
new cells from the existing ones. It is used: for singlecelled organisms, to create new individuals, and for
multicellular ones to replace dead cells and to
increase the number of cells for an organism that is
growing. Genetic material of the parent consists on
their biological characteristics, which are passed to
daughter cells, and thus, they are identical to the
parent cell.
THE CELL LIFE CYCLE
• In prokaryotes, cell division
can occur at any moment,
but eukaryotic cells
duplicate their DNA exactly
once during a discrete
period between cell
divisions.
THE CELL LIFE CYCLE
• Interphase is the period of time until the cell receives a signal that makes
it replace itself. In G0 (gap 0) , no more synthesis occurs. Some cells such
us neurons or muscles cells never leave this stage. In G1 (gap one) RNA
and proteins synthesise. In S (synthesis), DNA and chromosomes
replicate, protein synthesis, chromosomes duplicate and centromeres
duplicate. In G2 (gap 2), centrioles grow, tubulin for spindle apparatus is
synthesised, and energy is stored .Mitosis is the process in which the
nucleus is divided
• S phase
MITOSIS
• Cell division is a process that cells undergo to
repair or grow body tissues. Mitosis is a
processs of cell division in which a parent cell
produces two daughter cells with identical
genetic information. All the cells undergo
mitosis except gamates (that are produced
through meiosis), neurons and muscle cells.
Before mitosis occurs, genetic information has
to be replicated (S phase).
MITOSIS
• PROPHASE: centrioles move to each of the sides of
the cells and start building up a mitotic spindle made
up of microtubules (tubulin protein). The nucleolus
and the nuclear membrane disappear. Genetic
material thickens and shortens to make
chromosomes, that are made up of two chromatids
linked by a centrosome.
MITOSIS
• METAPHASE: The chromosomes move to the
equatorial plane (centre of the cell) and join to
the spindle fibers in the centrosomes. Tubilin
shortens and depolymerizes it.
MITOSIS
• ANAPHASE: Spindle fibers break in the
centromeres and pull apart chromatids (half
of a chromosome) to the opposite sides of a
cell.
MITOSIS
• TELOPHASE: when chromatids have reached the
centrioles, spindle fiibers disappear. A nuclear
membrane surrounds the chromosomes (the
chromatids join), forming two daughter nuclei.
Chromosomes start to transform into chromatin (the
substance in which DNA is found during interphase).
The nucleolus reappears too.
CYTOKINESIS
• The cytoplasm divides.
• In animal cells, cytoplasm stretches, thinnens and separates.
• In plant cells, a wall is built in the middle of the cell
(cellplate), which divides the cytoplams in half.
MEIOSIS
• It is the process when a
diploid/somatic cells with a
complete set of
chromosomes (2n) divides
into four haploid cells or
gamates (n).
• Its purpose is to create
gamates with different
genetic material creating
variability of species to
avoid diseases .
• It consists on two
consecutive cell divisions:
MEIOSIS
• FIRST DIVISION: reduction division. The differences between a normal
mitosis are:
• PROPHASE: chromosomes appear in pairs. These pair of chromosomes are
called homologous, and they have the same structure and position. They
undergo a process called crossing over. In this process, chromosomes
exchange genetic information. However, only the ones that are in the
centre are going to exchange particular segments, because bonds are
easilier to change. The parts that are farther from the centromere are
more likely to cross-over.
The physical point where it happpens is called chiasm
• METAPHASE: entire chromosomes (crossedover chromosomes) go to the equatorial plane
and are linked to the mitotic spindle.
• ANAPHASE: chromosomes are pulled to the
sides of the cell.
• TELOPHASE: two daughter hapolid nuclei with
n chromosomes are formed.
MEIOSIS
• SECOND DIVISION: Before the second mitosis there’s no duplication of
DNA. It is as a normal mitosis. The result is four haploid cells with unique
genetic combination.
Production of gamates is
random because of:
• Independent assortment
(2^23 possibilities to get
through independent
assortment). Crossing
over
• Random fertilization
(millions of sperm are
ejaculated and you were
the one to success).
CELL ORGANELLES
• They are structures consisting on a space usually enclosed by
a membrane (or two) that perform specilised functions.
ORGANELLES
• CYTOSKELETON:
microscopic network of
tubules that give cells
their shape and is in
charge of the cell’s
movility and movement
of the cell’s organelles.
It is made up of
microtubules,
microfilaments and
intermediate fibers.
ORGANELLE
•
CELL MEMBRANE: it is a flexible bilayer membrane made up of phospholipids.
These phospholipids have a negative charged heads that are hydrophilic, and a
non-polar tails that are hydrophobic. It also contains proteins, that are anchores
to the cell membrane thanks to hydrophilic regions. Material inside the membrane
is continuously moving around and floating. Its functions are to keep water on
either side of the cell as well as toxic substances out of the cell; and proteins can
act as receptors can act as receptors, enzymes, surface antigens, transporters and
channels that allow to pass specific molecules, such as ions, nutrients or wastes. As
lipid’s heads are charged, the only substances that can pass are the uncharged
ones. However, oxygen, hydrogen and carbon dioxide don’t need to be charged
because they are small and fat-soluble substances that can enter the membrane
by diffusion. Despite, negative charged heads repel large, water-soluble molecules,
such as sugar, and electrically charged ions, such as calcium. The protein channels
let big molecules to pass in or out of the cell, though. When the cell is immersed
in a aqueous solution the tails embed deeply and leave the hydrophilic heads
exposed, leaving the cell insulated from most substances, plus this is a handy
membrane because it can automatically fix itself when it’s torn.
ORGANELLES
• CENTROSOME: they are
structures in charge of creating
microtubules and take part in cell
division. Plant’s centrosomes are
simplier than animal’s
centrosomes because they are
not made up of two centrioles as
they are.
• During animal cell division,
centrioles replicate and the
centrosome divides, resulting of
two centrosomes with two pair
of centrioles each. The
centrosomes move to the
opposite side of the nucleus and,
from each one, microtubules
grow into a “spindle” that
separates the chromosomes.
ORGANELLES
• ROUGH AND SMOOTH
ENDOPLASMIC
RETICULUM: they are a
complicated network of
tubes (pipes) and vesicles
(cisterns) surrounded by a
membrane similar to the
plasmatic membrane. It
makes and transports
lipids (smooth) and
proteins (rough).
ORGANELLES
• GOLGI APPARATUS: it is an organelle made up of
vesicles and flattened sacs called cisternae surrounded
by a single membrane. Its function is to take
substances or macromolecules from the endoplasmic
reticulumand send them through vesicles throughout
the cell. Vesicles that transport substances to the
outside of the cell are called secretion vesicles.
Substances can go to lysosomes, to vacuoles or for
secretion. The stack of large vesiclesis surrounded by
numerous smaller vesicles containing the packaged
macromolecules.
• It is also in charge of builing up lysosomes and of
digesting nutrient
ORGANELLES
• LYSOSOMES: tiny
vesicles (small bubbles
enclosed by a
membrane) that
contain enzymes that
can digest large
molecules or bacteria.
Uncontrolled release of
lysosome content can
cause a cell to die.
ORGANNELES
O
•
CHLOROPLAST: they have two
smooth membranes. In their
interior, there are disc-shaped sacs
called thylakoids, who are in charge
of taking the electrons released
during photosynthesis. It also has
chlorophyll inside, that makes
plants green and is sensitive to
light. Solar radiation is transformed
into chemical energy and inorganic
substances like carbon dioxide are
transformed into organic
substances like glucose.
•
H
H
H2O bonds break.
6CO2 + 2protons= C6H12O6
C6H12O6 + O2= ATP
ORGANELLES
• VACUOLE: they are structures
that store various substances
(nutrients, waste substances)
and are enclosed by a
membrane. In plant cells, they
are bigger and more numerous
than in animal cells, and they
can occupy even th 80% of the
total space of the plant cell.
They play roles in intracellular
digestion and can act as
lysosomes in animal cells. In
plant cells, they also regulate
the pressure of the cell.
ORGANELLES
•
NUCLEUS: Nucleus: is a membraneenclosed organelle found in
eukaryotic cells.. It contains most of
the cell's genetic material l, made up
of DNA molecules. These contain the
information necessary to control
cellular activity (plus cell growth and
reproduction), give the cell its
specific characteristics ¡and encode
proteins (in nuclei acid). It has pores
that open or close if any material (like
ribosomes, created in the nucleolus)
wants to get out. The nucleus is filled
with nucleoplasm and is surrounded
by an internal and external
membrane. In its interior, it contains
the nucleolus and the DNA in form of
chromatin (DNA in the interphase).
ORGANELLES
• NUCLEOLUS: it is a spherical
structure with no membrane
which is involved in the
synthesis of ribosomes. To get
outside the nucleus,
ribosomes have o break in two
halves. Then, they go to the
rough endoplasmic reticulum.
• RIBOSOMES: they are found in
the cytoplasm or attached to
the rough endoplasmic
reticulum. They have no
membrane, and are
responsible for the
synthesising of proteins. They
have two subunits with three
nucleoitides each one.
• They are also in charge of the
transference of RNA (tRNA).
mRNA codifies two proteins
that are built in the ribosomes.
RIBOSOME
ORGANELLES
•
•
•
MITOCHONDRIA: It appears both in
animal and plant cells. It is a double
membrane organelle. The external
membrane is smooth while the
other is folded inside in multiple
folds called cristae. In its interior, it
contains mitochondrial matrix, a
gel-like substance with ribosomes,
DNA and enzymes.
It produces ATP: from the rupture
of glucouse into two piruvic acids
(a process called glycosis that
happens in the matrix) plus oxygen
we have carbon dioxide , water and
ATP. This process is called cellular
respiration or aerobic respiration.
Glucouse
C6H12O6+ 6 O2 = 6 CO2 +6 H2O+ ENERGY.
THE BRAKE OF THE CARBON BONDS FROM THE PYRUVIC ACIDS CREATE ENERGY THAT
IT’S STURED IN FORM OF ATP (ADENINE TRIPHOSPHATE) A EXTREMELY UNSTABLE
COMPOUND.
2 pyruvic acids
ORGANELLES
Cells that move:
Some eukaryotic cells can move
using cilia and flagella or using
the changes in the viscosity
(resistance to flow of a liquid)
of its cytoplasm to produce
temporary proyections called
pseudopods.
Cilia and flagella are organelles
formed from the same protein
fibers of the cytoskeleton
(tubulin). They are located
outside the cell. Its movement
is controlled by the centriole.
GENETICS
VOCABULARY
• Gene: segments of DNA that codify particular proteins.
They transmit genetic information
• Allele: any of two or more variants of a gene that have the
same relative position on homologous chromosomes and
are responsible for alternative characteristics, such as
smooth or wrinkled seeds in peas .
• Genotype: All the genes that make up an organism
• Phenotype: particular genes that are “active”. They become
active according to the internal and external environment.
They are observable traits in an individual.
• Phenotype: The observable characteristics of a genotype of
an organism.
GENES
• A gene can have two variants
(because the genetic material has
two strands), that are called
alleles. The individual can have
two alleles for each trait: in
homozygous individuals both
alleles are the same, and in
heterozygous individuals alleles
are different. When the alleles
are different, one allele can be
dominant. This means that, if the
allele N is dominant, the trait of
Nn will be the same as if it was
NN. The other allele is called
recessive. There is a codominance when there is no
dominant allele, so the traits are
mixed.
GREGOR MENDEL
• Mendel was the first person to
study transmission of
biological traits. He was an
Austrian monk,
mathemathisian and gardener
that lived during the 19th
century. He made an
experiment using different
species of peas and cultivated
them until they were purebred
(homozygous). Then, he
crossed. His discoveries form
the basis of modern genetics,
and can be divided into three
principles.
MENDEL’S EXPERIMENT
MENDEL’S LAWS
• Principle of uniformity:
When two homozygous individuals are crossed,
their offspring (F1) will have identical
phenotypes and genotypes. If there is
dominance between the alleles, the
phenotype of the offspring is the same as
one of the parents. If there is co-dominance
their phenotype is an intermediate between
the phenotype of both parents.
Example: We have the Parents, PP and pp. The
particles (P or p) divide in meiosis and
separate: P-P p-p gamates. Then they
combine :
There are four combinations Pp- Pp - Pp - Pp. The
First Generation will have the same
phenotypes and genotypes.
If one allele is dominant (let’s suppose it is P like
in the fourth picture), the offspring will have
identical phenotypes as its parent PP.
MENDEL’S LAWS
•
Principle of segregation: it is the first
law of inheritance. When two
heterozygous individuals are crossed
(F1) their offsprings will have different
genotypes and phenotypes composed
of the combination of the different
gamates.
Example: We take the previous example.
We have the First Generation: Pp- Pp
- Pp - Pp .
Then, the particles separate in meiosis
creating gametes. They are: P-p P-p
Now we combine it with itself, producing:
PP- Pp- Pp- pp. As we can see, the
Second Generation has a 25% of
possibilities of being homozygous PP,
25% of possibilities of beign
homozygous pp and 50% of
possibilities of beign heterozygous Pp.
MENDEL’S LAWS
• Principle of independent
assortment: It is Mendel’s
second law of
inheritance. When two
individuals with two or
more traits are crossed,
each trait will transmit
independently.
• This Mendel law isn’t
universal, it only applies
for non-linked traits.
OSMOSIS
OSMOSIS
• It is a type of diffusion.
Osmosis is the passage of
water or any other solvent
through a semipermeable
membrane. The
semipermeable membrane
allows the movement of water
but doesn’ allow the
movement of the solute
molecules. The water flows
from an area of high water
concentration to an area of
low water concentration.
Sugar molecules can’t cross
that semipermeable
membrane.
Rosalía Martín Muñoz
Biology, 4th A