Cell Structure The “little organs” that perform important functions in the cell are Organelles.
CELL STRUCTURE AND FUNCTIONS · CELL STRUCTURE AND FUNCTIONS Badil Dass ... Understand the...
Transcript of CELL STRUCTURE AND FUNCTIONS · CELL STRUCTURE AND FUNCTIONS Badil Dass ... Understand the...
CELL STRUCTURE AND FUNCTIONS
Badil Dass
Karachi King’s College of Nursing
�At the end of session students will be able to
�Understand the structure of cell.
�Identify cell organelles and their functions.
�Explain DNA, Genes & Chromosomes.
LEARNING OBJECTIVES
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�Explain DNA, Genes & Chromosomes.
�Functional unit
�Unicellular
�Cellular level
�Tissue level
CELL
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�Unicellular
�Multicellular
�Tissue level
�Organ level
�System level
Cellular level
CELLULAR LEVEL
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Cellular level
TISSUE LEVEL
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ORGAN LEVEL
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SYSTEM LEVEL
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� Controls cellular traffic
� Proteins that span
PLASMA MEMBRANE
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through the membrane and allow passage of materials
� Phospholipid bi-layer.
� Powerhouse of the cell
� Double-layered outer membrane with inner folds calledcristae
� Energy-producing
MITOCHONDRIA
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� Energy-producing chemical reactions take place on cristae
� Recycles and decomposes proteins, fats, and carbohydrates, and forms urea.
� Other cellular activities� Apoptosis. � Production of cholesterol and
heme
� Mitochondrial DNA contains
MITOCHONDRIA
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� Mitochondrial DNA contains 37 genes
� Thirteen of these genes for enzymes involved in oxidative phosphorylation.
� Remaining genes for � tRNAs� rRNAs
�Membrane-bound sacs for storage, digestion, and waste removal
VACUOLES
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removal�Contains water
solution�Contractile vacuoles
for water removal (in unicellular organisms)
�Tubular network fused to nuclear membrane
�Stores, separates,
ENDOPLASMIC RETICULUM
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�Stores, separates, and serves as cell's transport system
�Smooth type
�Rough type
�Protein factories
�Composes 25% of cell's mass
RIBOSOMES
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�Composes 25% of cell's mass
�Stationary type: embedded in rough endoplasmic reticulum
�Mobile type: injects proteins directly into cytoplasm
�A membrane structure found near nucleus
�Composed of numerous layers
GOLGI APPARATUS
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numerous layers forming a sac
�Protein 'packaging plant‘ �process according to
specific needs and then send their destinations
� Digestive 'plant' for
proteins, l ipids, and
carbohydrates
� Transports undigested
LYSOSOME
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� Transports undigested
material to cell membrane
for removal
� Vary in shape depending on
process being carried out
� Cell breaks down if
lysosome explodes
�Composed of microtubules
�Supports cell and provides shape
CYTOSKELETON
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provides shape
�Aids movement of materials in and out of cells
� Paired cylindrical organelles near nucleus
� Composed of nine tubes, each with three tubules
� Involved in cellular division
� Lie at right angles to each other
CENTRIOLES
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� Spherical shape
� Visible when cell is not dividing
� Contains RNA for protein manufacture
NUCLEOLUS
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� Surrounds nucleus
� Composed of two layers
� Numerous openings for nuclear traffic
NUCLEAR MEMBRANE
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� Usually in the form of chromatin
� Contains genetic information
� Composed of DNA
� Thicken for cellular division
� Set number per species (i.e. 23 pairs for human)
CHROMOSOMES
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� Set number per species (i.e. 23 pairs for human)
DNA
�DNA, or deoxyribonucleic
acid, is the hereditary material
in humans and almost all other
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in humans and almost all other
organisms.
�Nearly every cell in a person’s
body has the same DNA.
DNA
�Most DNA is located in the
cell nucleus (where it is
called nuclear DNA), but a
small amount of DNA can
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small amount of DNA can
also be found in the
mitochondria (where it is
called mitochondrial
DNA or mtDNA).
� The information in DNA is stored as a code made up of four chemical bases: adenine (A), guanine (G), cytosine (C), and thymine (T).
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� Human DNA consists of about 3 billion bases, and more than 99% of those bases are the same in all people.
� DNA bases pair up with each other, A with T and C with G, to
form units called base pairs.
CONTI……..
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� Each base is also attached to a sugar molecule and a phosphate
molecule.
� Together, a base, sugar, and phosphate are called a nucleotide.
� Nucleotides are arranged in two long strands that form a
spiral called a double helix.
CONTI…….
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� The structure of the double helix is somewhat like a ladder,
with the base pairs forming the ladder’s rungs and the sugar
and phosphate molecules forming the vertical side pieces of
the ladder.
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� DNA can replicate, or make copies of itself.
� Each strand of DNA in the double helix can serve as a pattern
for duplicating the sequence of bases.
CONTI……
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� This is critical when cells divide because each new cell needs
to have an exact copy of the DNA present in the old cell.
�Basic physical and functional unit of heredity.
�Segments of DNA located on chromosomes.
GENES
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�Genes act as instructions to make molecules called proteins.
� In humans, genes vary in size from a few hundred DNA bases to more than 2 million bases.
CHROMOSOME
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Genes are made up of DNA. Each chromosome contains many genes.
� Every person has two copies of each gene, one inherited from each parent.
� Most genes are the same in all people, but a small number of genes (less than 1% of the total) are slightly
CONTI…….
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number of genes (less than 1% of the total) are slightly different between people.
� Alleles are forms of the same gene with small differences in their sequence of DNA bases. These small differences contribute to each person’s unique physical features.
�DNA molecule is packaged into thread-like structures called chromosomes.
�Each chromosome is made up of DNA tightly
CHROMOSOME
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�Each chromosome is made up of DNA tightly coiled many times around proteins called histones that support its structure.
�Each chromosome has a constriction point called the centromere, which divides the chromosome into two sections, or “arms.”
�The short arm of the chromosome is labelled the “p
CONTI………
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�The short arm of the chromosome is labelled the “p arm.”
�The long arm of the chromosome is labelled the “q arm.”
�The location of the centromere on each chromosome gives the chromosome its characteristic shape, and can be used to help describe the location of specific genes.
35DNA and histone proteins are packaged into structures called chromosomes.
�Chromosomes are not visible in the cell’s nucleus—not even under a microscope—when the cell is not dividing.
�DNA that makes up chromosomes becomes more tightly
CONTI…….
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�DNA that makes up chromosomes becomes more tightly packed during cell division and is then visible under a microscope.
�Most of what researchers know about chromosomes was learned by observing chromosomes during cell division.
� Euchromatin, which consists of DNA that is active, e.g., being
expressed as protein.
� Heterochromatin, which consists of mostly inactive DNA. It
CONTI……..
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� Heterochromatin, which consists of mostly inactive DNA. It
seems to serve structural purposes during the chromosomal
stages. Heterochromatin can be further distinguished into two
types:
� Constitutive heterochromatin, which is never expressed. It is located
around the centromere.
� Facultative heterochromatin, which is sometimes expressed.
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� In humans, each cell normally contains 23 pairs of
chromosomes, for a total of 46.
� Twenty -two of these pairs, called autosomes.
CONTI……
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� Twenty -two of these pairs, called autosomes.
� The 23rd pair, the sex chromosomes, dif fer between males
and females.
� Females have two copies of the X chromosome, while males
have one X and one Y chromosome.
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The 22 autosomes are numbered by size. The other two chromosomes, X and Y,
are the sex chromosomes. This picture of the human chromosomes lined up in
pairs is called a karyotype.
�Cell-to-cell communication is absolutely
essential for multicellular organisms and is
also important for many unicellular organisms.
CELL COMMUNICATION
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also important for many unicellular organisms.
�Cells must communicate to coordinate their
activities.
�Direct contact
�Paracrine signaling
�Endocrine signaling
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�Endocrine signaling
�Synaptic signaling
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� Cells touch each other and signal molecules
travel through special connections called
communicating junctions
DIRECT CONTACT
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� Communicating junctions link the cytoplasms of 2
cells together, permitting the controlled passage
of small molecules or ions between them.
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� The cells of a organism communicate with each other by releasing signal molecules that bind to receptor proteins located either on or inside of target cells.
� Three stages of cell signaling:
� Reception - each target cell has receptors that detect a specific signal molecule and binds to it
CELL SIGNALING
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a specific signal molecule and binds to it
� Transduction – binding of the signal molecule changes the receptor protein in some way that initiates transduction or conversion of the signal to a form that can bring about a specific cellular response
� Response – transduced signal triggers a specific cellular response, any cell activity
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�A signal molecule binds to a receptor protein, causing it to change shape
�The binding between signal molecule (ligand) and receptor is highly specific
RECEPTION
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�A conformational change in a receptor
� Is often the initial transduction of the signal
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� Intracellular receptors
� Some signal molecules that are small or hydrophobic can pass through the plasma membrane and bind to receptors located inside the cell
� Intracellular receptors are cytoplasmic or nuclear proteins
RECEPTORS
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� Cell surface receptors. - Signal molecules that cannot pass through the plasma membrane bind to receptors located on the surface of the membrane
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�Some enzymatic receptors and most G-protein-linked receptors relay their message into the cell by activating other molecules or ions inside the cell.
SECOND MESSENGERS
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�These molecules and ions, called second messengers, transmit the message within the cell. The 2 most common second messengers are cAMP and Ca++
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� Transduction usually involves multiple steps
� Multistep pathways
� Can amplify a signal
� Provide more opportunities for coordination and
SIGNAL TRANSDUCTION PATHWAYS
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� Provide more opportunities for coordination and regulation
� The molecules that relay a signal from receptor to response are mostly proteins
� The receptor activates another protein, which activates another, and so on, until the protein producing the response is activated
SIGNAL TRANSDUCTION PATHWAYS
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� At each step, the signal is transduced into a different form, usually a conformational change
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