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...
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CELL STRUCTURE AND FUNCTIONS
Badil Dass
Karachi King’s College of Nursing
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�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.
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�Functional unit
�Unicellular
�Cellular level
�Tissue level
CELL
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�Unicellular
�Multicellular
�Tissue level
�Organ level
�System level
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Cellular level
CELLULAR LEVEL
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Cellular level
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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.
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� 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.
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� Other cellular activities� Apoptosis. � Production of cholesterol and
heme
� Mitochondrial DNA contains
MITOCHONDRIA
12
� Mitochondrial DNA contains 37 genes
� Thirteen of these genes for enzymes involved in oxidative phosphorylation.
� Remaining genes for � tRNAs� rRNAs
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�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)
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�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
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�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
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�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
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� 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
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�Composed of microtubules
�Supports cell and provides shape
CYTOSKELETON
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provides shape
�Aids movement of materials in and out of cells
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� 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)
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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.
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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).
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� 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.
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� 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.
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� 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……
29
� This is critical when cells divide because each new cell needs
to have an exact copy of the DNA present in the old cell.
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�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.
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CHROMOSOME
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Genes are made up of DNA. Each chromosome contains many genes.
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� 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.
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�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.
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�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………
34
�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.
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35DNA and histone proteins are packaged into structures called chromosomes.
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�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.
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� 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.
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�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.
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�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
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� Provide more opportunities for coordination and regulation
� The molecules that relay a signal from receptor to response are mostly proteins
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� The receptor activates another protein, which activates another, and so on, until the protein producing the response is activated
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� At each step, the signal is transduced into a different form, usually a conformational change
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