Download - CELL STRUCTURE AND FUNCTIONS · CELL STRUCTURE AND FUNCTIONS Badil Dass ... Understand the structure of cell. Identify cell organelles and their functions. Explain DNA, Genes & Chromosomes.

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.

� 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.

� 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

� 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.

� 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

�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

� 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

�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++

� 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