Cells Lecture

7/26/2019 Cells Lecture

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CELL BIOLOGY

CYTOLOGY

The study of the structure, composition and functions of the cell

Cell The basic structural and functional unit of all living things consisting of a mass of

protoplasm with a usually centrally-located nucleus.

Functions of the Cell

1. Basic unit of life

o The cell is the smallest part to which an organism can be reduced that still retains

the characteristics of life.

2. Protection and support

o Cells produce and secrete various molecules that provide protection and support

of the body.Example: bone cells produce mineralized material, making bone a

hard tissue that protects vital organs. !ovement

o !ovements of the body occur because molecules located within specific cells

such as muscle cells.". Communication

o Cells produce and receive chemical and electrical signals that allow them to

communicate with one another.Example: nerve cells communicate with each

other and with muscle cells, causing muscle cells to contract.

#. Cell metabolism and energy release

o The chemical reactions that occur within cells are referred to collectively as cell

metabolism. $nergy released during metabolism is used for cell activities, such as

the synthesis of new molecules, muscle contraction, and heat production, whichhelps maintain body temperature.

%. &nheritance

o $ach cell contains a copy of the genetic information of the individual. 'peciali(ed

cells, sperm cells and oocytes, transmit that genetic information to the ne)t

generation.

History of Cell Biology

1. *obert +ooe

o n $nglishman, coined the term cell and was responsible for the beginnings of

cytology as a discipline in biologyo bserved thin slices of cor with magnifying glass, saw outer boundaries or walls

and called the hollow spaces as /cell0

2. nton an eeuwenhoe

o 3utch, naturalist, discovered bacteria and other microscopic organisms in

rainwater and studied the structure of plant and animal cells.. 4rancesco *edi and a(arro 'pallan(ani

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o 3isproved the theory of spontaneous generation

". *obert Brown

o bserved cells with a central part, the nucleus.

o 3escribed the streaming movement of the cytoplasm as /brownian movement0.

#. 4eli) 3u5ardin

o 6oted that all living things contain a thic 5elly fluid which he calledsarcode%. !atthias 'chleiden and Theodor 'chwann

o &ntroduced the concept that all plants and animals are made up of cells.

7. 8ohannes Purin5e

o Coined the term protoplasm to refer to the living matter of the cell.

9. *udolf irchow

o 4ound out that cells divide to form a new cells. +e concluded that cells come

from pree)isting cells.

Modern Cell Theory

scientific theorywhich describes the properties of cells.

The three tenetsto the cell theory are as described below:

1. ll living organisms are composed of one or more cells

2. The cell is the most basic unit of life.

. ll cells arise from pre-e)isting, living cells.

&n 19;,Theodor 'chwannstates that along with plants, animals are composed of cells or

the product of cells in their structures. This was a ma5or advancement in the field of biologysince little was nown about animal structure up to this point compared to plants. 4rom these

conclusions about plants and animals, two of the three tenets of cell theory were postulated.

Types of Cell

1. ro!"ryotic Cells # cells without a true nucleus

". genetic material is not enclosed in membrane and is not comple)ed with proteins

$. lac a well-defined nucleus and most cell organelles

c. en(ymes for cellular respiration are attached to the plasma membrane

d. ribosomes are free in the cytoplasm but some are attached to messenger *6C


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ii. en(ymes for electron transport system and o)idative phosphorylation are

found in the cristal membrane itself.

d. ribosomes are found in the rough endoplasmic reticulum


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Three 4undamental Parts of the Cell

1. Cell !embrane @ protectively surrounds the cytoplasm

2. Cytoplasm @ the region where the main metabolic life activities tae place

. 6ucleus @ region of the cell where the genetic material is located

1. Cell Me&$r"neCharacteristics of the Cell !embrane

a. &t is a cytoplasmic boundary or limiting membrane condensed into a peripheral film.

b. &t is a selectively permeable or semi-permeable membrane that may or may not allowcertain ions and molecules to enter or leave the cell. ipid-soluble substances can easily

pass through the cell membrane.

4unction of the Cell !embranea. +olds and protects the contents of the cell.

b. 'erves as a limiting membrane that separates the cell from the surroundingenvironment.c. *egulates the internal environment of the cell by regulating incoming and

outgoing materials, accommodates changes in cell volume due to the elasticity

of the cell membrane.d. Transports substances in and out of the cell lie nutrients, gases, hormones

and waste products.

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e. llows transmission of impulses for e)citability thru depolari(ation of charges

along membranes.

f. *esponsible for specificitya. 'ite of antigens @ determines histocompatibility

'tructures ssociated with the Cell !embranea. !icrovilli

structural unit of brush border.

dense, cytoplasmic, slender processes or outpouchings


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c. The cytoplasm provides a medium for the organelles to remain suspended.

d. &t also aids in the movement of the different cellular elements.

e. The cytoplasm acts as a buffer and protects the genetic material of the cell andalso the cellular organelles from damage caused due to movement and collision

with other cells.

Cytoplasmic 'tructure

a. Cytosol Cytosol maes up about 7D of the volume of the cell. &t is composed of

water, salts and organic molecules.

b. rganelles rganelles mean Elittle organsE, that are membrane bound. They are

present inside the cell and perform specific functions that are necessary for

the survival of the cell.

c. Cytoplasmic &nclusions The cytoplasmic inclusions are tiny particles suspended in the cytosol.

rganelles in the Cytoplasm

a. $ndoplasmic *etitculum networ of fine, tube-lie, unit membrane microtunnels that traverse the

cytoplasm between the nuclear envelope and the outer plasma membrane. 4orms a loose networ of canals connecting a comple) set of saccules and

vesicles.

Two Types:

d. *ough or Aranular $*


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ocated between the nucleus and the cell surface and often connected to

the endoplasmic reticulum. &t is involved in modifying, sorting and pacaging macro-molecules for

secretion or for delivery to other organelles.

d. !itochondria or Chondrisomes

'pherical, rod-shaped, cigar or sausage-shaped, somewhat hollowstructures.

3ouble-walled, water-filled membrane consisting of:

o n outer membrane which is smooth, tightly stretched and

completely surrounds the mitochondria

o n inner membrane which is e)tensively invaginated into folds,

forming shelves called cristae which increase the surface for

energy production and en(yme activity. The inner membrane is the

location for energy production and reb?s cycle >nown as the powerhouse of the cell.

o *esponsible for the production of energy in the form of TP


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b. !icrofilament ong, thin, tiny cylindrical fibrils or tubules made up predominantly of

protein tubulin.

&t forms spindle fibers


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Combination of protein, 36 and some *6.

Contains genes which carry the genetic information necessary for replication

and synthesis of protein.". 6ucleolus

3ense spherical ob5ect which is largest in the interphase and disappear in

mitosis. Consists of speciali(ed areas of certain chromosomes called nuclear organi(er,

ribosomal *6 and protein, and is the probable precursor of ribosomes. 4unctions in the construction of ribosomes


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Example: smoke or perfume to distribute throughout a room in which

there are no air currents, or that of a dye throughout a beaker of stillwater.

%. Os&osis

&s the diffusion of water


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o Contains lower concentration of dissolved materials


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+cti-e Tr"nsport

carrier-mediated

process that movessubstances

across the cellmembrane from

regions of lower

concentration tothose of higher

concentration

against a concentration

gradient

ctive transport

reuires energy in the form of TP, and if TP is not available, active transportstops.

1. $ndocytosis

Gptae of material through the cell membrane by the formation of a

membrane-bound sac called a vesicle.

The cell membrane invaginates to form a vesicle containing the material to

be taen into the cell.

a. Phagocytosis @ process by which a cell engulfs or taes in solid

particles that are too large to enter the cell by diffusion.b. Pinocytosis @ process of taing in fluids by cells.

2. $)ocytosis The reverse of endocytosis. &s the process by which a cell e)pels large

molecules such as proteins and polysaccharides.

4actors that affect the 3egree of !embrane Permeability

a. 'i(e of the !olecules @ The bigger the molecule, the slower will it able topermeate through the poreH the smaller the molecule, the faster the permeation.

b. 'i(e of the Pores @ The smaller the poreH the less permeable the membraneH the

bigger the pore, the more permeable it is.c. 'olubility @ lipid and fat solvent substances are capable of dissolving fat

molecules, thus these could pass through the membrane freely.

d. $lectrical charges @ a membrane that is positively charged would repel positivelycharged molecules but would attract negatively charged molecules.

T"$le of Co&p"rison

+cti-e Tr"nsport "ssi-e Tr"nsport

efinition ctive Transport uses TP to pump

molecules A&6'TJGP the

!ovement of molecules 3F6 the

concentration gradient. &t goes from

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concentration gradient. Transport

occurs from a low concentration of

solute to high concentration of solute.

*euires cellular energy.

high to low concentration, in order

to maintain euilibrium in the cells.

3oes not reuire cellular energy.

Types of

Tr"nsport

$ndocytosis, cell membraneJsodium-

potassium pump K e)ocytosis

3iffusion, facilitated diffusion, and

osmosis.

Types of

"rticles

Tr"nsported

proteins, ions, large cells, comple)

sugars.

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http://en.wikipedia.org/wiki/Cell_(biology)http://en.wikipedia.org/wiki/Cell_(biology)http://en.wikipedia.org/wiki/Interphasehttp://en.wikipedia.org/wiki/DNA_replicationhttp://en.wikipedia.org/wiki/DNA_replicationhttp://en.wikipedia.org/wiki/Cell_(biology)http://en.wikipedia.org/wiki/Interphasehttp://en.wikipedia.org/wiki/DNA_replicationhttp://en.wikipedia.org/wiki/DNA_replication


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Interph"se

Before a cell can enter cell division, it needs to tae in nutrients. ll of the preparations

are done during interphase. &nterphase is a series of changes that taes place in a newly

formed cell and its nucleus, before it becomes capable of division again.

&t is also called preparatory phase or intermitosis. Previously it was called resting stage

because there is no apparent activity related to cell division.

Typically interphase lasts for at least ;D of the total time reuired for the cell cycle.

'tages of &nterphase

1. G"p 1 0G1 The first phase within interphase, from the end of the previous ! phase until

the beginning of 36 synthesis

&t is also called the growth phase.

3uring this phase the biosynthetic activities of the cell, which are

considerably slowed down during ! phase, resume at a high rate.

This phase is mared by the use of 2 amino acids to form millions of proteins

and later on en(ymes that are reuired in ' phase, mainly those needed for36 replication.

Cell increases its supply of proteins, increases the number of organelles


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Period when the cell continues to synthesi(e *6 and proteins and increase in

si(e.

The mitotic spindle formed from the cytoinetic fibers start forming and the

cell ensures the number of chromosomes and the organelles present, whichfurther leads the cell cycle from the interphase to the mitotic phase.

MITO'I'

&s the process by which a euaryoticcell separates thechromosomesin its cell

nucleusinto two identical sets in two nuclei.

3uring the process of mitosis the pairs ofchromosomescondense and attach to fibers that

pull thesister chromatidsto opposite sides of the cell.

!itosis and cytoinesis together define the &itotic 0M ph"seof the cell cycle -

the divisionof the mother cell into two daughter cells, genetically identical to each other

and to their parent cell.

This accounts for appro)imately 1D of the cell cycle.

The 2 h"ses of Mitosis

1. roph"se 0the st"ge of prep"r"tion

3uring the prophase the nucleoli in the nucleus disappear.

The chromatin fibers become tightly coiled and condense into chromosomes.

Chromosomes line up in pairs and are 5oined at the centromere.

&n the cytoplasm, the spindle fibers begin to form and are made of

microtubules.

The centrosomes move away from each other, propelled by the lengthening

microtubules, or spindle fibers, between them.

%. Met"ph"se 0st"ge of sep"r"tion The centromeres are at opposite ends of the cell poles.

The chromosomes are lined up at the Imetaphase plateI, an imaginary line

euidistant between the two poles. T

he centromeres of the chromosomes are all aligned with one another.

The chromatids are of each chromosomes are attached to a microtubule which

form the spindle.

(. +n"ph"se 0st"ge of &igr"tion

The paired chromosomes separate.

They move along the microtubules toward opposite poles of the cell.

The poles move farther apart. By the end of anaphase, the two poles of the celleach have a complete set of chromosomes.

2. Teloph"se 0st"ge of nucle"r reconstruction "nd cytoso&e di-ision

The microtubules become even longer, and daughter nuclei begin to form at

the two poles of the cell.

6uclear envelopes are formed, the nucleoli reappear, the chromatin of the

chromosomes uncoils.

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http://en.wikipedia.org/wiki/Eukaryotichttp://en.wikipedia.org/wiki/Chromosomehttp://en.wikipedia.org/wiki/Chromosomehttp://en.wikipedia.org/wiki/Chromosomehttp://en.wikipedia.org/wiki/Cell_nucleushttp://en.wikipedia.org/wiki/Cell_nucleushttp://en.wikipedia.org/wiki/Chromosomeshttp://en.wikipedia.org/wiki/Sister_chromatidshttp://en.wikipedia.org/wiki/Sister_chromatidshttp://en.wikipedia.org/wiki/Cell_divisionhttp://en.wikipedia.org/wiki/Cell_divisionhttp://en.wikipedia.org/wiki/Eukaryotichttp://en.wikipedia.org/wiki/Chromosomehttp://en.wikipedia.org/wiki/Cell_nucleushttp://en.wikipedia.org/wiki/Cell_nucleushttp://en.wikipedia.org/wiki/Chromosomeshttp://en.wikipedia.org/wiki/Sister_chromatidshttp://en.wikipedia.org/wiki/Cell_division


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!itosis is now complete: one nucleus has divided into two genetically

identical nuclei.

Cytoinesis follows and involves the formation of a cleavage furrow, which

pinches the cells in two

MEIO'I'

!eiosis is a type of cell division that reduces the number of chromosomes in the parent

cell by half and produces four gamete cells.

This process is reuired to produce egg and sperm cells for se)ual reproduction.

!eiosis begins with one diploid cell


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h"ses of Meiosis

't"ge I. First Meiotic i-ision 0,eduction i-ision

!eiosis & separates homologous chromosomes, producing two haploid cells


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36 is e)changed betweenhomologous chromosomesin a process

called homologous recombination.

'ubdivided into five stages.

". Leptotene

The diploid chromosomes appear long, thin threads resemblingstrings of beads because of chromomeres.

36 of the nucleus is doubled and each chromosome is

composed of two chromatids.

$. 3ygotene

+omologous chromosomes undergo pairing, synapsis along

their entire length, forming bivalent units.

Chromosomes continue to coil and thicen.

c. "chytene

The paired chromosomes contractH hence each chromosome

becomes shorter and thicer. +omologous chromosomes of each bivalent twist around each

other.

d. iplotene

+omologous chromosomes become visibly double or paired.

$ach bivalent shows four chromatids or tetrad formation.

$)change of chromatid segments or crossing-over forms

chiasma between each homologous pair.

chiasma is the point of contact


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2. Teloph"se I

$ach pole has a haploid number of chromosomes.

nuclear membrane may or may not be reformed around each group

of chromosomes.

't"ge II. 'econd Meiotic i-ision 0E4u"tion"l i-ision

!echanically, the process is similar to mitosis, though its genetic results arefundamentally different. The end result is production of four haploid cells


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Cells Lecture