Cytology:

Cells & mitosis

Introduction

• Cells are the structural “building blocks” of

all plants and animals.

• Cells are produced by the division of pre-

existing cells.

• Cells are the smallest structural units that

perform all vital functions.

Introduction

• Cells fall into two categories:

• Sex cells (germ cells or reproductive

cells), which are the sperm in males and

oocyte in females.

• Somatic cells are all of the other cells in

the body that are not sex cells.

Cytology- The study of cells

light microscopy

(respiratory tract)

LM 400 TEM 2400 SEM 14,000

Transmission electron microscopy

(intestinal tract)

Scanning electron

microscopy

(respiratory tract)

Cells are diverse in structure & function

Smooth

muscle

cell

Blood

cells

Bone

cell

Oocyte Sperm

Neuron in

brain

Fat cell

Cells lining

intestinal tract

Anatomy of a Typical

Cell Microvilli

Secretory

vesicles

Cytosol

Lysosome

Centrosome Centriole

Chromatin

Nucleoplasm

Nucleolus

Nuclear envelope

surrounding nucleus

Cytoskeleton

Plasmalemma

Golgi apparatus

Mitochondrion

Peroxisome

Nuclear pores

Smooth

endoplasmic

reticulum Rough

endoplasmic

reticulum Fixed ribosomes

Free ribosomes

The Study of Cell Structures

CYTOPLASM

CYTOSOL

PLASMALEMMA

ORGANELLES

NONMEMBRANOUS ORGANELLES

MEMBRANOUS ORGANELLES

THE CELL

• Cytoskeleton

• Microvilli

• Centrioles

• Cilia

• Flagella

• Ribosomes

• Mitochondria

• Nucleus

• Endoplasmic

reticulum

• Golgi apparatus

• Lysosomes

• Peroxisomes

Cell Anatomy

Cell Anatomy

The Plasma membrane

Phospholipid bilayer

• polar heads = hydrophillic ( face inside and outside of the cell);

• greasy lipid parts = hydrophobic (found in the middle of the membrane layer)

• Proteins and cholesterol are also found embedded in the membrane

• Four major functions of the cell membrane can be described:

– Physical Isolation

– Regulation of exchange with the environment

– Sensitivity

– Structural support

Glycolipids

of glycocalyx Phospholipid

bilayer

Integral protein

with channel

Hydrophobic

tails

Gated

channel

Cholesterol

Peripheral

proteins Hydrophilic

heads

Cytoskeleton

(Microfilaments) 2 nm CYTOPLASM

The plasmalemma

The phospholipid bilayer

Hydrophobic

tails

Hydrophilic

heads

Cholesterol

Integral

glycoproteins

EXTRACELLULAR FLUID

The Plasma membrane

The Plasma membrane

Glycolipids

of glycocalyx Phospholipid

bilayer

Integral protein

with channel

Hydrophobic

tails

Gated

channel

Cholesterol

Peripheral

proteins Hydrophilic

heads

Cytoskeleton

(Microfilaments) 2 nm CYTOPLASM

Integral

glycoproteins

EXTRACELLULAR FLUID

Cholesterol serves to stabilize the membrane structure & maintain its fluidity;

Carbohydrates found on outside surface of cell ex. receptors

The Plasma membrane

The phospholipid bilayer

Hydrophobic

tails

Hydrophilic

heads

Cholesterol

Movement across

Membrane

Plasmalemma Channel

protein

CYTOPLASM

EXTRACELLULAR

FLUID

Lipids, lipid-soluble molecules, and soluble gases (O2 and CO2) can diffuse across the lipid bilayer of the plasmalemma.

Water, small water- soluble molecules, and ions diffuse through membrane channels.

Large molecules that cannot fit through the membrane channels and cannot diffuse through the membrane lipids can only cross the plasmalemma when transported by a carrier mechanism.

Cytoplasm: Cytosol and

Organelles • The cytoplasm is the general term for the

material inside the cell.

• The cytosol is the intracellular fluid.

– high in potassium ions.

– contains high concentrations of proteins.

• Organelles are structures within the cytoplasm each with a specific structure and function. – Non-membranous organelles

– membranous organelles

Non-Membranous organelles

• Cytoskeleton

• Microvilli

• Centrosomes

• Cilia

• Ribomes

The Cytoskeleton

A SEM image of the microfilaments

and microvilli of an intestinal cell

Microtubules in a living cell, as

seen after special fluorescent

labeling

LM 3200

SEM 30,000

Microvilli

Microfilaments

Plasmalemma

Terminal web

Mitochondrion

Intermediate

filaments

Endoplasmic

reticulum

Microtubule

Secretory

vesicle

Microfilaments can

produce movement of a

portion of a cell

Ex. Microvilli increases

surface area for

absorption

Intermediate filaments

provide strength & stability

Microtubules- hollow tubes

that transport organelles

(think roads)

Centrioles and Cilia made by microtubules

Microtubules

Basal body

Plasmalemma

Microtubules

Power stroke Return stroke

TEM 240,000

Centrioles

direct the movement of

chromosomes

in cell division;

a pair = centrosomes

Cilia usually

move mucus

along cell

surface

Ribosomes

Nucleus Free ribosomes

Endoplasmic

reticulum with

attached fixed

ribosomes

Small ribosomal

subunit

Large ribosomal

subunit

TEM 73,600

Both free and fixed ribosomes can

be seen in the cytoplasm of this cell.

An individual ribosome,

consisting of small and

large subunits

Ribosomes: composed of RNA + protein

Read the genetic instructions and build proteins

Can be on membranes (rough endoplasmic reticulum) or away

from membranes (free ribosomes)

Membranous organelles

• Mitochondria

• Nucleus

• Endoplasmic reticulum

• Golgi apparatus

• Lysosome

• Peroxisome

Mitochondria = cell power house (ATP)

Inner membrane

Organic molecules

and O2

CO2

ATP

Matrix Cristae Enzymes

Outer

membrane

TEM 61,776

Cytoplasm

of cell Cristae Matrix

Mitochondria are double-membraned organelles that

control their own maintenance, growth & reproduction;

generate 95% of ATP required by the cell through the

breakdown of organic molecules

The Nucleus = control center

Perinuclear

space

Nucleoplasm

Chromatin

Nucleolus

Nuclear envelope

Nuclear pores

TEM showing important nuclear structures

TEM 4828 The Nucleus is the control center of the cell

-Control of metabolism

-Storage and processing of genetic info

-Control of protein synthesis Parts:

-Nucleolus

-Nuclear envelope

-Nuclear pores

Chromosome vs. Chromatin

Nucleus of nondividing cell

Chromatin in nucleus

Dividing cell Visible chromosome

Supercoiled

region

Nucleosome

Histones DNA double

helix

In cells that are not

dividing, the

nucleosomes are loosely

coiled, forming a tangle

of fine filaments known

as chromatin.

Chromosomes (in

dividing cells): condense

their DNA to protect it

during Division; tightly

coiled

Chromatin (in non-diving cells) : the

form when the DNA is not in chromosomes

(DNA is being used); loosely coiled

Endoplasmic Reticulum (ER)

• The endoplasmic reticulum (ER) has four major functions:

– Synthesis of all classes of macromolecules

– Storage of the manufactured molecules

– Transport of substances from one area of the cell to another

– Enzymes in the lumen of the ER provide detoxification.

• Rough and Smooth ER

The Endoplasmic Reticulum: Rough and Smooth ER

Ribosomes

Cisternae

Rough endoplasmic

reticulum with

fixed (attached)

ribosomes

Free

ribosomes

Smooth

endoplasmic

reticulum

Endoplasmic

Reticulum

TEM 11,000

Rough ER- synthesizes

proteins and phospholipids;

transport vesicles deliver proteins

to the golgi apparatus

Smooth ER- synthesizes

other lipids; stores calcium;

detoxification

• Golgi apparatus are stacks of flattened membranes containing chambers

Golgi apparatus

Three main functions:

1. Synthesis and packaging of

secretions

2. Packaging of special enzymes

for use in the cytosol

3. Renewal or modification of the

cell membrane

Golgi apparatus

1. Proteins to be released from the cell are sorted into secretory vesicles, and released from the plasma membrane (exocytosis).

2. Phospholipids are added to renew the cell membrane when vesicles fuse.

Lysosome

• Lysosomes are vesicles filled with digestive

enzymes.

• Three main functions:

1. Lysosomes fuse with and recycle damaged

organelles.

2. Lysosomes fuse with phagosomes to digest

solid materials (damaged organelles or of

pathogens).

3. Lysosomes sometimes rupture resulting in

autolysis.

Figure 2.17 Lysosomal Functions

Waste products and debris are then ejected from the

cell when the vesicle fuses with the plasma membrane.

Endocytosis

Extracellular

solid or fluid

As digestion

occurs, nutrients

are reabsorbed for

recycling.

Primary

lysosomes

contain

inactive

enzymes.

As the materials

or pathogens are

broken down,

nutrients are

absorbed.

Golgi

apparatus

Function 1: A primary

lysosome may fuse with

the membrane of another

organelle, such as a

mitochondrion, forming a

secondary lysosome.

Function 2: A secondary

lysosome may also form

when a primary lysosome

fuses with a vesicle

containing fluid or solid

materials from outside the

cell.

Function 3: The lysosomal

membrane breaks down

following injury to, or death

of, the cell. The digestive

enzymes then attack the

cytoplasm in a destructive

process known as

autolysis. For this reason

lysosomes are sometimes

called “suicide packets.”

Peroxisome

• Peroxisomes are vesicles containing degradative enzymes

• smaller than lysosomes

• Two main functions:

• Breakdown organic compounds into hydrogen peroxide water

• Absorb and breakdown fatty acids

• Ex. most abundant in liver cells

Membrane flow 1. Nucleus: DNA

information Creates copy of DNA information (RNA) which travels to RER

2. RER uses RNA instructions to synthesize the protein

3. Protein is sent to Golgi for processing in a vesicle

4. Protein is modified in Golgi for secretion and placed into a secretory vesicle

5. Protein is released from the secretory vesicle via exocytosis

Intercellular attachment

There are three major types

of cell junctions:

• Communicating (gap)

junctions –found in heart

& smooth muscle

• Adhering (tight) junctions

- found in epithelium

• Anchoring junctions

(desmosomes)- found in

heart muscle and found

in layered epithelium

Tight junction

Anchoring junction

The Cell Life Cycle

INTERPHASE

THE CELL

CYCLE

MITOSIS AND CYTOKINESIS (See Figure 2.21)

Indefinite period G0

Specialized cell functions

G1 Normal cell functions plus cell growth, duplication of organelles, protein synthesis

G2 Protein synthesis

S DNA

replication, synthesis

of histones

M

Mitosis

• A cell divides to produce two identical cells

– To heal an injury

– To grow (increase cell number)

• Cells are not always dividing- most of their “life”

is spent between divisions (interphase G1)-

carrying out the organelle jobs

• Division costs lots in terms of energy!

• Uncontrolled cell division produces tumors

(cancers).

Stages of cell’s life cycle:

(PMAT) Interphase- (between divisions, can’t see chromosomes)

• G1- cell is not ready to divide, carries out normal functions

• S- cell commits to divide, and copies all the DNA

• G2- cell prepares for division, and generates more lipids and Proteins

Mitosis- Division of genetic information (division of the nucleus): think P.M.A.T. (“Passed My Anatomy Test”)

– Prophase- preparations (preliminary steps)- package chromosomes

– Metaphase- chromosomes line up in the middle of the cell

– Anaphase- chromosomes separate and the two halves move apart to opposite sides of the cell

– Telophase – chromosomes are surrounded by membranes to form two nuclei

Cytokinesis- Division of the cell into two identical cells

DNA Replication

KEY

Adenine

Guanine

Cytosine

Thymine

Segment 2

DNA polymerase

DNA nucleotide

DNA

polymerase

Segment 1

Interphase and Mitosis

INTERPHASE

MITOSIS BEGINS

EARLY PROPHASE LATE PROPHASE

Nucleus

Centrioles

(two pairs)

Astral rays Spindle

fibers

Centriole Chromosome

with two sister

chromatids

No chromosomes visible

Regular functions Chromosomes condense; Centrioles attach to them;

Microtubules form the “spindle”

METAPHASE ANAPHASE TELOPHASE INTERPHASE

CYTOKINESIS Metaphase

plate

Chromosomal

microtubule

Daughter

chromosomes

Cleavage

furrow

Daughter

cells

Chromosomes line

up in the middle

(metaphase plate)

Chromosomes

separate at the

centromere; each

identical chromatid

(piece of DNA) goes

to the opposite side

2 nuclei form 2 cells form

Interphase and Mitosis