Dr. Gary Mumaugh · Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. ... •DNA is a double helix strand of nucleotides, looking like a spiral

Cells Dr. Gary Mumaugh

Introduction

• The cell is the basic unit of biological organization

• Basic composition

– protoplasm

– cell membrane

– Organelles

• Human cells vary in size, shape and function

– From microscopic to up to two feet long

• There are 50-100 trillion cells in the human body.

• Differentiation is when cells specialize.

• There are over 260 different kinds of human cells.

• As a result of differentiation, cells vary in size and

shape due to their unique function

Anatomy of a Typical Cell

The Cell Membrane

• Double phospholipid layer with embedded

proteins – also called Plasma Membrane

– Protein functions of include forming channels

or pores, transporters, receptor sites for

hormones

• Cell membranes are selectively permeable

membranes

– Only certain substances can get through

• Not everything is on the “A” list !

Cytoplasm of the Cell

• Mostly water with chemical compounds

in solution or colloid

– Solution: atoms or ions distributed in

medium

• Polar compounds go into solution

• Nonpolar compounds go into colloidal

suspension

The Nucleus

• All human cells have a nucleus

– Except the RBC

• Control center of the cell

• Nuclear membrane has pores to allow substances

passage

• Chromatin genetic material (long threads of

chromosomes) are inside nucleoplasm

• Nucleolus - site of ribosome formation

Cytoplasm

• Is the watery solution of minerals, gases, organic

molecules and cell organelles that is found between

the cell membrane and the nucleus

• Cytosol is the water portion of the cytoplasm

• Many of the chemical reaction that occur in the cell

happen in the cytoplasm

Endoplasmic Reticulum (ER)

• System of membranes that makes up channels

• Connects with outer nuclear and cell membranes

• Types of ER

– Rough: for protein synthesis attached ribosomes

– Smooth: fat transport and sex hormone synthesis

Ribosomes

• Very small structures made up of protein and

ribosomal RNA

• Distributed throughout cytoplasm

• Attached to rough Endoplasmic Reticulum

• Site of protein synthesis

The Golgi Apparatus

• Secretion is the task of the Golgi apparatus

– They produce specific proteins to be used elsewhere

in tissues

– To secrete a substance, small sacs of the membrane

break off and fuse with the cell membrane, releasing

the substance to the outside of the cell

– This is called exocytosis

• Collection of flat saclike cisternae

• Concentration and collection of cellular compounds

• Storage warehouses of the cell

• Carbohydrate synthesis site

The Mitochondria

• Powerhouses of the cell

• The aerobic (oxygen requiring) reactions of cell

respiration take place here

• The site of ATP and energy production

• Cristae - inner folds where cellular respiration occurs

• Energy requirements of cell determine cristae

number

Lysosomes

• Digestive enzyme packages

• When WBC engulf bacteria, the bacteria are

digested and destroyed by lysosomal enzymes

• Worn out cell parts and dead cells are digested by

the lysosomes

• Function

– digest stored food

– maintenance and repair of organelles

– suicide agents for old or weak cells

Centrioles

• Involved in cellular division and reproduction

• Form spindle fibers during cell division

• Guide duplicated chromosomes to daughter cells

• Centrosome - two centrioles at right angles to each

other

Cilia and Flagella

• Hairlike protrusions from cell membrane

• Nine double fibrils around two single central fibrils

• Cilia move materials across cell surface

• Flagellum propels cell through a medium

Functions of Cell Organelles

• ER - Transport of materials in the cell

• Ribosomes – Site of protein synthesis

• Golgi apparatus – Cell secretion

• Mitochondria – ATP production, cell powerhouse

• Lysosomes – Digestive enzymes

• Centrioles – Cell division

• Cilia – Sweeps material across the cell surface

• Flagellum – Enables a cell to move

Think of the “Cell Factory”

Boss give orders to the rest of the factory (DNA in the

nucleus surrounded by the nuclear membrane). The

workers (ribosomes) on the assembly line are in the factory

(cytosol) who receive orders for production from the boss’s

messanger (mRNA). The raw materials are the amino

acids. When things are sent to the mailroom for outside

delivery (golgi apparatus), they are eventually shuttled to

the gates of the factory (secretory vessels).The gate of the

factory controls shipment in and out (cell membrane). The

turbines provide power for the factory (mitochondria).

Movement of Materials Into and

Out of Cells

Passive (Physical)

Processes

• Require no cellular

energy and include:

• Simple diffusion

• Facilitated diffusion

• Osmosis

• Filtration

Active (Physiological)

Processes

• Require cellular energy

and include:

• Active transport

• Endocytosis

• Exocytosis

• Transcytosis

Diffusion

• Movement of molecules from area of high

concentration to low concentration

• Brownian movement - random collision of diffusing

molecules

• Accelerated by increased temperature

• Gas exchange in the lungs of body tissue is an

example

– O2 - CO2 exchange

22

Animation: How Diffusion Works

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Facilitated Diffusion

• Facilitate means to help or assist

• Molecules move from an area of greater

concentration to an area of lesser concentration, but

they need help

– An example is glucose, which is need for ATP

production. Glucose can’t get through membranes by

themselves, so they have a carrier enzyme or

transporter to help facilitate diffusion

24

Animation: How Facilitated Diffusion Works













Animation: Diffusion Through Cell

Membranes













Osmosis

• Movement of water through semipermeable

membrane from high water concentration to low water

concentration

• Absorption of water by the small intestines and kidney

is an example

– Isotonic solution - salt concentration is the same outside

the cell as inside

– Hypotonic solution - salt concentration inside cell is

higher than outside cell

– Hypertonic solution -salt concentration higher outside

the cell than inside

27

Animation: How Osmosis

Works













• Osmotic Pressure – ability of osmosis to generate enough pressure to move a volume of water

• Osmotic pressure increases as the concentration of nonpermeable solutes increases

• Isotonic – same osmotic pressure

• Hypertonic – higher osmotic

pressure (water loss)

• Hypotonic – lower osmotic

pressure (water gain)

.

(b)

(a)

(c)

Active Transport

• The movement of molecules from and area of lesser

concentration to an area of greater concentration

• Opposite of diffusion

• Requires the energy of ATP to do this

• An example in the body is sodium and potassium

pumps in muscle and nerve cells

Filtration

• Water and dissolved materials are forced through a

membrane from an area of higher pressure to an

area of lower pressure

• In the body, blood pressure is an example of this,

with filtration occurring through the capillaries

Phagocytosis and Pinocytosis

• Phagocytosis

– A moving cell engulfs something

– WBC engulfing bateria

– Think of “pacman”

• Pinocytosis

– A stationary cell engulfs something

– Kidney cells absorbing lost protein

.

Endocytosis

• Cell engulfs a substance by forming a vesicle around

the substance

• Three types:

• Pinocytosis – substance is mostly water

• Phagocytosis – substance is a solid

• Receptor-mediated endocytosis – requires the

substance to bind to a membrane-bound receptor

Nucleus Nucleolus

V esicle Cell

membrane

33

Endocytosis

Cytoplasm

V esicle

(a) (b) (c) (d)

Receptor

protein

Cell

membrane

Molecules

outside cell

Cell

membrane

indenting

Receptor-ligand

combination

Nucleus Nucleolus

Particle Vesicle Phagocytized

particle

Cell

membrane

34

Exocytosis

• Reverse of endocytosis

• Substances in a vesicle fuse with cell membrane

• Contents released outside the cell

• Release of neurotransmitters from nerve cells

Nucleus

Endoplasmic

reticulum

Golgi

apparatus

DNA and the Genetic Code

• DNA is a double helix strand of nucleotides, looking

like a spiral ladder

– The rungs of the ladder are made up of four different

bases, arranged in different orders and sequences

– These sequences are the genetic code

– The DNA of our 46 chromosomes is the genome

which contains 20,000 to 30,000 genes

• If there is a mistake in the DNA, the result is genetic

or hereditary disease

RNA and Protein Synthesis

• Protein Functions

– structure, enzymes or catalysts, immune response

• Transcription Messenger RNA copies DNA code,

leaves nucleus

• Translation (tRNA) picks up amino acids

Cell Division

• Cell division is the process by which a cell

reproduces itself

• Two types of cell division

– Mitosis

– Meiosis

Mitosis

• One cell with the diploid number of chromosomes

divides once to form two cells, each with the diploid

number of chromosomes (46)

• Stages of mitosis

– Prophase, metaphase, anaphase, telophase

• Mitosis is essential for growth and for repair and

replacement of damaged cells

• Most nerve and muscle cells seem unable to divide and

their loss may involve permanent loss of function

Meiosis: A Reduction Division

• Reduces genetic material from diploid to haploid

• Two divisions resulting in four cells

• Occurs only in the gonads

– In women, meiosis takes place in the ovaries and is

called oogenesis

– In men, meiosis takes place in the testes and is called

spermatogenesis

• Fertilization is the egg uniting with the sperm

Comparison of Mitosis and Meiosis

Mitosis Meiosis

Two daughter cells with exact same genetic material

Four daughter cells with half the genetic material

Cellular division for growth, maintenance and repair

Cellular division for reproduction

41

3.5: Control of Cell Division

• Cell division capacities vary greatly among cell types • Skin and blood cells divide often and continually

• Neuron cells divide a specific number of times then cease

• Chromosome tips (telomeres) that shorten with each mitosis

provide a mitotic clock

• Cells divide to provide a more favorable surface area to

volume relationship

• Growth factors and hormones stimulate cell division • Hormones stimulate mitosis of smooth muscle cells in uterus

• Epidermal growth factor stimulates growth of new skin

• Tumors are the consequence of a loss of cell cycle control

• Contact (density dependent) inhibition

Tumors

• Two types of tumors:

• Benign – usually remains localized

• Malignant – invasive and can metastasize; cancerous

• Two major types of genes

cause cancer:

• Oncogenes – activate other genes that increase cell division

• Tumor suppressor genes – normally regulate mitosis; if

inactivated they are unable to

regulate mitosis

• Cells are now known as

“immortal”

Normal cells

(with hairlike cilia)

Cancer cells

Cellular Metabolism

• Metabolic processes – all chemical reactions that

occur in the body

There are two (2) types of metabolic reactions:

• Anabolism

• Larger

molecules are

made from

smaller ones

• Requires energy

• Catabolism

• Larger molecules

are broken down

into smaller ones

• Releases energy

Anabolism

• Anabolism provides the materials needed for

cellular growth and repair

• Dehydration synthesis

• Type of anabolic process

• Used to make polysaccharides, triglycerides, and

proteins

• Produces water CH2OH

H H

OH

O

H OH

Monosaccharide +

H HO

H

OH

H H

OH

O

H OH

Monosaccharide

H HO

H

OH

H H

OH

O

H OH

Disaccharide

H2O

Water +

H HO

H H H

OH

O

H OH

H O

H

OH

.

CH2OH CH2OH CH2OH

Catabolism

• Catabolism breaks down larger molecules into smaller ones

• Hydrolysis

• A catabolic process

• Used to decompose carbohydrates, lipids, and proteins

• Water is used to split the substances

• Reverse of dehydration synthesis

CH2OH

H H

OH

O

H OH

Monosaccharide +

H HO

H

OH

H H

OH

O

H OH

Monosaccharide

H HO

H

OH

H H

OH

O

H OH

Disaccharide

H2O

Water +

H HO

H H H

OH

O

H OH

H O

H

OH

CH2OH CH2OH CH2OH

46

Control of Metabolic Reactions

• Enzymes

• Control rates of metabolic reactions

• Lower activation energy needed to start reactions

• Not consumed in chemical reactions

Product molecule

Active site

(a) (b) (c)

Substrate molecules

Unaltered

enzyme

molecule

Enzyme-substrate

complex

Enzyme

molecule

.

47

Animation: How Enzymes Work













Factors That Alter Enzymes

• Factors that alter enzymes:

• Heat

• Radiation

• Electricity

• Chemicals

• Changes in pH

49

Energy for Metabolic Reactions

• Energy is the capacity to change something; it

is the ability to do work

• Common forms of energy:

• Heat

• Light

• Sound

• Electrical energy

• Mechanical energy

• Chemical energy

Dr. Gary Mumaugh · Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. ... •DNA is a double helix strand of nucleotides, looking like a spiral

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