DNA and Gene DNA and Gene ExpressionExpression

DNADNA

Deoxyribonucleic AcidDeoxyribonucleic Acid Double helixDouble helix Carries genetic Carries genetic

informationinformation Located in the nucleusLocated in the nucleus The monomer is a The monomer is a

nucleotidenucleotide– A phosphateA phosphate– A ribose sugarA ribose sugar– A nitrogenous baseA nitrogenous base

What are the bases in DNAWhat are the bases in DNA

A – adenineA – adenine T – thymineT – thymine C – cytosineC – cytosine G – guanineG – guanine Base pair rulesBase pair rules

Where is DNA located in the Where is DNA located in the Cell?Cell?

Where are the genes located?Where are the genes located?

Genes are located Genes are located on the on the chromosomes.chromosomes.

Every species has a Every species has a different number of different number of chromosomes.chromosomes.

There are two types There are two types of chromosomes: of chromosomes: autosomes and sex autosomes and sex chromosomeschromosomes

Genes are located on the chromosomes Genes are located on the chromosomes which are found in the nucleus of a cell. which are found in the nucleus of a cell.

When a cell is undergoing cell When a cell is undergoing cell reproduction, the chromosomes are reproduction, the chromosomes are visible. Chromosomes appear when visible. Chromosomes appear when the chromatin condenses and become the chromatin condenses and become visible.visible.

Most of the time (90%) the genetic Most of the time (90%) the genetic material in the form of chromatin.material in the form of chromatin.

A genome is the complete genetic A genome is the complete genetic information contained in an individual.information contained in an individual.– (gene + chromosome)(gene + chromosome)

What is gene expression?What is gene expression?

Gene expression is Gene expression is the activation of a the activation of a gene that results in gene that results in a protein.a protein.

Gene expression takes place Gene expression takes place differently in prokaryotes and differently in prokaryotes and

eukaryotes.eukaryotes. What is a What is a prokaryotes? Eukaryotes? prokaryotes? Eukaryotes?

ProkaryotesProkaryotes– No membrane No membrane

bound organelles bound organelles (nucleus)(nucleus)

– More primitive More primitive organismsorganisms

– Only one circular Only one circular chromosomechromosome

– Bacteria are the Bacteria are the only organisms that only organisms that are prokaryotes.are prokaryotes.

EukaryotesEukaryotes– Membrane bound Membrane bound

organelles ( specialize organelles ( specialize in function –nucleus, in function –nucleus, mitochondria, mitochondria, chloroplast)chloroplast)

– Chromosomes are in Chromosomes are in pairs and not circularpairs and not circular

– All organisms that are All organisms that are not bacteria: protist, not bacteria: protist, fungi, plants and fungi, plants and animalsanimals

In Eukaryotes, following mitosis or meiosis, In Eukaryotes, following mitosis or meiosis, DNA recoils but certain regions remain DNA recoils but certain regions remain relaxed for transcription. The areas of relaxed for transcription. The areas of relaxed DNA are called relaxed DNA are called euchromatineuchromatin..

Transcription is theTranscription is the

Reading of the DNA andReading of the DNA and

Changing the code toChanging the code to

mRNA.mRNA. Translation is changingTranslation is changing

The mRNA into a trait byThe mRNA into a trait by

Using tRNA to interpret theUsing tRNA to interpret the

mRNA.mRNA.

DNA in eukaryotes has regions of coding DNA in eukaryotes has regions of coding and noncoding DNA. The regions of DNA and noncoding DNA. The regions of DNA that code for proteins or traits are called that code for proteins or traits are called EXONSEXONS, while the regions that do not , while the regions that do not code for proteins are called code for proteins are called INTRONS.INTRONS.

cytoplasm cytoplasm

In prokayotes, transcription and In prokayotes, transcription and translation occur in the cytoplasm.translation occur in the cytoplasm.

In eukaryotes, transcription occurs In eukaryotes, transcription occurs inside the nucleus in a two step inside the nucleus in a two step sequence of events.sequence of events.– Pre-mRNA includes both introns and Pre-mRNA includes both introns and

exons for the gene.exons for the gene.– mRNA is only the coding portion (exons).mRNA is only the coding portion (exons).

Translation occurs in the cytoplasm at Translation occurs in the cytoplasm at the ribosomes.the ribosomes.– Reminder: The are three (3) types of Reminder: The are three (3) types of

RNARNA Messenager (mRNA)Messenager (mRNA) Transfer (tRNA)Transfer (tRNA) Ribsomal (rRNA)Ribsomal (rRNA)

TranslationTranslation RNARNA

– Single strandedSingle stranded– Does not contain Does not contain

thymine but has uracil thymine but has uracil instead.instead.

tRNA carries 3 base tRNA carries 3 base pair code for specific pair code for specific amino acid.amino acid.

Amino acids compose Amino acids compose polypeptid chains.polypeptid chains.

One or more One or more polypeptide chains polypeptide chains compose a proteincompose a protein

proteins provide the proteins provide the “blueprints” for our “blueprints” for our characteristics and characteristics and functions.functions.

In Prokaryotes there are three (3) In Prokaryotes there are three (3) regulatory elements that control regulatory elements that control gene expression.gene expression.

1.1. Structural genes – genes that code for Structural genes – genes that code for a specific polypeptide (protein).a specific polypeptide (protein).

2.2. Promoter – DNA segment that Promoter – DNA segment that recognizes RNA polymerase.recognizes RNA polymerase.

3.3. Operator – element that serves as a Operator – element that serves as a binding site for an inhibitor protein that binding site for an inhibitor protein that blocks transcription.blocks transcription.

Enhancer ControlEnhancer Control Eukaryote genes on Eukaryote genes on

a DNA strand also a DNA strand also have noncoding have noncoding control sequences control sequences that facilitate that facilitate transcription.transcription.

These are called These are called enhancers.enhancers.

Transcription factors Transcription factors are additional are additional proteins that bind to proteins that bind to RNA polymerase and RNA polymerase and enhancers to help enhancers to help with transcription.with transcription.

Cell DifferentiationCell Differentiation

Cell differentiationCell differentiation is the is the development of cells into cells with development of cells into cells with specialized functions.specialized functions.– Examples: muscle cells, liver cell, red Examples: muscle cells, liver cell, red

blood cellsblood cells As organisms grow and develop, As organisms grow and develop,

organs and tissues develop to organs and tissues develop to produce a characteristic form. The produce a characteristic form. The process is call process is call morphogenesis.morphogenesis.

Homeotic GenesHomeotic Genes Homeotic genes are Homeotic genes are

regulatory genes that regulatory genes that determine where certain determine where certain anatomical structures, such anatomical structures, such as appendages, will develop as appendages, will develop in an organism during in an organism during morphogenesis.morphogenesis.

These seem to be the These seem to be the master genes of master genes of developmentdevelopment

Normal Mutant with legs growing out of head

HomeoboxHomeobox In In DrosophilaDrosophila (fruit (fruit

flies) the specific DNA flies) the specific DNA sequence within a sequence within a homeotic gene that homeotic gene that regulates patterns of regulates patterns of development is the development is the homeoboxhomeobox. .

The same or very The same or very similar homeobox similar homeobox sequences have been sequences have been found in many other found in many other eukaryotic organismseukaryotic organisms

CancerCancer

Leading cause of death in the United Leading cause of death in the United StatesStates

A genetic disease caused by a A genetic disease caused by a mutation in the genes that control mutation in the genes that control cell divisioncell division

TumorTumor – abnormal proliferation of – abnormal proliferation of cells that results from uncontrolled, cells that results from uncontrolled, abnormal cell divisionabnormal cell division BenignBenign – a tumor that remains within a – a tumor that remains within a

massmass Malignant tumor-Malignant tumor- uncontrolled dividing uncontrolled dividing

cells that invade and destroy healthy cells that invade and destroy healthy tissue elsewhere in the bodytissue elsewhere in the body

MetastasisMetastasis – spread of cancer cells – spread of cancer cells beyond their original sitebeyond their original site

Kinds of CancerKinds of Cancer

Carcinomas Carcinomas – grow in skin and tissues – grow in skin and tissues that line the organs of the bodythat line the organs of the body– Example: lung and breastExample: lung and breast

SarcomasSarcomas – grow in bone and muscle – grow in bone and muscle tissuetissue

LymphomasLymphomas – solid tumors that grow – solid tumors that grow in tissues that form blood cellsin tissues that form blood cells– Example: leukemiaExample: leukemia

In In normal cells, that frequency of normal cells, that frequency of cell division is governed by cell division is governed by several factors:several factors:

1.1. Adequate nutritionAdequate nutrition2.2. Attachment to other cells, Attachment to other cells,

membranes or fibersmembranes or fibers3.3. Division stops if cell become Division stops if cell become

crowded (usually after 20 – 50) crowded (usually after 20 – 50) divisionsdivisions

Cancer cell continue dividing and Cancer cell continue dividing and ignore the normal messages to ignore the normal messages to stop dividingstop dividing..

What Causes Cancer?What Causes Cancer? Mutations that alter the genes Mutations that alter the genes

coding for growth factors.coding for growth factors.May occur spontaneouslyMay occur spontaneouslyResult from exposure to an Result from exposure to an

carcinogencarcinogen ( any substance that increases the risk ( any substance that increases the risk

of cancer.)of cancer.) Usually there is more than one Usually there is more than one

mutation.mutation. There are two types of genes that There are two types of genes that

control cell divisioncontrol cell divisionProto-oncogensProto-oncogensTumor suppressing genes (p53 gene)Tumor suppressing genes (p53 gene)