DNA and Gene Expression

1
DNA and Gene Expression
2
DNA

• Deoxyribonucleic Acid
• Double helix
• Carries genetic information
• Located in the nucleus
• The monomer is a nucleotide
• A phosphate
• A ribose sugar
• A nitrogenous base

3
What are the bases in DNA

• A adenine
• T thymine
• C cytosine
• G guanine
• Base pair rules

4
Where is DNA located in the Cell?
5
Where are the genes located?

• Genes are located on the chromosomes.
• Every species has a different number of
  chromosomes.
• There are two types of chromosomes autosomes
  and sex chromosomes

6

• Genes are located on the chromosomes which are
  found in the nucleus of a cell.
• When a cell is undergoing cell reproduction, the
  chromosomes are visible. Chromosomes appear when
  the chromatin condenses and become visible.
• Most of the time (90) the genetic material in
  the form of chromatin.
• A genome is the complete genetic information
  contained in an individual.
• (gene chromosome)

7
What is gene expression?

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

8
Gene expression takes place differently in
prokaryotes and eukaryotes. What is a
prokaryotes? Eukaryotes?

• Prokaryotes
• No membrane bound organelles (nucleus)
• More primitive organisms
• Only one circular chromosome
• Bacteria are the only organisms that are
  prokaryotes.

• Eukaryotes
• Membrane bound organelles ( specialize in
  function nucleus, mitochondria, chloroplast)
• Chromosomes are in pairs and not circular
• All organisms that are not bacteria protist,
  fungi, plants and animals

9

• In Eukaryotes, following mitosis or meiosis, DNA
  recoils but certain regions remain relaxed for
  transcription. The areas of relaxed DNA are
  called euchromatin.
• Transcription is the
• Reading of the DNA and
• Changing the code to
• mRNA.
• Translation is changing
• The mRNA into a trait by
• Using tRNA to interpret the
• mRNA.

10

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

cytoplasm
cytoplasm
11

• In prokayotes, transcription and translation
  occur in the cytoplasm.
• In eukaryotes, transcription occurs inside the
  nucleus in a two step sequence of events.
• Pre-mRNA includes both introns and exons for the
  gene.
• mRNA is only the coding portion (exons).
• Translation occurs in the cytoplasm at the
  ribosomes.
• Reminder The are three (3) types of RNA
• Messenager (mRNA)
• Transfer (tRNA)
• Ribsomal (rRNA)

12
Translation

• RNA
• Single stranded
• Does not contain thymine but has uracil instead.
• tRNA carries 3 base pair code for specific amino
  acid.
• Amino acids compose polypeptid chains.
• One or more polypeptide chains compose a protein
• proteins provide the blueprints for our
  characteristics and functions.

13

• In Prokaryotes there are three (3) regulatory
  elements that control gene expression.
• Structural genes genes that code for a specific
  polypeptide (protein).
• Promoter DNA segment that recognizes RNA
  polymerase.
• Operator element that serves as a binding site
  for an inhibitor protein that blocks
  transcription.

14
Enhancer Control

• Eukaryote genes on a DNA strand also have
  noncoding control sequences that facilitate
  transcription.
• These are called enhancers.
• Transcription factors are additional proteins
  that bind to RNA polymerase and enhancers to help
  with transcription.

15
Cell Differentiation

• Cell differentiation is the development of cells
  into cells with specialized functions.
• Examples muscle cells, liver cell, red blood
  cells
• As organisms grow and develop, organs and tissues
  develop to produce a characteristic form. The
  process is call morphogenesis.

16
Homeotic Genes

• Homeotic genes are regulatory genes that
  determine where certain anatomical structures,
  such as appendages, will develop in an organism
  during morphogenesis.
• These seem to be the master genes of development

Mutant with legs growing out of head
Normal
17
Homeobox

• In Drosophila (fruit flies) the specific DNA
  sequence within a homeotic gene that regulates
  patterns of development is the homeobox.
• The same or very similar homeobox sequences have
  been found in many other eukaryotic organisms

18
Cancer

• Leading cause of death in the United States
• A genetic disease caused by a mutation in the
  genes that control cell division

19

• Tumor abnormal proliferation of cells that
  results from uncontrolled, abnormal cell division
• Benign a tumor that remains within a mass
• Malignant tumor- uncontrolled dividing cells that
  invade and destroy healthy tissue elsewhere in
  the body
• Metastasis spread of cancer cells beyond their
  original site

20
Kinds of Cancer

• Carcinomas grow in skin and tissues that line
  the organs of the body
• Example lung and breast
• Sarcomas grow in bone and muscle tissue
• Lymphomas solid tumors that grow in tissues
  that form blood cells
• Example leukemia

21

• In normal cells, that frequency of cell division
  is governed by several factors
• Adequate nutrition
• Attachment to other cells, membranes or fibers
• Division stops if cell become crowded (usually
  after 20 50) divisions
• Cancer cell continue dividing and ignore the
  normal messages to stop dividing.

22
What Causes Cancer?

• Mutations that alter the genes coding for growth
  factors.
• May occur spontaneously
• Result from exposure to an carcinogen
• ( any substance that increases the risk of
  cancer.)
• Usually there is more than one mutation.
• There are two types of genes that control cell
  division
• Proto-oncogens
• Tumor suppressing genes (p53 gene)