Download Lect 3 Introd to DNA

PowerPoint Lectures for
Introduction to Biotechnology, Second Edition
William J.Thieman and Michael A.Palladino
Chapter 2
An Introduction to Genes and
Genomes
Lectures by Lara Dowland
Copyright © 2009 Pearson Education, Inc.
Chapter Contents
• 2.1 A Review of Cell Structure
• 2.2 The Molecule of Life
• 2.3 Chromosome Structure, DNA Replication, and
Genomes
• 2.4 RNA and Protein Synthesis
• 2.5 Mutations: Causes and Consequences
Copyright © 2009 Pearson Education, Inc.
2.1 A Review of Cell Structure
• Plasma Membrane – double-layer structure of
lipids and proteins that surrounds the outer surface
of cells
• Cytoplasm – inner contents of a cell between the
nucleus and plasma membrane
• Organelles – structures in the cell that perform
specific functions
• Nucleous
Copyright © 2009 Pearson Education, Inc.
2.1 A Review of Cell Structure
• Prokaryotic Cells (include bacteria)
– No nucleus and no organelles
Copyright © 2009 Pearson Education, Inc.
2.1 A Review of Cell Structure
• Eukaryotic cells (plant cells, animal cells)
– Have a nucleus and many organelles
– Organelles
•
•
•
•
•
•
Nucleolus
Ribosomes
Mitochondria
Endoplasmic reticulum
Golgi apparatus
Lyzosomes
Copyright © 2009 Pearson Education, Inc.
2.1 A Review of Cell Structure
Copyright © 2009 Pearson Education, Inc.
2.1 A Review of Cell Structure
• Comparison of Prokaryotic and Eukaryotic Cells
Copyright © 2009 Pearson Education, Inc.
2.2 The Molecule of Life
• Evidence that DNA is the Inherited Genetic Material
– 1869
Friedrich Miescher: “nuclein”
• Could not be broken down by proteases
• Had acidic properties: “nucleic acids”
– 1928
Frederick Griffith
• Two strains of Streptococcus pneumoniae
– Virulent smooth strain (S cells) and harmless rough
strain (R cells)
• Demonstrated transformation – the uptake of DNA by
bacterial cells
Copyright © 2009 Pearson Education, Inc.
2.2 The Molecule of Life
Copyright © 2009 Pearson Education, Inc.
2.2 The Molecule of Life
• Evidence that DNA Is the Inherited Genetic
Material
– After Griffith's experiment of 1927, Rockefeller Institute researchers, worked
to extend his findings. Colin MacLeod worked to purify such solutions from
1934 to 1937, and the work was continued in 1940 and completed by
Maclyn McCarty.- in 1944
– 1944 Oswald Avery, Colin MacLeod, and Maclyn
McCarty provided evidences that DNA is the genetic
material
• Purified DNA from large batches of Streptococcus
pneumoniae
• Experiment proved that DNA was the transforming factor in
the Griffith experiments
• DNAase treatment avoid transformation to take place
Copyright © 2009 Pearson Education, Inc.
Evidence that DNA Is the Inherited Genetic Material
• 1952 – Alfred Hershey and Martha Chase provide
convincing evidence that DNA is the genetic
material:
• After a phage particle attaches to a bacterium, its DNA
enters through a tiny hole while its protein coat remains
outside. Key to the success of the experiment was showing
that viral infection was unaffected by violent agitation in a
kitchen blender which removed the empty viral protein
shells from the bacterial surface. The Hershey-Chase
experiment became known as the "blender experiment."
• Hershey-Chase Experiment
Used bacteria & bacteriophage,radioactive phosphorous in DNA
but not in proteins sulphur in protein capsulebut not in DNA:
The viral particles recovered after infection contained de
radioactive labeled DNA
Copyright © 2009 Pearson Education, Inc.
Hershey-Chase Experiment
http://www.youtube.com/watch?v=ne-8QSmGTpo
http://www.youtube.com/watch?v=zvWH8nsWQEo
Copyright © 2009 Pearson Education, Inc.
2
2.2 The Molecule of Life
• DNA Structure
– Building block of DNA is the nucleotide
– Each nucleotide is composed of
• Pentose (5-carbon) sugar called deoxyribose
• Phosphate molecule
• A nitrogenous base
– The nitrogenous bases are the interchangeable
component of a nucleotide
• Each nucleotide contains one base
– Adenine (A), thymine (T), guanine (G) or cytosine (C)
Copyright © 2009 Pearson Education, Inc.
The DNA molecule
Copyright © 2009 Pearson Education, Inc.
2.2 The Molecule of Life
Copyright © 2009 Pearson Education, Inc.
2.2 The Molecule of Life
• DNA Structure
– James Watson and Francis Crick revealed the definitive
structure of DNA
– “The Molecular Structure of Nucleic Acids: A Structure for
Deoxyribose Nucleic Acid” published in Nature on April
25, 1953
– This discovery had a major impact on genetics in
particular and biology in general.
– They used information from previous works
Copyright © 2009 Pearson Education, Inc.
2.2 The Molecule of Life
• DNA Structure
– Nucleotides are joined together to form long strands of
DNA and each DNA molecule consists of two strands
that join together and wrap around each other to form a
double helix
– Nucleotides in a strand are held together by
phosphodiester bonds
– Each strand has a polarity – a 5 end and a 3 end
Copyright © 2009 Pearson Education, Inc.
2.2 The Molecule of Life
• DNA Structure
– The two strands of a DNA molecule are held together by
hydrogen bonds
• Formed between complementary base pairs
• Adenine (A) pairs with thymine (T)
• Guanine (G) pairs with cytosine (C)
– The two strands are antiparallel because their polarity
is reversed relative to each other
Copyright © 2009 Pearson Education, Inc.
2.2 The Molecule of Life
Copyright © 2009 Pearson Education, Inc.
The DNA molecule
(Animation)
http://www.youtube.com/watch?v=qy8dk5iS1f0&feature=related
Copyright © 2009 Pearson Education, Inc.
2.2 The Molecule of Life
Genes:
• A gene is the basic unit of heredity in a living
organism.
• It can be defined as a sequence of nucleotides in the DNA
that codes (provides instruction) for the synthesis of a
particular polypeptide chain (most of them) or a particular
RNA
• Each gene determines a particular trait in the organism through the
synthesis of a specific enzyme for each metabolic reaction. Since DNA
is transmitted to the next generation, we inherit all traits from our parents
• Ex. The color of your eyes (several genes), type of hair, capability to
utilize lactose, etc
Copyright © 2009 Pearson Education, Inc.
2.3 Chromosome Structure, DNA
Replication, and Genomes
• Chromosome Structure
– Chromosomes – highly coiled and tightly condensed
package of DNA and proteins
• Occurs only during DNA replication
– Chromatin – strings of DNA and DNA-binding proteins
called histones
• State of DNA inside the nucleus when the cell is NOT
dividing
Copyright © 2009 Pearson Education, Inc.
2.3 Chromosome Structure, DNA
Replication, and Genomes
• Most human cells (Somatic cells) have two sets (pairs) of 23
chromosomes, or 46 chromosomes total (Diploid cells= 2n)
– Called homologous pairs
– Autosomes – chromosomes 1-22
– Sex chromosomes – chromosome pair # 23
• X and Y chromosomes
• Gametes (sex cells) contain a single set of 23
chromosomes (haploid number, n) (The 2n cells
reduce the chromosome number by Meiosis)
• When fertilization takes place, the zygote receives the 23 chromosomes
from the parent and 23 from the father, thus reestablishing the diploid (2n)
or regular number of chromosomes
Copyright © 2009 Pearson Education, Inc.
2.3 Chromosome Structure, DNA
Replication, and Genomes
3
• Chromosome consists of two thin, rod like
structures of DNA called sister chromatids
– They are exact replicas of each other copied during DNA
replication, just prior to chromosome formation
– During cell division, each sister chromatid is
separated
http://www.youtube.com/watch?v=BmDG_fKUTR8
Copyright © 2009 Pearson Education, Inc.
2.3 Chromosome Structure, DNA
Replication, and Genomes
• DNA Replication
– Cells divide by a process called mitosis
• Sex cells are produced by a slightly different process called
meiosis
– Mitosis
• One cell divides to form two daughter cells, each with an
identical copy of the parent cell DNA
• In order to accomplish this, the DNA of the parent cell must
be copied prior to mitosis
Copyright © 2009 Pearson Education, Inc.
2.3 Chromosome Structure, DNA
Replication, and Genomes
• DNA replication is Semiconservative
– Replication occurs in such a manner that, after
replication, each helix contains one original (parental)
DNA strand and one newly synthesized DNA strand
Copyright © 2009 Pearson Education, Inc.
2.3 Chromosome Structure, DNA
Replication, and Genomes
Copyright © 2009 Pearson Education, Inc.
2.3 Chromosome Structure, DNA
Replication, and Genomes
Steps in DNA Replication
1. Unwinding the DNA
–
Helicase enzyme breaks the hydrogen bonds holding the two
DNA strands together; “unzips” DNA
– DNA binding proteins hold the strands apart
– Separation of strands occurs in regions called origins of
replication
2. DNA polymerase synthesizes a new strand continually
from the leading strand (3’-5’)
3. Adding short segments of RNA in the lagging strand
–
–
Primase enzyme adds RNA primers
RNA primers start the replication process
Copyright © 2009 Pearson Education, Inc.
2.3 Chromosome Structure, DNA
Replication, and Genomes
Steps in DNA Replication
3. Copying the DNA
–
–
DNA polymerase enzyme binds to the
RNA primers
Uses nucleotides to synthesize complementary strands
of DNA
– Always works in one direction – 5’ to 3’
direction
Copyright © 2009 Pearson Education, Inc.
2.3 Chromosome Structure, DNA
Replication, and Genomes
http://www.youtube.com/watch?v=teV62zrm2P0&feature=related
Copyright © 2009 Pearson Education, Inc.
2.4 RNA and Protein Synthesis
• Transcription – genes are copied (transcribed)
from DNA code to RNA code
• Translation – RNA code is read into a protein
Copyright © 2009 Pearson Education, Inc.
2.4 RNA and Protein Synthesis
Copyright © 2009 Pearson Education, Inc.
2.4 RNA and Protein Synthesis
• Transcription
– Occurs only in genes
– RNA polymerase unwinds DNA helix and copies one
strand of DNA into RNA
• Binds to a promoter region
• Copies DNA in a 5’ to 3’ direction into RNA
• Uses nucleotides
– Adenine, uracil, guanine, and cytosine
– A-U, C-G
Copyright © 2009 Pearson Education, Inc.
2.4 RNA and Protein Synthesis
• Transcription
– At end of gene, RNA polymerase encounters the
termination sequence
• RNA polymerase and newly formed strand of RNA are
released from DNA molecule
– RNA strand is called a messenger RNA (mRNA)
– Multiple copies of mRNA are transcribed from each gene
during transcription
Copyright © 2009 Pearson Education, Inc.
2.4 RNA and Protein Synthesis
(transcription)
Copyright © 2009 Pearson Education, Inc.
2.4 RNA and Protein Synthesis
• mRNA Processing
– Initial mRNA produced is the primary transcript
• Immature and not fully functional
– A series of modifications before primary transcripts are
ready for protein synthesis
• RNA splicing
• Polyadenylation : The synthesis of a poly(A) tail, (all the
bases are adenines), at the end of an RNA molecule. )
• Addition of a 5’ cap (Modification that makes it more stable)
Copyright © 2009 Pearson Education, Inc.
2.4 RNA and Protein Synthesis
• How Is mRNA read?
– Genetic code – universal language of genetics used by
virtually all living organisms
•
•
•
•
•
Works in three nucleotide units of mRNA called codons
Each codon codes for a single amino acid
One amino acid may be coded for by more than one codon
Start codon
Stop codons
Copyright © 2009 Pearson Education, Inc.
2.4 RNA and Protein Synthesis
The Genetic Code
Copyright © 2009 Pearson Education, Inc.
2.4 RNA and Protein Synthesis
• Translation
– Occurs in the cytoplasm
– Function of each type of RNA
• mRNA – exact copy of the gene; carries the genetic code
from nucleus to the cytoplasm
• rRNA – component of ribosomes, the organelles
responsible for protein synthesis
• tRNA – transports amino acids to ribosome
Copyright © 2009 Pearson Education, Inc.
Protein Synthesis
Copyright © 2009 Pearson Education, Inc.
2.4 RNA and Protein Synthesis
Translation
1. Initiation – small ribosome subunit binds to 5’ end of
mRNA
–
Moves along the mRNA until the start codon is found
2. Elongation – tRNAs, carrying the correct amino acid,
enter the ribosome, one at a time, as the mRNA code
is read
3. Termination – ribosome encounters the stop codon
–
Newly formed protein is released
Copyright © 2009 Pearson Education, Inc.
2.4 RNA and Protein Synthesis
(Translation)
http://www.youtube.com/watch?v=
NJxobgkPEAo
Copyright © 2009 Pearson Education, Inc.
2.4Basics of Gene Expression Control
– Gene expression refers to the production of mRNA by a
cell
• All cells of an organism contain the same genome,
so how and why are skin cells different from brain
cells or liver cells?
– Because cells can regulate or control the genes they
express
Copyright © 2009 Pearson Education, Inc.
2.4 Basics of Gene Expression
Control
– Gene regulation is how genes can be turned on and off
in response to different signals
– Transcriptional regulation – controlling the amount of
mRNA transcribed from a particular gene
• Certain sequences found in the promotor region
– TATA box and CAAT box
• RNA polymerase cannot bind to promotor region without
presence of transcription factors
• Enhancer sequences bind to regulatory proteins called
activators
Copyright © 2009 Pearson Education, Inc.
2.4 Basics of Gene Expression
Control
– Bacteria use operons to regulate gene expression
• Organization of bacterial genes
• Clusters of several related genes located together and
controlled by a single promotor
• Operator – region within promotor
– Can use operons to regulate gene expression in
response to their nutrient requirements
• lac operon
Copyright © 2009 Pearson Education, Inc.
2.4 RNA and Protein Synthesis
Lac Operon
Copyright © 2009 Pearson Education, Inc.
2.4 RNA and Protein Synthesis
• Basics of Gene Expression Control
– RNA interference (RNAi) is a system within living cells
that helps determine what genes are active and how
active they are. Two types:
1) Small interfering RNAs (siRNAs) are small double
stranded RNA molecules that bind to mRNA, thus
blocking translation
2) microRNA (miRNA): Block translation or degrading
mRNA.
– In 1998, the American scientists Andrew Fire (MIT) and Craig
Mello (Harvard) published their discovery of this a mechanism
of DNA silencing. Subsequently they were awarded the 2006
Nobel Prize in Physiology or Medicine
Copyright © 2009 Pearson Education, Inc.
Differences between Prokariotes and
Eukariotes
The genes of Archaea and Bacteria
are organized into operons and are
transcribed into one polycistronic
mRNA, which encodes for more than
one gene product
Copyright © 2009 Pearson Education, Inc.
In Eukarya, a protein-encoding gene is
split into two or more coding regions
(exons), with noncoding regions
(introns) separating the coding
regions. The chromosomes are
located inside the nucleus, while
ribosomes are in the cytoplasm.
2.5 Mutations: Causes and Consequences
• Mutation – change in the nucleotide sequence of DNA
– Major cause of genetic diversity
– Can also be detrimental
• Types of Mutations
– Point mutations
• Silent mutations
• Missense mutations
• Nonsense mutations
• Frameshift mutations
Copyright © 2009 Pearson Education, Inc.
2.5 Mutations: Causes and Consequences
Copyright © 2009 Pearson Education, Inc.
2.5 Mutations: Causes and Consequences
• Gene mutations can be inherited or acquired
– Inherited mutations are those passed on to offspring
through gametes
– Acquired mutations occur in the genome of somatic cells
• Are not passed along to offspring
Copyright © 2009 Pearson Education, Inc.
2.5 Mutations: Causes and Consequences
• Mutations are a major cause of genetic diversity
– Human genomes are approximately 99.9% identical
• 0.1% differences in DNA between individuals, or one base
out of every thousand
– Roughly 3 million differences between different
individuals
• Most have no obvious effects; other mutations strongly
influence cell functions, behavior, and susceptibility to
genetic diseases
Copyright © 2009 Pearson Education, Inc.