Chapter 7 Flashcards
What did scientists believe up until the early 1950s?
that proteins were the molecules that make up genes and constitute inherited material
Griffith (1927)
discovered the natural phenomenon known as bacterial transformation
What is bacterial transformation?
the ability of bacteria to alter their genetic makeup by absorbing foreign DNA molecules from other bacterial cells and incorporating the foreign DNA into their own.
What did Griffith work with?
different strains of the bacterium Diplococcus pneumoniae, which causes pneumonia
Avery , MacLeod, and McCarty (1944)
published findings that the molecule that Griffith’s bacteria was transferring was DNA
Avery , MacLeod, and McCarty (1944)
2nd discovery
Provided direct experimental evidence that DNA is the genetic material
Hershey and Chase (1952)
proved that DNA, not proteins, is the molecule of inheritance when they tagged bacteriophages (viruses that attack bacteria) with the radioactive isotopes 32P and 35S
32P labeled the
35S labeled the
dna of the phage viruses
protein coat of the phage viruses
Hershey + Chase found that when bacteria are infected with phage viruses
32p from the virus entered the bacterium and produced thousands of progeny. However, no 35s entered the bacterium
Rosalind Franklin (1950-53)
continued the work begun by Maurice Wilkins
-carrying out the xray crystallography analysis of dna that showed dna to be a helix
Her work helped watson and crick in
developing their model of DNA
Watson and Crick received the nobel prize in 1962 for
correctly describing the structure of dna as a double helix
Meselson and Stahl (1953)
proved Watsona and Crick’s hypothesis that DNA replicates in a semiconservative fashion
Meselson and Stahl’s experiment
they cultured bacteria (replicating bacteria in controlled settings) in a medium containing heavy nitrogen (15N) and then moved them to a medium containing light nitrogen (14N) allowing the bacteria to replicate and divide once
Results of Meselson and Stahl Experiment
new bacterial DNA contained DNA consisting of 1 heavy strand and 1 light one proving Watson and crick’s theory
Structure of DNA
- Double helix shaped like a twisted ladder
- Consists of 2 complementary strands running in opposite directions from each other
DNA is a
Polymer made of repeating units called nucleotides
Each nucleotide consists of a
DNA
5-carbon sugar (deoxyribose), a phosphate molecule, and a nitrogenous base
Each nucleotide contains
1 of 4 possible nitrogenous bases → adenine (A), thymine (T), cytosine ( C ), and guanine (G)
What does A bond with?
What does C bond with?
T
G
Nucleotides of opposite chains are paired to
ne another by hydrogen bonds
DNA replication is
the making of an exact replica of DNA
The 2 new molecules of DNA that are produced
each consist of 1 new strand and 1 old strand
this is called semiconservative replication
When does DNA replication occur?
during interphase in the life cycle of a cell
What does DNA polymerase do?
- catalyzes (speeds up reaction) the replication of the new DNA
- proofreads each new DNA strand, fixing errors and minimizing the occurrence of mutations
Where does DNA unzip?
at the hydrogen bonds that connect the two strands of the double helix
Each strand of DNA serves as a template for
the new strand according to the base-pairing rules → A w/ T, C w/ G
Each time the DNA replicates
some nucleotides from ends of chromosomes are lost
How does DNA protect itself against possible loss?
some eukaryotic cells have special nonsense nucleotide sequences at the ends of chromosomes that repeat thousands of times → called telomeres
RNA
single-stranded helix
Each nucleotide consists of
RNA
5-carbon sugar (ribose), phosphate, and a nitrogenous base
(RNA) Each nucleotide contains one of the four possible nitrogenous bases →
adenine (A), uracil (U), cytosine ( C), and guanine (G)
Uracil replaces thymine → no thymine in RNA
3 types of RNA
mRNA (messenger RNA), tRNA (transfer RNA), and rRNA (ribosomal RNA)
mRNA
carries messages directly from DNA in nucleus to the cytoplasm during the making of protein.
The triplet nucleotides of mRNA (such as AAC or UUU) are called
codons
tRNA
shaped like a clover leaf and carries amino acids to mRNA at the ribosome in order to form a polypeptide.
The triplet nucleotides of tRNA are
complementary to the codons of mRNA and are called anticodons
rRNA
structural, along with proteins, it makes up the ribosome.
rRNA
structural, along with proteins, it makes up the ribosome.
rRNA
structural, along with proteins, it makes up the ribosome.
Protein Synthesis
3 Main steps
transcription, RNA processing, and translation
Transcription
The process by which DNA makes RNA → facilitated by RNA polymerase and occurs in the nucleus
Transcription: The triplet code in DNA is transcribed
into a codon sequence in mRNA following the base-pairing rules → A w/ U and C w/ G
If the sequence in DNA triplets is AAA TAAA CCG GAC
The complementary sequence of codons in mRNA is: UUU AUU GGC CUG
RNA Processing
Initial transcript is processed or edited by a series of enzymes → after transcription but before the newly formed strand of RNA is shipped out of the nucleus to the ribosome
RNA processing:
Enzymes remove pieces of RNA that do not code for any protein→
non-coding regions that are removed are called introns (intervening sequences)
RNA processing:
The remaining portions, exons (expressed sequences or coding regions), are
pieced back together to form the final transcript
As a result of RNA processing, the mRNA that leaves the nucleus is a great deal
shorter than the piece that was initially transcribed
Translation of mRNA into Protein
Translation is the process by which the mRNA sequence is converted into an amin acid sequence
Translation of mRNA into protein occurs at
the ribosome
Translation of mRNA into Protein :
Amino acids present in the cytoplasm are carried by tRNA molecules to the
codons of the mRNA strand at the ribosome according the base-pairing rules ( A w/ U and C w/ U)
Some tRNA molecules can bind to
2 or more different codons
For ex, codons UCU, UCC, UCA, and UCG all code for a single amino acid, serine
Every cell does not constantly synthesize every
polypeptide it has the ability to make
Operon
is a cluster of functional genes plus the switches that turn them on and off
2 types of operons are
lac or inducible operon
repressible operon
Lac or inducible operon
is normally turned off unless it is actively induced or triggered to turn on by something in the environment
Repressible operon
is always turned on unless it is actively turned off bc it is temporarily not needed
Parts of the operon
promoter , operator, TATA box
Promoter
binding site of RNA polymerase
Promoter must always bind to DNA before
transcription can take place so the promoter is like an ‘on’ switch
Operator
binding site for the repressor which turns off the Lac operon
Operator
binding site for the repressor which turns off the Lac operon
TATA box (named for its sequences of alternating adenine and thymine)
helps RNA polymerase bind to the promoter
Changes in genetic material
occur spontaneously and at random and can be caused by mutagenic agents
Mutations are the
raw material for natural selection
Several gene mutations can occur :
point mutations, insertions, and deletions.
Point mutation
simplest mutation
a base-pair substitution, where one nucleotide converts to another
Ex. of point mutation
Normal: THE FAT CAT SAW THE DOG
becomes THE FAT CAT SAW THE HOG
Sickle cell anemia results from
point mutation in the gene that codes for hemoglobin
Abnormal hemoglobin causes RBCs to
sickle when available oxygen is low
When RBCs sickle, a variety of tissues may be
deprived of oxygen and suffer severe and permanent damage
Insertion or Deletion
results form a single nucleotide insertion or deletion (the addition or deletion of one letter in the DNA sequence)
(insertion/deletion) Both mutations result in
a frameshift bc the entire reading frame is altered and unreadable
A frameshift can
cause formation of altered polypeptide or no polypeptide at all
Chromosome Mutations
Alterations in chromosome number or structure and are visible under a microscope
Aneuploidy and polyploidy both result from nondisjunction
where homologous pairs fail to separate during meiosis
The human genome (an organism’s genetic material) consists of
3 billion base pairs of DNA and about 20,000 genes
97% of our DNA
doesn’t code for protein product
Some DNA consists of:
- regulatory sequences the control gene expressions
- Introns that interrupt genes
- (majority consists of) repetitive sequences that may repeat 10 million times and never get transcribed
- Psuedogenes → former genes that have accumulated mutations over a long time
Recombinant DNA means
taking DNA from 2 sources and combining them in one cell
Recombinant DNA is used in
genetic engineering or biotechnology
2 important areas of study in genetic engineering are
gene therapy and environmental cleanup
Microbes are also being engineered to
degrade oil at oil spills or decontaminate harmful chemicals at toxic mining sits or in water treatment plants
Growing concern about the safety about GMOs
- GMOs will be released into the wild spreading their engineered genes to wild species
- Foreign genes might adversely affect people who eat the genetically engineered organisms
Restriction Enzymes
An important tool for scientists working with DNA → cut DNA at specific recognition sequences or sites such as GAATC and are sometimes referred to as molecular scissors
The pieces of DNA that results form the cuts made by restriction enzymes are called
restriction fragments
100s of different restriction enzymes have been
isolated from bacteria
Gel Electrophoresis
Separates large molecules of DNA on the basis of their rate of movement through agarose gel in an electric field
Gel electrophoresis:
the smaller the molecule
the faster it runs through the gel
If necessary, the concentration of the agarose gel can be changed to
provide a better separation of the tiny DNA fragments
In order to run DNA through a gel, it must
be cut up by restriction enzymes into pieces small enough to migrate through the gel
Once separated on a gel,
the DNA can be analyzed in many ways
Polymerase Chain Reaction
Devised in 1985, PCRs are a cell-free, automated technique by which a piece of DNA can be rapidly copied or amplified
PCRs:
Billions of copies of a fragment of DNA can be produced in a few hours and once the DNA is amplified
these copies can be studied or used in a comparison with other DNA samples
