Download DNA and RNA

DNA, RNA, and Mutations
Topic 20
I. DNA and RNA
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A. hereditary material - DNA and RNA
B. chemical structure of DNA – made of chains of
nucleotides
 1. Nucleotides - repeating units - has three parts
 a. phosphate
 b. deoxyribose - a five carbon sugar
 c. nitrogenous base – two types:
 (1) purines – larger and have two rings – include
adenine and guanine
 (2) pyrimidines – smaller – have one ring – include
thymine and cytosine
 (3) adenine always pairs with thymine and guanine
always pairs with cytosine
2. Watson-Crick model of DNA - two
chains of nucleotides in a ladderlike
structure - twisted double helix – created
their model of DNA using x-ray
photographs from Rosalind Franklin
 3. structure of DNA
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C. DNA replication
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1. The double stranded DNA molecules separates or
“unzips” along the weak hydrogen bonds between the
base pairs – helicase is the enzyme that initiates the
unzipping
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2. Free nucleotides present in the nucleus
attach themselves to the exposed bases - DNA
replication begins at specific locations called
replication origins -get two double strands of
DNA that are identical – primase is the enzyme
that initiates the attaching of the first
nucleotides and then DNA polymerase
continues the process
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3. semiconservative – each double strand of
DNA has one old strand and one new strand
4. travels from the 5’ end to the 3’ end (refers
the numbering of the carbons in the sugar
molecule)
5. DNA replication takes place on both strands
of DNA – they travel in opposite directions –
one is called the lagging strand and the other is
called the leading strand – the lagging strand
does not complete replication in one solid piece
– the small pieces are called the Okazaki
fragments – the leading strand completes
replication in one solid piece
6. DNA polymerase checks for mistakes
 7. ligase – the enzyme that is used to bond
the two pieces of DNA together
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DNA Replication
DNA Replication
DNA Replication
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http://www.stolaf.edu/people/giannini/flas
hanimat/molgenetics/dna-rna2.swf
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D. gene control of cellular activities
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1. Structure of RNA
a. a single strand
 b. ribose - 5 carbon sugar
 c. bases - uracil replaces thymine
 d. has phosphate group
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2. Types of RNA - three types of RNA
a. messenger RNA (mRNA) – carries the code
from DNA in the nucleus to the ribosome in
the cytoplasm (codon)
 b. transfer RNA (tRNA) – carries the
anticodon message and transports the
correct amino acid to the ribosome to meet
up with mRNA
 c. ribosomal RNA (rRNA) – connects the
amino acids in the correct order at the
ribosomes to make the protein
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3. Synthesis of RNA
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(1) Transcription - mRNA is found in the
nucleus – matches up with DNA code to form
a strand of RNA – each three nitrogenous
bases makes a codon which codes for an
amino acid – this is called transcription and
RNA polymerase is responsible for this
process
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(2) areas on the DNA are called promoters and
trigger the mRNA to attach – reads from the 5’ to 3’
end – modified before translation – special cap
added to the 5’ end and a poly A tail is added to
the 3’ end
RNA Transcription
(3) exons and introns - after the mRNA is made it is
modified - called splicing
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a. exons – part of the RNA that codes for the proteins
b. introns – part of the RNA code that is removed
Transcription
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(4). Protein synthesis - translation
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(1.) transfer RNA - makes an anticodon that matches a
codon on mRNA for a particular amino acid
(2.) aminoacyl-tRNA synthetases – attach amino acids
to the correct tRNA
(3.) mRNA carries the code to the ribosomes – tRNA
brings the anticodon and amino acid to the ribosome
– rRNA attaches the amino acids to each other in the
proper order to form the protein
(4.) tRNA and mRNA are released to go back to start
all over when needed
RNA Translation
Translation
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http://www.mun.ca/biology/scarr/An13_0
1_Protein_synthesis.mov
II. Mutations
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A. nature of mutations
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1. Definition - any change in the genetic or
hereditary material of a cell
2. Inheritable mutations - a mutation that occurs in
the primary sex cells (gametes) can be passed on
to future generations
3. Nonheritable mutations - a mutation that occurs
in a somatic cell (body cell) can’t be passed on to
future generations
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B. types of mutations – 2 basic types –
chromosomal alteration and gene
mutations
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1. Chromosomal alterations - any change in
the structure or number of chromosomes –
includes nondisjunction, translocation,
addition, and deletion
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a. nondisjunction - in meiosis if the chromosomes
don’t separate, you get cells with too many
chromosomes - Down’s syndrome and polyploidy
b. translocation - a section of a
chromosome is moved to
another nonhomologous
chromosome
c.
addition and deletion - gain or
loss of a part of a chromosome
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2. Gene mutations – change in the chemical
structure of the genetic material (DNA) –
includes missense, nonsense, insertion,
deletion, duplication, frameshift, repeat
expansion, and inversion
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A. missense – when a single base pair is changed. The new
code does not code for the proper amino acid which means that
the protein produced may be incorrect
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B. nonsense – when one base pair is changed and the
result is a stop codon that stops the production of a
protein
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C. insertion – addition of a single base pair which
changes the amino acids that are being coded for
which may change the protein being produced
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D. deletion – when one base pair is removed from the
sequence – changes the code for the amino acids
which may change the protein being coded for
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E. duplication – when a section of the DNA code is
replicated on the chromosome which increases the
length of the protein being produced
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F. frameshift – coding for the amino acids shifts over
one base pair so the code for the amino acids is
incorrect and therefore the protein produced may be
incorrect
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G. repeat expansion – a certain piece of the DNA
sequence is repeated over and over and over – the
amino acids are then repeated which may change the
protein being produced
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h. inversion – a piece of a chromosome is
flipped
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3. Most genetic mutations are recessive and
harmful to the individual
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C. mutagenic agents - materials that
cause mutations to occur at a greater
than normal rate - examples are
radiation (x-rays, uv rays) and chemicals
(formaldehyde, asbestos)
III. Genetic Diseases
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A. Tay Sachs - Tay-Sachs disease is a fatal genetic
lipid storage disorder in which harmful quantities of a
fatty substance called ganglioside GM2 build up in
tissues and nerve cells in the brain.
 The condition is caused by insufficient activity of an
enzyme called beta-hexosaminidase A that catalyzes
the biodegradation of acidic fatty materials known as
gangliosides
 Both parents must carry the mutated gene in order to
have an affected child
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B. PKU – Phenylketonuria (PKU) is a
birth defect in which a mutation occurs in
a gene containing instructions for making
the enzyme needed to break down the
amino acid phenylalanine. If the Phe
level gets too high, it can damage the
brain and cause severe mental
retardation.
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C. Down’s Syndrome – nondisjunction of
chromosome #21
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D. Sickle Cell Anemia - Sickle cell anemia is a
disease in which your body produces abnormally
shaped red blood cells. The cells are shaped like a
crescent or sickle. A genetic problem causes sickle
cell anemia. People with the disease are born with two
sickle cell genes, one from each parent.
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E. Huntington’s Disease - Huntington's
disease (HD) results from genetically
programmed degeneration of brain cells,
called neurons, in certain areas of the
brain. This degeneration causes
uncontrolled movements, loss of
intellectual faculties, and emotional
disturbance.
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F. Cystic Fibrosis - Cystic fibrosis (CF) is an
inherited disease of the mucus and sweat
glands. It affects mostly your lungs, pancreas,
liver, intestines, sinuses and sex organs. CF
causes your mucus to be thick and sticky. The
mucus clogs the lungs, causing breathing
problems and making it easy for bacteria to
grow. This can lead to problems such as
repeated lung infections and lung damage.
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G. Klinefelter syndrome – an extra X
chromosome in males – XXY – have
male sex organs but the testes are
abnormally small and the individual is
sterile – individual could also be XXXY
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H. Turner syndrome – females who lack
an X chromosome – XO – short stature –
web of skin between neck and back –
sterile – female sex organs don’t fully
develop