DNA and RNA
SB2. Students will analyze how biological traits
are passed on to successive generations.
a. Distinguish between DNA and RNA.
b. Explain the role of DNA in storing and
transmitting cellular information.
d. Describe the relationships between changes in
DNA and potential appearance of new traits
including
• Alterations during replication.
Insertions
Deletions
Substitutions
• Mutagenic factors that can alter DNA.
High energy radiation (x-rays and UV)
Chemical
•Humans share 50% of their DNA with bananas.
•Cells can contain 6-9 feet of DNA. If all the DNA in your body
was put end to end, it would reach to the sun and back over 600
times.
•DNA in all humans is 99.9 percent identical. It is about one tenth
of one percent that makes us all unique, or about 3 million
nucleotides difference.
•DNA can store 25 gigabytes of information per inch and is the
most efficient storage system known to human. So, humans are
better than computers!!
•In an average meal, you eat approximately 55,000,000 cells or
between 63,000 to 93,000 miles of DNA.
•It would take a person typing 60 words per minute, eight hours a
day, around 50 years to type the human genome.
DNA is composed of units called NUCLEOTIDES, which are
composed of three sub-molecules:
1. 5-Carbon Sugar (deoxyribose)
2. Phosphate
3. Nitrogen Base (purine or pyrimidine)
DNA is composed of two
complimentary strands of nucleotides
joined by hydrogen bonds:
Adenine with Thymine (A-T or T-A)
They join with 2 hydrogen bonds
Cytosine with Guanine (C-G or G-C)
They join with 3 hydrogen bonds
DNA twists into a double helix
https://www.dnalc.org/resources/3d/23-dna-unzip.html
http://learn.genetics.utah.edu/content/molecules/builddna/
https://www.dnalc.org/resources/3d/07-how-dna-is-packaged-basic.html
1. DNA directs the machinery of a cell to make specific
proteins, and, therefore, DNA indirectly controls all of the
functioning of all living things.
2. DNA stores the hereditary information of an individual
3. DNA has the ability to mutate (change). This allows for
new characteristics and abilities to appear which may help
an individual to survive and reproduce (EVOLUTION).
4. Self replication: DNA has the ability to
make copies of itself
1. DNA replication is called ‘semi-conservative’.
2. Semi-conservative replication is the process in which the
original strands of DNA remain intact and act as
templates for the synthesis of duplicate strands of DNA.
3. One copy of a DNA molecule will split apart to make two
complete copies of itself. Each new DNA molecule is
made up of half of the old molecule and half of a new
molecule.
https://www.dnalc.org/resources/3d/03-mechanism-of-replication-basic.html
Replication– the copying of a DNA
strand
1. Helicase enzyme binds to the DNA and
unzips it.
2. DNA polymerase binds to the DNA at the
replication fork.
3. DNA polymerase adds new bases to both
strands, according to the base-pairing
rules.
4. The enzymes release from the DNA and
the new strands zip and wind back up.
Replication
Ribonucleic acid
-single stranded
-has uracil instead of thymine
-ribose instead of deoxyribose
The process by which RNA is made. Takes
place inside the nucleus.
https://www.dnalc.org/resources/3d/12-transcription-basic.html
Steps of transcription
1. RNA polymerase binds to the DNA molecule
and unwinds and unzips it.
2. RNA polymerase adds new RNA bases along
the DNA strand, according to the rules.
Wherever there is C, it adds G.
Wherever there is T, it adds A.
Wherever there is A, it adds U.
3. The RNA detaches from the DNA.
4. The DNA winds up and zips back up.
Three different types of RNA are
made by transcription.
• mRNA– messenger RNA (responsible for
carrying the message)
• tRNA– transfer RNA (carries amino
acids)
• rRNA– ribosomal RNA (found in
ribosomes)
The process by which proteins are made. Takes
place in the cytoplasm.
https://www.dnalc.org/resources/3d/15-translation-basic.html
1. mRNA reaches the ribosome
2. The ribosome reads the mRNA codons
3. tRNAs with matching anticodons come to
the ribosome
4. tRNAs carry amino acids
5. The ribosome assembles the amino acid
chain according to the mRNA code
6. The new protein (amino acid chain)
detaches from the ribosome
Translation is the last step of gene expression.
The genetic code–
matching the
mRNA nucleotides
to the amino acid
sequence. The
chart always refers
to the mRNA
codons.
What is the amino acid sequence for the following
mRNA chain?
GUU ACC UAU UCA UAA
Val - Thr - Tyr - Ser - stop
1) Mutations can occur
naturally or through
environmental factors.
Environmental mutagens
include some chemicals
(food additives, pesticides,
plastics) and radiations
(X-rays to UV light).
2) A gene mutation is a change of one or more
nucleotides in a single gene. There are 3 types.
a) Addition
b) Deletion
c) Substitution
GENE MUTATIONS
Deletion: one nucleotide base is left out. All of the amino acids after
a deletion will be wrong, so SHAPE and FUNCTION of protein are altered.
Ex. cystic fibrosis
Insertion: one extra nucleotide base is added. This will also change
the entire amino acid sequence of the protein, so SHAPE and FUNCTION
of protein are altered. Ex. Crohn’s disease
Substitution: when single bases or short pieces are replaced with
one another. Ex. muscular dystrophy; sickle-cell anemia
Insertions and deletions are also called frameshift mutations
because they change the way the subsequent amino acids are
read.
3. Chromosomal mutations: a mutation of all or part
of a chromosome. These affect many genes.
Example #1: crossing
over where one part of a
chromosome changes
places with another.
This can cause extra
pieces, missing pieces, or
the exchange of pieces of
chromosomes.
Example #2:
non-disjunction = extra
chromosomes or missing
chromosomes due to
mistakes made during
meiosis.