DNA Structure and Replication
• SC.912.L.16.9
• Explain why the genetic code is universal.
• Explain why there are similarities in the genetic code of different organisms.
• SC.912.L.16.3
• Describe the basic process of DNA replication.
• Explain why DNA replication has a role in the transmission and conservation of
the genetic material.
• Demonstrate the process of DNA replication given a DNA strand.
• SC.912.L.16.4
• Analyze the causes of gene and chromosomal mutations to predict the
possible effect in a DNA sequence.
• Explain how mutations in a DNA sequence may or may not result in a
phenotypic change.
• Explain how mutations in gametes may result in phenotypic changes in
offspring.
Why is the genetic code universal?
• All organisms have DNA made of the same
molecules.
– DNA in every organism has the bases: A,T,C,G
Why are there similarities in the
genetic code of similar organisms?
• Most organisms share a
common ancestry and
the process of
inheritance carries traits
from generation to
generation.
How does the process of DNA replication
enable genetic information to be
transmitted and used to build proteins?
• DNA  RNA  Protein
• DNA Replication= making an identical
copy of a DNA strand
• http://www.youtube.com/watch?v=_Q2Ba2cFAew
DNA Replication
• DNA replication begins with
the unwinding of the DNA
double helix by several
enzymes.
• The exposed strands are
then used as a template, or
model, to build the new
strand according to base
pairing rules (A to T, C to G).
• At the end of the process,
there are two, identical
strands of DNA, each with
part of the original strand
and a newly created strand.
Replication –
http://www.youtube.com/watch?v=4jtmOZaIvS0&safe=active
• Transcription is catalyzed by RNA polymerase.
– RNA polymerase and other proteins form a
transcription complex.
– The transcription complex recognizes the start of
a gene and unwinds a segment of it.
transcription complex
start site
nucleotides
– RNA polymerase reads one side of the DNA template
and strings together a complementary strand of RNA
nucleotides.
– The DNA helix winds again as the gene is transcribed.
DNA
RNA polymerase
moves along the DNA
– The RNA strand detaches from the DNA once the gene
is transcribed.
RNA
• RNA differs from DNA in three major ways.
– RNA has a ribose sugar.
– RNA has uracil instead of thymine.
– RNA is a single-stranded structure.
Transcription –
https://www.youtube.com/watch?v=WsofH466lqk
https://www.youtube.com/watch?v=HWzKxp8I-VU
Translation –
https://www.youtube.com/watch?v=5bLEDd-PSTQ
Codon – A sequence of three non-overlapping
nucleotides that code for a specific amino acid.
Anticodon – Nucleotides on the tRNA molecule that
help the molecule match up with the correct codon.
- complementary pairing.
Amino acids are coded by mRNA base
sequences.
• Translation converts mRNA messages into polypeptides.
• A codon is a sequence of three nucleotides that codes for
an amino acid.
codon for
methionine (Met)
codon for
leucine (Leu)
• Reading frame: series of non-overlapping nucleotides
read in order.
• A change in the order in which codons are read changes
the resulting protein.
• Regardless of the organism, codons code for the same
amino acid (common language).
Mutations are changes in DNA that may or may not
affect phenotype.
Some mutations affect a single gene,
while others affect an entire
chromosome.
• A mutation is a change in an organism’s DNA.
• Many kinds of mutations can occur, especially during
replication.
• A point mutation substitutes one nucleotide for another.
Mutated base
• Many kinds of mutations can occur, especially during
replication.
– A FRAME SHIFT MUTATION inserts or deletes a
nucleotide in the DNA sequence.
How can DNA mutate?
• Mutation = a mistake or change in the DNA
sequence.
– Causes: mistake during replication,exposure to xrays, ultraviolet light, radioactive substances or
certain chemicals.
Why don't all mutations result in visible
change?
• Not all mutations are
harmful, some may be
beneficial, and may not be
visible (silent mutation).
– Silent mutations occur
because the same amino acid
is created despite the error.
• https://www.youtube.com/watch?v=5qSrmei
Wsuc
1. Which of the following statements describes processes that occur during
DNA replication?
a. a DNA sequence is read by RNA polymerase, which produces another
RNA strand complementary to the first strand.
b.
Two free-floating single strands of DNA are joined by polymerase. The
polymerase finds the point at which the two strands will match up into a
double strand.
c.
Messenger RNA are decoded by a ribosome to produce an amino acid
chain. In the cell's cytoplasm, transfer RNA join the messenger RNA,
forming a polypeptide.
d.
A double-stranded DNA molecule is unwound into single strands.
Polymerase matches the right nucleotides to the single strand so that
each forms a double strand of DNA.
2. The genetic code is nearly universal, meaning that
almost all organisms use the same genetic code. Which
statement does NOT help explain why the genetic code is
nearly universal?
a. all organisms encode their genes using DNA or RNA
b. All organisms can grow, respond to stimuli, and
reproduce
c. All organisms use the same codon for the same amino
acid.
d. All organisms are genetically related to all other
organisms.
3. DNA mutations can be present in a gene for many
reasons. Which of the following does NOT describe a
reason genetic mutations may exist in a gene?
a. When a cell dies, the DNA in the cell's nucleus can
mutate.
b. Exposure to chemicals or radiation can cause
mutation in DNA.
c. Mutations in DNA can be passed down from a parent
to a child.
d. Polymerase can make a mistake in matching
nucleotides during replication.
4. Mutations in an organism's DNA may be either beneficial or harmful. Which
of the following statements best describes the concept of DNA mutation?
a.
b.
c.
d.
DNA mutation is an alteration in DNA replication that always results in
phenotypic change. Mutations are usually due to radiation or other
environmental factors
DNA mutation is a change in the way that genes reproduce themselves,
which may or may not affect phenotypic characteristics. Mutations are
usually due to environmental factors or heredity.
DNA mutation is a change in the gene sequence, which sometimes
results in phenotypic change. Mutations can be due to environmental
factors, heredity, or a mistake in DNA replication
DNA mutation is an alteration in the nucleus of a cell that makes certain
genes unable to be copied, and they result in phenotypic change.
Mutations are usually due to viruses and environmental factors