Transcript What is RNA, and How Does it Differ from DNA?

What is DNA, and How is it Used in
Today’s Society?
• Deoxyribonucleic Acid (DNA)
– DNA is found in all living things (all life related?)
– The hereditary material; found in the nucleus of
eukaryotes (copied before each cell division; passes
codes for physical traits to offspring)
– Today, segments of DNA (genes) can be manipulated,
and can be removed from/inserted into organisms
(biotechnology, transgenic organisms)
– Your DNA code is unique (excl. identical twins) 
criminal and paternity applications
– Genetic diseases linked to various genes  genetic
screenings and counseling
Figure 16.2
Figure 16.4
What is the Structure of DNA, and How
is it Copied Before Cell Division?
• Structure of DNA
– A polymer, composed of nucleotides (which consist of
a sugar, a phosphate group, and a nitrogenous base)
• Sugar is deoxyribose
• Nitrogenous bases: guanine, cytosine, adenine, and thymine
– Double-stranded molecule, wound in helix (Watson,
Crick, and Wilkins  Nobel Prize)
• Two strands joined by hydrogen bonds (two bonds between
T/A; three bonds between C/G); unzip at high
temperature or via enzyme action
• DNA Replication (occurs during S-phase)
– Code of new strand based on original template
– Enzymes involved: DNA Polymerase, Helicase
Figures 16.1
and 16.5
Figure 16.6
Figure 16.7
Figure 16.8
Figure (page 310)
Figure 16.9
Figures 16.10 and 16.11
Figure 16.13
Figure 16.14
Figure 16.17
What is RNA, and How Does it
Differ from DNA?
• Ribonucleic Acid – the Messenger Molecule
(and the Original Information Molecule)
– Single-stranded molecule; but can take threedimensional shapes (stem loops, hairpins)
– Sugar is ribose; bases: guanine, cytosine,
adenine, and uracil (vs. thymine of DNA)
– Three functional types (based on shapes)
• Messenger RNA (m-RNA): transmits message of gene
• Transfer RNA (t-RNA): 20 types (one for each of the
20 types of amino acids); work like enzymes
• Ribosomal RNA (r-RNA): associated with proteins to
form ribosomes
Figure 5.27
RNA HAIRPINS AND STEM LOOPS
RNA Hairpins: AGCCCGGUUCGAACCGGGCU

AGCCCGGUUC-I
UCGGGCCAAG-I
---------------------------------------------------------------------------------------------------
RNA Stem Loops: AGCCCGGUUUUUUCCGGGCU

UUU
AGCCCGGI U
UCGGGCCI U
U
What is the Role of RNA in Gene
Expression?
• Gene Expression:
Gene (DNA)  message (m-RNA)  polypeptide (protein)
TRANSCRIPTION
TRANSLATION
• Transcription (gene  m-RNA)
– Occurs in nucleus
– Nucleotide sequence of m-RNA based on code of DNA
(gene)
• RNA polymerase enzyme involved in process
– In eukaryotes, m-RNA often edited into exons and
introns; exons processed into mature m-RNA that
enters cytoplasm and is used for protein synthesis
Figure 17.3
Figure 17.7
Figures 17.9 and 17.10
Figures 17.11 and 17.12
How are Proteins Synthesized
Based on Genetic Instructions?
• Translation (Protein synthesis: m-RNA 
polypeptides)
– Occurs at ribosomes (in rough ER or cytoplasm)
– t-RNA, bound to amino acids, associates with ribosome
– Order of amino acids determined by GENETIC CODE:
m-RNA codons (base triplets) bind to anticodons of
t-RNAs; amino acids join (peptide bonds) to form
polypeptides
– Polyribosomes found in cells that exhibit high levels of
protein synthesis (when many copies of same polypeptide are routinely synthesized)
Figures 17.13
and 17.14
Figure 17.4 and 17.5
Figure 17.16
Figure 17.17
Figure 17.18
Figure 17.19
Figure 17.20
Overview of Gene Expression
AAAACTCCCGGTATGAACCATATAT
start
stop
TRANSCRIPTION

GAGGGCCAUACUUGG
TRANSLATION

glu – gly – his – thr – try
Figure
17.25
What are Genetic Mutations, and
What are Their Effects?
• Mutations: changes in DNA code; occur during replication
– Genetic Code with “wobbly” third base
• If AUU mutates to AUC?  no effect
• If AUU mutates to ACU?  threonine replaces isoleucine
– Change in amino-acid sequence may or may not change function of
protein; typically involves changes in shape or charge
– Point mutations: change in one base (often random; mutation rates
can be increased by mutagens)
• If wobble effect, no change in amino acid
• Enzymes repair mutations at given rate, can be “overwhelmed”
• Ex. Sickle-cell anemia: one of 146 amino acids in hemoglobin protein
“in error”
– Frame-shift mutations: large-scale error; shift in code
• Genetic Cancers
– Breast, ovarian, and colon cancers run in families (among others)
– Oncogenes: genes that are associated with high rates of cancers
– Tumor-suppressor genes: if mutated, more likely to develop cancer
Figure 17.23
Figure 18.22