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DNA vs. RNA
DNA
• DNA – Deoxyribonucleic Acid
– Found in a cell’s nucleus
– Function: to carry genetic information
– Monomer: nucleotide
• 5 carbon sugar: deoxyribose
• Phosphate group
• Nitrogenous base
DNA, cont’d
Nitrogenous Bases
Adenine, Guanine, Cytosine, Thymine
Purines: 2 rings in
their structure
Adenine, Guanine
Pyrimidines: 1 ring
in their structure
Cytosine and Thymine
DNA, cont’d
Double Helix Shape
Sugar Phosphate Backbone:
“sides” of the ladder
Nitrogenous Base Pairs:
“steps” of the ladder
Adenine pairs with Thymine
Guanine pairs with Cytosine
Held together with
hydrogen bonds
RNA
• RNA – Ribonucleic acid
– Found in a cell’s cytoplasm and nucleus
– Function: helps to make proteins using DNA’s genetic
code
– Monomer: nucleotide
• 5 carbon sugar: ribose
• Phosphate group
• Nitrogenous base
– Nitrogenous Bases
• Adenine, Guanine, Cytosine,
• Uracil
– Shape
• Single Stranded
– There are three kinds of RNA
• mRNA, rRNA, tRNA
• mRNA (Messenger RNA)
– Carries set of instructions for assembling amino
acids from the DNA to the rest of cell
– long single strand of nucleotides
– Copies DNA into complementary codons
• A codon is a sequence of 3 nucleotides that are read as
a “word”
• A codon directs a specific amino acid to be used to
build a protein
•
ribosomal RNA: takes up the major part
of ribosomes; involved in protein
synthesis
•
transfer RNA: transfers each amino acid
to the ribosome
• tRNA (Transfer RNA)
– Responsible for converting
information found in
mRNA into a sequence of
amino acids, which build a
protein
– Contains an anticodon
• A sequence of bases
complementary to a
particular codon
– Transfers each amino acid
to the ribosome in a
process called translation
Comparing DNA and RNA
Compare/Contrast RNA and DNA
DNA
RNA
1.
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2.
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3.
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5.
5.
1.
2.
3.
4.
6.
Compare/Contrast RNA and DNA
DNA
RNA
1. Cytosine
1. Ribose sugar
2. Guanine
2. Half Ladder
3. Adenine
3. Uracil
4. Phosphate
4. Can leave the nucleus
5. Nucleus of cell
5. Translation
1. Deoxyribose sugar
2. Double ladder
3. Thymine
4. Replication
6. Transcription
PROTEIN SYNTHESIS (making proteins)
– Transcription – the process whereby DNA is
copied into mRNA into series of codons
• Steps:
1. RNA polymerase (notice the ase!) binds to DNA and separates the
strands
2. RNA polymerase uses the coding strand to then assemble a single
strand of mRNA
» Coding Strand: the side of the DNA strand that is used as a
template to make the complementary strand of mRNA
» Non-Coding Strand: the side of the DNA strand that is not
used to make mRNA
Translation Movie
1. Transcription
• Transcription is the
process whereby a
sequence of DNA is
copied into a
complementary
sequence of RNA.
THINK ABOUT IT
• Definition of TRANSCRIBE (from Miriam Webster
Dictionary)
• a : to make a written copy of
• b : to make a copy of (dictated or recorded matter) in
longhand or on a machine (as a typewriter)
• c : to paraphrase or summarize in writing
• d : write down, record
If you borrow someone’s notes you TRANSCRIBE (copy them).
You want to make an exact copy, to get all the info, but you
may make minor changes to help you understand it better.
TRANSCRIPTION: When copying the DNA a minor change is
made THYMINE  URACIL (something the RNA understands
better)
•During transcription, DNA is
unwound and separated by an
enzyme called RNA polymerase.
• RNA polymerase starts making the
copy of RNA at specific sites in the
DNA known as promoters.
• There are similar places in the DNA
that also tell the RNA polymerase to
stop. RNA polymerase uses one of
the strands to copy the genetic
information into a strand of RNA.
• Some parts of the original DNA strand contained
sequences of nucleotides called introns that are not
involved in coding for proteins.
• These must be taken out of the newly made RNA
strand. The remaining nucleotides that are involved in
coding for proteins are called exons. Now it is ready to
go as a mRNA molecule!
• DNA is “read” by RNA and copied into a
complementary strand. That strand tells the cell
which amino acids to make.
A
string of
amino acids is
known as a
protein.
Different
orders of
amino acids
make different
proteins.
mRNA
THINK ABOUT IT
Definition of TRANSLATE
(from Miriam Webster Dictionary)
• a : to turn into one's own or another language
In your foreign language courses you go back and
forth between languages. One does not
understand the other, but they have the same
meaning.
TRANSLATION: the language is changing from that
of NITROGEN BASES into that of AMINO ACIDS.
2. Translation
1. RNA is transcribed from DNA and released into the
cytoplasm
2. mRNA attaches to a ribosome.
3. Each codon is “read” and an amino acid is brought
INTO the ribosome by tRNA.
a. The first amino acid to be read is called the “start”
codon because it starts the process of
translation.
i. AUG: methionine
b. Each amino acid has its own specific tRNA
“carrier.”
c. One end of each tRNA has a specific amino acid
and the other end has three unpaired bases.
These bases are called the anticodon, and are
complementary to three bases on mRNA.
Translation Steps Cont.
4. The amino acid is strung together to make a
protein inside the ribosome by forming a
peptide bond between each amino acid and by
being removed from the tRNA molecule.
5. This process continues until the ribosome
reaches a stop codon on the mRNA molecule.
This signals the process of translation to stop
and a complete protein is now formed.
a. There are three stop codons: UAA, UAG, and UGA
DONE!!
• Now, a protein (chain of amino acids) has
been made by using transcription and
translation.
Transcription Animation!
http://www.biostudio.com/demo_freeman_
protein_synthesis.htm
• mRNA's instructions are called the GENETIC
CODE. The genetic code is read three letters
at a time, so each “word” is three bases long.
Remember that the bases of RNA are A, U, C,
and G; the “word” is written from these four
letters.
• The mRNA “word” that is three bases long is
called a codon. A codon is three consecutive
nucleotides long and specifies a single amino
acid.
Review…Importance
• Replication
– DNA copies itself before cell division so EACH cell has
identical instructions (blueprint)
• Transcription
– Makes the mRNA codons from DNA which describe
the specific order of amino acids needed to build a
protein
• Translation
– “reads” the mRNA codons and releases amino acids in
the correct order to make a protein
Questions to Think About…
Answer these with either transcription or
translation…
1. Which one should happen in the nucleus (if a
eukaryote)? (think about this!)
2. Which one makes mRNA?
3. Which one directly makes protein?
4. Which one occurs first?
5. Which one requires RNA polymerase?
12-5 PAP Gene Regulation
Only a fraction of genes are expressed
in a cell at any given time. Determining
whether a gene will be expressed or
“silent” depends on several different
structures. These different structures
are often regulatory sites that are next
to the promoter.
•
•
•
Prokaryote Gene Regulation
Prokaryotes are arranged in groups of genes
that are turned off and on together.
Operon – group of genes that operate
together
These genes are turned off by repressors and
turned on when RNA polymerase binds to the
promoter.
• On the DNA sequence there is a region where
repressors can bind and turn off the gene.
• Operator – region of the chromosome in an operon
to which the repressor binds when the operon is
turned off
• When the repressor is bound the gene is turned off
because it blocks RNA polymerase from binding
inhibiting transcription
Eukaryotic Gene Regulation:
Most eukaryotic genes are controlled
individually and have regulatory sequences
that are more complex than prokaryotic.
In eukaryotes, there is a short region of DNA
about 30 base pairs long with the sequence
TATATA or TATATAA, before the location
where transcription is to start. It is called the
TATA box and helps position RNA polymerase
by marking a point at which transcription
begins.
The genes in eukaryotes are regulated in a variety of
ways by enhancer sequences located before the
point at which transcription begins.
The genes in eukaryotes are regulated in a
variety of ways by enhancer sequences
located before the point at which transcription
begins.
At these enhancer sequences, different proteins
can bind. Some of these DNA binding proteins
enhance transcription by opening up tightly
packed chromatin or help attract RNA
polymerase. Others block access to genes.
Why is this regulation important?
• Eukaryotic gene regulation is complex because
of the level of complexity in a multicellular
organism. Every cell contains the complete
genetic code in their nucleus. Cell
specialization requires genetic specialization.
• Ex. The genes that code for liver enzymes are
not going to be expressed in nerve cells.
Development and Differentiation
• When an organism develops, regulation of
gene expression is extremely important. Every
specialized cell found in the adult develops
from the fertilized egg. In embryonic
development cells grow and divide and also
differentiate.
• Differentiation – process by which cells
become specialized in structure and function
• Differentiation of cells and tissues in the
embryo are controlled by a series of genes
called the hox genes. Mutations in these
genes can change the organs that develop in
specific parts of the body.
• Ex. Mutations in the hox genes of fruit flies
can replace the fly’s antennae with legs
growing on its head.
• The genes that control development are remarkably
similar in animals of common ancestors. The
common pattern of genetic control exists because all
of these genes have descended from the genes of
common ancestors.
• Ex. A gene that controls eye growth in fruit flies is
similar to that of the gene that controls eye growth
in mice. When a copy of the mouse gene was
inserted into the “knee” of the fly an eye grew on its
leg. Also, they are similar enough to trade places and
still function.