Download RIBONUCLEIC ACID (RNA) NOTES

KEY
Introduction to Gene Expression
RNA Structure
HOW IS RNA DIFFERENT FROM DNA?
DNA (Deoxyribonucleic Acid)
o Contains the sugar deoxyribose
o adenine pairs with thymine
o cytosine pairs with guanine
o double stranded
RNA (Ribonucleic acid)
o Contains the sugar ribose
o adenine pairs with URACIL
o cytosine pairs with guanine
o single stranded
Is uracil a purine or a pyrimidine? pyrimidine How do you know? It has to be the same thing thymine is
So…(Fill in the chart)
Table 1. Differences between DNA and RNA
DNA
5-carbon sugar
RNA
Deoxyribose
Ribose
A-T, G-C
A-U, G-C
Double helix
Single strand
Nitrogen bases
Shape of Molecule
Let’s Practice:
DNA Replication (Review)
Strand 1 (old strand) Strand 2 (new strand)
A
T
G
C
C
A
A
T
_T_
_A_
_C_
_G_
_G_
_T_
_T_
_A_
RNA Synthesis (Transcription)
DNA Template Strand
RNA Sequence
A
T
G
C
C
A
A
T
_U_
_A_
_C_
_G_
_G_
_U_
_U_
_A_
Compare Strand 2 (the new strand you wrote the sequence for) in DNA Replication to the RNA sequence that
resulted from RNA synthesis. What do you notice? The strands are identical except that in the RNA
sequence resulting from transcription have uracil (U) instead of thymine (T)
Where in the cell does RNA synthesis occur? The nucleus
What is RNA synthesis actually called? Transcription
What happens to the DNA molecule that was unzipped so that RNA synthesis (transcription) could occur? The
double helix closed back up and it is still in the nucleus for use by the cell
Where does the RNA molecule that was just made go now? Into the cytoplasm
How does it get out of the nucleus? Through a nuclear pore
RNA Function:
WHY IS RNA IMPORTANT?
What are the three types of RNA messenger RNA or mRNA, transfer RNA or tRNA, and ribosomal RNA or
rRNA
Fill in the blanks to describe the function of each of the 3 types of RNA.
Messenger RNA (mRNA) transcribes the code from DNA and takes it from the nucleus into the cytoplasm at
the ribosome.
Transfer RNA(tRNA) translates the message by transferring amino acids from the cytoplasm to the
ribosomes based on the instructions in the mRNA.
Ribosomal RNA (rRNA) is a structural component of ribosomes that binds mRNA and tRNA together (most
RNA in a cell is rRNA).
RNA contains the message from the DNA that is needed by the cell to make proteins.
Proteins:
WHAT ARE PROTEINS?
Proteins are organic compounds (compounds that contain carbon) that are made from amino acids (aa or AA)
linked together by a type of covalent bond called a peptide bond.
Ex. AA1 + AA2 + AA3 = a protein/polypeptide
WHY ARE PROTEINS IMPORTANT?



--help build cell organelles (found in the membranes)
--are used as enzymes to promote reactions
--are found in muscles (actin & myosin), blood (hemoblogin), insulin, and antibodies, as
well as hair, silk, and other body structures (skin, bones, ligaments, tendons, etc)
HOW ARE PROTEINS MADE?
Proteins are made in the process of protein synthesis also called gene expression. There are two parts to this
process: transcription and translation. These processes mainly occur in the G1 phase of Interphase in the
Cell Cycle.
Transcription:
Transcription is when a molecule of DNA untwists and one strand is read to make a molecule of RNA. It occurs in
the nucleus.
Here is a diagram showing transcription.
Let’s “practice” transcription again.
DNA
3’T A C G C T A G T C C G T C5’
mRNA 5’A U G C G A U C A G G C A G3’
Translation:
Translation is when an mRNA molecule is “read” in the cytoplasm at a ribosome, and tRNA molecules bring amino
acids in the order indicated by the nucleotide sequence of the mRNA molecule to be hooked together into a
polypeptide (protein).
Here is a diagram showing translation.
Write the number of the structure indicated in
the diagram next to the correct name.
amino acids
1_
anticodon
4
mRNA
3
polypeptide
2
ribosome
5
1
2
5
4
3
Let’s practice translating a message. Start by transcribing the DNA sequence given into a molecule of mRNA.
Divide the mRNA into codons by drawing a line between every 3 nucleotides in the mRNA code. Then, write the
anticodons that would be found on the corresponding tRNA molecule. Finally, use the codon chart to determine
which amino acid is coded for by the sequence in the mRNA.
DNA Sequence:
T A C G G G T T C A A C T T G A C T
mRNA Sequence:
(codons)
A U G C C C A A G U U G
A A C U G A
U A C G G G U U C A A C
U U G A C U
tRNA Sequence:
(anticodons)
Amino Acid Sequence:Start/met
pro
lys
leu
How many codons did you write? 6 How many anticodons did you write? 6
coded for (BE CAREFUL! Stop is NOT an amino acid)? 5
asp
stop
How many amino acids were
Overview of Protein Synthesis (Gene Expression):
What are the structures labeled 1 & 2?
Nucleus/nuclear envelope & cytoplasm
1
This diagram shows only 1 ribosome
translating the message from the mRNA into
the polypeptide (amino acid sequence). Is
this accurate? No Explain. Hundreds of
ribosomes translate the mRNA at the
same time so that there is time for the
process to finish
When there is an error in the DNA (a
mutation), what can happen to the protein?
It can be nonfunctional, could stay the
same, not made at all, could be different
If you inherited a trait from one of your
parents, where is this trait coded for in you?
In my DNA (genes)
If red flowers are RR or Rr and white flowers
are rr, explain why these two alleles are
EXPRESSED differently. The R allele codes
for a protein that is a red pigment while
the r allele does not code for the
synthesis of any molecule
2
On the lines in this box, write WHERE in the cell each process occurs. Be specific.
_____________
_nucleus______
________
________________
cytoplasm at the
ribosome_________
_______