Chapter 13 –RNA and Protein
Synthesis
Section 1 - RNA
RNA
• RNA stands for RiboNucleic Acid
• RNA is a nucleic acid; therefore, made of
nucleotides
• RNA works with DNA to make proteins
• Proteins are made through a process called
protein synthesis
• Review: Proteins are made of amino acids
• Review: Proteins are made by ribosomes
Phosphate
Nitrogen Base
5 – Carbon Sugar
- Ribose (if RNA)
- Deoxyribose (if DNA)
•
•
•
•
•
Guanine
Cytosine
Adenine
Thymine (only in DNA)
Uracil (only in RNA)
Differences between RNA and DNA
DNA
RNA
• Has the sugar deoxyribose
• Has the sugar ribose
• Double stranded - double helix • Single stranded
• Has thymine
• Has uracil
The Nucleotides of RNA
DNA has the 5-carbon sugar,
deoxyribose.
RNA has the 5-carbon sugar,
ribose.
DNA has thymine, adenine,
cytosine and guanine.
RNA has uracil, adenine,
cytosine and guanine.
DNA is a double stranded
molecule. It has base-pairs
with hydrogen bonds
between the nitrogen bases.
The molecule is anti-parallel.
RNA is a single stranded
molecule.
3 types of RNA
There are 3 major types of RNA:
1. Messenger RNA (mRNA) – carries the genetic
code from DNA to the ribosome (site of
protein synthesis)
2. Ribosomal RNA (rRNA) – makes the two
subunits of ribosomes
3. Transfer RNA (tRNA) – transports amino
acids (monomers of proteins) to the
ribosomes
3 types of RNA
Messenger RNA (mRNA) –
carries code from DNA to
ribosome for protein
synthesis
Ribosomal RNA (rRNA) –
assembles amino acids
brought by tRNA in a
specific order from mRNA
to make proteins; made of
RNA by the nucleolus
Transfer RNA (tRNA) –
transports specific amino acid
to ribosome for protein
synthesis
Production of RNA
• RNA is made through a process called
transcription
– “trans” – across
– “script” – to write
• DNA is split and one strand forms a template
• A sequence of DNA that codes for a protein is
known as a gene
• There are portions of DNA that do not code
for protein
Transcription
• DNA template is formed when it untwists and
hydrogen bonds between nitrogen bases are
broken
• RNA polymerase (an enzyme) binds
complementary nucleotides to the template
– Places Cytosine with Guanine
– Places Adenine with Thymine
– Places Guanine with Cytosine . . . BUT
– Place URACIL with Adenine
• RNA DOES NOT HAVE THYMINE!!
Transcription
Transcription
1. DNA “unzips”
2. One side of DNA becomes a
template
3. Free nucleotides of RNA attach to
open sites of the template by RNA
Polymerase (not shown)
• Cytosine attaches to Guanine
• Uracil attaches to Adenine
• Guanine attaches to Cytosine
• Adenine attaches to Thymine
4. Messenger RNA is produced and
released
5. mRNA is edited
• Introns removed
• Exons spliced together
6. mRNA goes to ribosomes for
protein synthesis
Another look at transcription . . .
Transcription (cont’d)
• Transcription starts at a location called the
promoter
• Promoter is a specific sequence of DNA that
starts transcription
• Pre-RNA is produced
• Introns are cut out and thrown out
• Exons are spliced together to form mRNA
• mRNA is sent to ribosomes to be decoded
Editing/Refining
• Introns and Exons are processed
• Introns are removed and exons are
placed together
• Exons are expressed; introns disappear
• Purpose of introns are not known
A sequence of nitrogen bases
on a segment of DNA of one
of its strands that actually
carries instructions for the
order of amino acids in a
protein is called a gene.
When DNA separates, one side
becomes the template. Which
side is the template? The side
that is a code for a protein!
After transcription, a molecule
of mRNA with codons is
produced.
During translation, each codon
of mRNA is matched with an
anti-codon on a tRNA
molecule with the amino acid
it carries.