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RNA
Structure and Transcription and Translation

RNA is also known as Ribonucleic Acid
mRNA- Messenger RNA. Carries
instructions from the nucleus to
ribosomes.
 tRNA- Transfer RNA. Carries specific
amino acids to the ribosome
 rRNA- Ribosomal RNA. Component of
ribosome, connects amino acids together.

Types and Functions
rRNA
tRNA
mRNA
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Single-stranded polymer of nucleotides
Single Helix
Sugar-Phosphate backbone
◦ Ribose Sugar

4 types of nitrogen bases
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Adenine
Guanine
Cytosine
Uracil
 Takes the place of Thymine
Structure
"DNA makes RNA and RNA codes for
amino acids that are put together to make
proteins“
 Use this analogy:
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DNA is like a book
Chromosomes are like chapters of a book
Genes are like sentences in a chapter
Codons are like words of a sentence
Amino acids are like the meaning of the words
Central Dogma of Molecular
Biology
All of a humans DNA.
Divided into 23 pairs of
chromosomes.
Specific sections of
chromosomes are called
genes. Genes can be
3000-2.4 million basepairs long.
Protein Synthesis Overall
Creating mRNA from DNA
 DNA does not leave the Nucleus
 The DNA code needs to “written” in RNA
form that can leave the nucleus
 Process is similar to DNA replication on
the leading strand.

Transcription

Uses one strand of the DNA double helix
as a template:
DNA Template
AAGCTATACGGCAGTGAACCTGT
UUCGAUAUGCCGUCACUUGGAA
RNA Sequence
Transcription
The mRNA molecule leaves the nucleus
and travels to a ribosome in the
cytoplasm.
 The mRNA molecule is “read” by the
ribosome three bases at time.
 These are called codons.
 Each one codes for a different amino acid

Translation
Translation
Amino acids are carried to the ribosome
by tRNA molecules
 The top part of a tRNA molecule carries
the amino acid
 The bottom part has a 3 letter segment of
RNA called an “anti-codon”
 The anti-codon complements the codon
on the mRNA

Translation
tRNA
Small organelles in the cytoplasm that
assemble amino acids together to create
proteins
 Composed of two sub-units of rRNA and
proteins

The Ribosome
The small subunit reads the mRNA three
letters at a time
 The large subunit attaches the amino
acids together
 Three bonding sites:

◦A site (aminoacyl site)
◦P site (peptidyl site)
◦E site (Ejection site)
◦ *Just remember APE*
The Ribosome

The correct tRNA Attaches at the A site

The tRNA then moves the the P site where
its amino acid is Put onto the growing
chain
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The tRNA is the Ejected at the E site
Binding Sites

Raw sequence of mRNA transcribed from
DNA is actually Pre-mRNA and needs to
be modified before it can be read by the
ribosome.
Pre-mRNA Modifications

First, a “5’ cap” is added to the 5’ end of
the pre-mRNA
◦ Helps mRNA exit the nuclear pores
 Allows transport proteins to attach to the mRNA
strand
◦ Helps to prevent degradation of mRNA
◦ Helps mRNA “find” a ribosome
mRNA Modifications
Then a “poly-A” tail is added to the 3’ end
 A long 80-150 bases of Adenine are added
to the 3’ end

◦ Helps to prevent degradation of mRNA
◦ Helps with ending translation at the ribosome
mRNA Modification
Not all of the mRNA actually codes for
chains of amino acids.
 Segments that DO NOT code for amino
acids are called Introns
 Segments that DO code for amino acids
are called Exons

◦ Introns will be completely removed from an
mRNA molecule
◦ This is called “splicing”
Exons and Introns