RNA
Ribonucleic Acid
Ribonucleic Acid (RNA)
 RNA is much more abundant than DNA
 There are several important differences between
RNA and DNA:
- the pentose sugar in RNA is ribose, in DNA it’s
deoxyribose
- in RNA, uracil replaces the base thymine (U pairs
with A)
- RNA is single stranded while DNA is double
stranded
- RNA molecules are much smaller than DNA
molecules)
Structure of RNA
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Single stranded
Ribose Sugar
5 carbon sugar
Phosphate group
Adenine, Uracil, Cytosine, Guanine
Types of RNA
 Three main types
 Messenger RNA (mRNA) – transfers
DNA code to ribosomes for translation.
 Transfer RNA (tRNA) – brings amino
acids to ribosomes for protein synthesis.
 Ribosomal RNA (rRNA) – Ribosomes are
made of rRNA and protein.
Transcription
 RNA molecules are produced by copying part
of the nucleotide sequence of DNA into
complementary sequence in RNA, a process
called transcription.
 During transcription, RNA polymerase binds to
DNA and separates the DNA strands. RNA
polymerase then uses one strand of DNA as a
template from which nucleotides are
assembled into a strand of mRNA.
mRNA
How Does it Work?
 RNA Polymerase looks for a region on
the DNA known as a promoter, where it
binds and begins transcription.
 RNA strands are then edited. Some
parts are removed (introns) - which are
not expressed – and other that are left
are called exons or expressed genes.
The Genetic Code
 This is the language of mRNA.
 Based on the 4 bases of mRNA.
 “Words” are 3 RNA sequences called
codons.
 The strand aaacguucgccc would be
separated as aaa-cgu-ucg-ccc the amino
acids would then be Lysine – Arginine –
Serine - Proline
Genetic Codes
Translation
 During translation, the cell uses information
from messenger RNA to produce proteins.
 A – Transcription occurs in nucleus.
 B – mRNA moves to the cytoplasm then to the
ribosomes. tRNA “read” the mRNA and obtain
the amino acid coded for.
 C – Ribosomes attach amino acids together
forming a polypeptide chain.
 D – Polypeptide chain keeps growing until a
stop codon is reached.
Protein Synthesis
 The two main processes involved in protein synthesis are
- the formation of mRNA from DNA (transcription)
- the conversion by tRNA to protein at the ribosome
(translation)
 Transcription takes place in the nucleus, while translation
takes place in the cytoplasm
 Genetic information is transcribed to form mRNA much the
same way it is replicated during cell division
Translation to Protein
Mutations
 Gene mutations result from changes in a
single gene. Chromosomal mutations
involve changes whole chromosomes.
Gene Mutation
 Point Mutation – Affect one nucleotide
thus occurring at a single point on the
gene. Usually one nucleotide is
substituted for another nucleotide.
 Frameshift Mutation – Inserting an extra
nucleotide or deleting a nucleotide
causes the entire code to “shift”.
Gene Mutation
Chromosomal Mutations
 Deletion – Part of a chromosome is deleted
 Duplication – part of a chromosome is
duplicated
 Inversion – chromosome twists and inverts the
code.
 Translocation – Genetic information is traded
between nonhomologous chromosomes.
Chromosomal Mutations
Mutations
More Mutations
Gene Regulation
 In simple cells (prokaryotic) lac genes
which are controlled by stimuli, turn
genes on and off.
 In complex cells (eukaryotic) this process
is not as simple. Promoter sequences
regulate gene operation.
Review