RNA

1
RNA Gene Expression
2
Gene Expression

• Making sense of the code and doing what it says!
• Even though the DNA in all of the cells of one
  organism are the same, they all dont perform the
  same functions
• Certain cells only express certain genes
• For example
• Eye cells dont express genes that relate to
  digestion
• Liver cells dont express genes that relate to
  reproduction
• Genes are expressed by way of proteins

3
Making a Protein

• Proteins are built according to instructions
  coded in DNA
• But, DNA does not directly make proteins
• RNA takes information from DNA to the ribosomes
  where the proteins are made
• Why?
• Proteins are made in two steps
• Transcription (DNA ? RNA)
• Translation (RNA ? Proteins)

4
DNA vs. RNA

• DNA is composed of two strands of nucleotides
  RNA is composed of one strand
• DNA and RNA have different types of sugars
  (deoxyribose vs. ribose)
• DNA has the bases A,T,C,G RNA has the bases
  A,U,C,G (Thymine is replaced by Uracil)

5
Types of RNA

• Messenger RNA (mRNA) Carries instructions from
  DNA to the ribosome
• Transfer RNA (tRNA) Translates the instructions
  into protein building blocks (amino acids)
• Ribosomal RNA (rRNA) What ribosomes are made up
  of

6
Transcription

• A process where information coded on a specific
  region of DNA (a gene) is transcribed (copied)
  into mRNA
• Occurs in nucleus
• Steps in transcription
• A certain segment of DNA strand unwinds and
  separates
• Complementary nucleotides are added (Adenine
  pairs with Uracil instead of Thymine)
• DNA strand joins back together and re-winds
• mRNA then travels out of nucleus to ribosome

7
Transcription
NUCLEUS
mRNA leaves nucleus
8
Three-Letter Words

• Every three nucleotide bases in mRNA is called a
  codon
• Each codon is matched to 1 of 20 amino acids
• The amino acids will later link up to form
  proteins

mRNA strand
9
Translation

• Translation uses the codons on the mRNA strand to
  link amino acids together to make proteins at the
  ribosome

Amino Acid
tRNA
C

• tRNAs anti-codon joins to mRNAs codon

A
U
anti-codon
codon
codon
codon
codon
codon
codon
A
G
U
G
G
G
C
A
A
A
A
G
C
U
C
G
G
U
10
Translation
G
U
codon
codon
codon
codon
codon
A
G
U
G
G
G
C
A
A
A
A
G
C
U
C
G
G
U
11
Translation
codon
codon
codon
U
U
C
A
G
U
G
G
G
C
A
A
A
A
G
C
U
C
G
G
U
12
Translation
codon
codon
codon
A
G
U
G
G
G
C
A
A
A
A
G
C
U
C
G
G
U
13
Translation
codon
codon
A
G
U
G
G
G
C
A
A
A
A
G
C
U
C
G
G
U
14
Translation
codon
A
G
U
G
G
G
C
A
A
A
A
G
C
U
C
G
G
U
15
Translation
Protein!
codon
A
G
U
G
G
G
C
A
A
A
A
G
C
U
C
G
G
U
16
Translation
17

• http//www.youtube.com/watch?v4PKjF7OumYo