GENE EXPRESSION

1
GENE EXPRESSION

• TRANSCRIPTION, TRANSLATION AND MUTATIONS

2
HOW DOES DNA, AS A GENE, GET EXPRESSED?

• DNA codes for specific proteins to be made
• proteins are assembled from amino acids
• amino acids are selected based on the genetic code

3

• Amino Acids will be bonded together to form long
  chains. These long chains are proteins.
• There are 20 different amino acids
• The DNA code dictates the sequence of acids

4
DNA to Proteins

• The process of making the proteins from DNA
  instructions is called PROTEIN SYNTHESIS
• Protein Synthesis has 2 major steps
• Transcription
• Translation

5
TRANSCRIPTION
Trans Across Script writing Writing across RNA
is being made (or written) using DNA Starts in
the nucleus with the chromosome which contains
the gene that will be expressed.
6

• As with replication--
• DNA unzips, but this time only in the gene
  location
• mRNA forms instead of another piece of DNA
• Uracil is substituted for Thymine
• only one strand is transcribed- called the
  sense strand- other strand is called the
  nonsense strand

7
WHAT IS A GENE?

• A gene is a section of a chromosome which codes
  for a specific trait

8

• After the DNA code is copied into the mRNA
  language, Transcription ends with the mRNA
  leaving the nucleus. (DNA is too big)

9
RNA

• needed to assist in the synthesis of proteins
• 3 types
• Messenger RNA (mRNA)
• Transfer RNA (tRNA)
• Ribosomal RNA (rRNA)

10
RNA STRUCTURE Differences from DNA

• 1.) Uracil instead of Thymine
• 2.) Single stranded
• 3.) Sugar is a Ribose Sugar

11
The strand of mRNA that forms is set up in 3-base
code words. Formed from nitrogen bases These
are called CODONS
12
Transcribe This DNA

• DNA
• ACTCAGACTATGACCTAGGATCAT
• TGAGTCTGATACTGGATCCTAGTA
• Consider bottom row as sense strand
• What will the 8 codons be in mRNA?

13
TRANSLATION

• Translating RNA into proteins
• Where are proteins made??
• RIBOSOMES
• Begins when mRNA travels to and enters the
  ribosomes
• Transfer RNA (tRNA) is out in the cytoplasm
  searching for amino acids
• Ribosomal RNA (rRNA) is in the ribosomes, helping
  place the mRNA in position

14
Each codon (mRNA) indicates which amino acid the
tRNA is suppose to bring to the
ribosomes. Scientists use a chart like this to
translate the protein. Example codon ACA AA
threonine
Fig. 14.11, p. 230
15
(No Transcript)
16
anticodon
codon in mRNA
anticodon
amino acid attachment site
amino acid
OH
tRNA MOLECULE
amino acid attachment site
Fig. 14.12, p. 231
17
C G anticodon 1 A U G anticodon
2 C C U anticodon 3 C G A anticodon
4 A G C anticodon 5 C U C anticodon
6 G A U anticodon 7 C
Once mRNA is at the ribosome, tRNA matches amino
acids to the codons using ANTICODONS Each tRNA
carries a different amino acid
18
Amino acid chain
tRNA
ribosome
anticodon
mRNA
codons
19
Binding site for mRNA
P (first binding site for tRNA)
A (second binding site for tRNA)
Fig. 14.14a, p. 232
20
Fig. 14.14b, p. 233
21

• Because there are only 20 amino acids, they are
  often called by their first three letters
• mRNA codons AUG CCG GAU UAG
• amino acids Met Pro Asp stop
• not all codons will code for an AA, some will be
  stop codons to tell translation to stop

start codon
22
(No Transcript)