Download What is the function of DNA?

What is the function of DNA?
• Making proteins
• When genes are expressed, proteins are
synthesized
• It involves two stages – transcription and
translation
Learning Outcomes
• Explain the processes involved in
transcription
• The different nucleic acid needed and its
structure
• Explain the difference between primary and
mature transcript
DNA recap .... answer these ...
1.
2.
3.
4.
5.
6.
An examples of? MY LOPER
Made up of?
Different types of bases?
Number of strands?
Held by?
What is the triplicate code?
DNA and RNA are polymers of nucleotides
DNA is a nucleic acid, made of long chains of
nucleotides
Phosphate
group
Nitrogenous
base
Sugar
Phosphate
group
Nitrogenous base
(A, G, C, or T)
Nucleotide
Thymine (T)
Sugar
(deoxyribose)
DNA nucleotide
Polynucleotide
Sugar-phosphate backbone
• DNA has four kinds of bases, A, T, C, and G
Thymine (T)
Cytosine (C)
Pyrimidines
Adenine (A)
Guanine (G)
Purines
Figure 10.2B
DNA recap .... answer these ...
1. An examples of? Polymer
2. Made up of? Nucleotides (deoxyribose,
phosphate and base)
3. Different types of bases? Arginine,
Thymine, cytosine, guanine
4. Number of strands? 2
5. Held by? Weak hydrogen bonds between
strands, covalent bonds between
nucleotides (deoxyribose 3’ and 5’)
6. Triplicate code? 3 bases code for an amino
acid
RNA
• RNA is ribonucleic acid.
• It provides a bridge between DNA and
protein synthesis.
• Like DNA, RNA is also
made up of nucleotides.
What is a nucleotide?
• However the
nucleotides in RNA are
slightly different! Spot
the differences .....
• RNA is also a nucleic acid
– different sugar (ribose – still pentose)
– U (uracil) instead of T
– Single strand, usually
Nitrogenous base
(A, G, C, or U)
Phosphate
group
Uracil (U)
Sugar
(ribose)
RNA
The three types of RNA are:
– messenger RNA (mRNA)
– ribosomal RNA (rRNA)
– transfer RNA (tRNA)
mRNA is:
– Formed from the DNA in the nucleus.
– Small enough to fit through the pores in
the nuclear membrane.
mRNA comtinued ..
– Found in the nucleus and cytoplasm.
– A “bridge” molecule between DNA and
protein.
– Made by a process called transcription.
– Made of thousands of bases in 3s called
codons
– Transcribe the mRNA, and split into codons.
mRNA comtinued ..
– Found in the nucleus and cytoplasm.
– A “bridge” molecule between DNA and
protein.
– Made by a process called transcription.
– Made of thousands of bases in 3s called
codons
U GUACU GUGC UG
rRNA
– Make up ribosomes with proteins.
– Made in nucleolus of nucleus and passed out
into cytoplasm via the nuclear pores.
– Remain as free ribosomes or attached to
endoplasmic reticulum.
tRNA
–
–
–
–
Found only in the cytoplasm.
Only 3 bases exposed in 3D structure
General structure of “cloverleaf”
Made of two ends• 1 is the anti-codon which binds to a
specific mRNA codon.
• 1 is the amino acid binding site.
tRNA
– Specific to an amino acid.
– Degenerative code (as more
than one codon for an amino
acid)
Amino acids – all similar structure with an amino
group and a carboxyl acid group, “R” group changes
Genetic Code
1st base
U
UUU Phe
U
UUC Phe
UUA Leu
UUG Leu
CUU Leu
C
CUC Leu
CUA Leu
CUG Leu
AUU Ile
A
AUC Ile
AUA Ile
AUG Met*
GUU Val
G
GUC Val
GUA Val
GUG Val
*Met and initiation.
2nd base
C
UCU Ser
UCC Ser
UCA Ser
UCG Ser
CCU Pro
CCC Pro
CCA Pro
CCG Pro
ACU Thr
ACC Thr
ACA Thr
ACG Thr
GCU Ala
GCC Ala
GCA Ala
GCG Ala
A
UAU Tyr
UAC Tyr
UAA Stop
UAG Stop
CAU His
CAC His
CAA Gln
CAG Gln
AAU Asn
AAC Asn
AAA Lys
AAG Lys
GAU Asp
GAC Asp
GAA Glu
GAG Glu
3rd base
G
UGU Cys
UGC Cys
UGA Stop
UGG Trp
CGU Arg
CGC Arg
CGA Arg
CGG Arg
AGU Ser
AGC Ser
AGA Arg
AGG Arg
GGU Gly
GGC Gly
GGA Gly
GGG Gly
U
C
A
G
U
C
A
G
U
C
A
G
U
C
A
G
RNA SUMMARY
• 3 types; mRNA (messenger), rRNA
(ribosomal) and tRNA (transfer)
• mRNA; carries a copy of the DNA code from
the nucleus to the ribosome in the cytoplasm
• rRNA; formed at the ribosome alongside
protein
• tRNA; carries an amino acid to the ribosome
in the cytoplasm
Gene 1
Gene 3
Process to protein ....
DNA molecule
Gene 2
DNA strand
TRANSCRIPTION
RNA
Codon
TRANSLATION
Polypeptide
Amino acid
Transcription
• Watch these videos and
place the statements in
order ....
Higher education Scotland
Crash course 2.21-7.04.
McGraw Hill
DNALC
Transcription produces genetic
messages in the form of mRNA
RNA nucleotide
RNA
polymerase
3’
5’
3’
5’
Direction of
transcription
Template
strand of DNA
Newly made RNA
DNA vs RNA
• Compare the 2 nucleic acid types.
RNA vs. DNA
• RNA contains the sugar ribose; DNA
contains deoxyribose.
• RNA contains the base uracil; DNA contains
thymine instead.
• RNA is usually single stranded; DNA is
usually double stranded.
• RNA is short: one gene long at most; DNA is
long, containing many genes.
RNA vs. DNA
RNA
1. Complete the following table to compare RNA
and DNA
RNA
DNA
Number of strands
1
2
Found in…..
Nucleus & cytoplasm
Nucleus only
Sugar present
ribose
deoxyribose
Organic bases
G, C, A & URACIL
G, C, A & T
Number of types
3
1
Length of strand
Short
Long
Transcription Test
1. How many bases in the genetic code
correspond with an amino acid?
2. Draw the section of the mRNA strand that
would be transcribed from section X on the
DNA shown.
A T G G G C A T A C
T A C C C G T A T G
3. Which enzyme would direct this process?
4. What is the difference between an intron and
an exon?
5. What happens to primary transcript of mRNA?
6. What is the name of this process?
Transcription Test
1.
2.
3.
4.
3, triplicate code
Top one, 3’ to 5’ U A C C C G U A U G
RNA polymerase
Exon is expressed as it is the coding region,
intron is non-coding region – polypeptide is
fragmented
5. From primary transcript Introns are removed
and exons are spliced together to form
mature mRNA
6. RNA splicing
Remember RNA? or ID badges
1. How many types?
2. Location?
3. What are each of their structures (and label
within) and functions?
4. Any specific names gives? Lengths?
Remembering RNA ...
http://www.mfpl.ac.at/rna-biology/rna-history/
RNA
mRNA
tRNA
rRNA
Location
Nucleus and
cytoplasm
Cytoplasm
Ribosome
Lengths
Longer
3 bases exposed
N/A
Structure
Codon (from
DNA template),
made up of
introns/exons
(exons spliced for
mature mRNA
Cloverleaf, 1
leaf Anticodon
(against mRNA),
stalk is amino
acid
Part of ribosome
with protein
Learning Outcomes
• Review the process of transcription
• Describe the process of translation
DNA
molecule
Gene
1
Gene 3
Gene 2
DNA strand
TRANSCRIPTION
RNA
Codon
TRANSLATION
Polypeptide
Amino acid
Translation
Occurs in cytoplasm (mature mRNA transcript
through nuclear pore) on the ribosome
(enzymes needed for protein synthesis).
5’
3’
• Site E; releases (discharges)
tRNA after amino acid (aa) part
of polypeptide
• Site P – next tRNA held by H
bond to mRNA
• Site A – holds next tRNA with
its aa then peptide linked to
previous aa (P)
Translation .....
Translation
• Occurs in cytoplasm (mature mRNA
transcript through nuclear pore) on the
ribosome.
Translation
1. A ribosome attaches to
the mRNA at an initiation
codon
(AUG).
The
ribosome encloses two
codons.
2. met-tRNA diffuses to
the ribosome and attaches
to the mRNA initiation
codon by complementary
base pairing
3.The next amino acid-tRNA
attaches to the adjacent mRNA
codon (leu in this case) - The
codon and anticodon bases
matching up
4. The bond between the amino acid
and the tRNA is cut and a peptide
bond is formed between the two
amino acids.
5 The ribosome moves along one
codon so that a new amino acidtRNA can attach. The free tRNA
molecule leaves to collect
another amino acid. The cycle
repeats from step
6. The polypeptide chain elongates one
amino acid at a time, and peels away from
the ribosome, folding up into a protein as it
goes. This continues for hundreds of amino
acids until a stop codon is reached, when
the ribosome falls apart, releasing the
finished protein.
Steps in translation SUMMARY
1. Initiation – needs start codon (AUG, for
methionine) in P site with anti codon?
2. Elongation – complementary tRNA bring correct
amino acids which are added through a peptide
bond
3. Termination
A stop codon (AUU,
AUC or UGA) which has
a release factor which
frees the polypeptide
from ribosome.
Translation
• Multiple translation can occur with many
ribosomes reading the same mRNA – the
ribosomes on the same mRNA are called polysomes or polyribosome
• Translation requires ATP!
What’s happening?
Now explain the WHOLE process
Animate/Model/Demonstrate
• Can you animate it?
• Anyway possible – here is my original ......