Download Inheritance and the Structure of DNA

Inheritance and the Structure of DNA
Deoxyribonucleic Acid
DNA Discovery Timeline
• 1928-Frederick Griffith
– transforming factor (material carrying genetic info)
• 1944-James Watson and Francis Crick
– discovered that DNA was the transforming factor
• 1952-Rosalind Franklin and Maurice Wilkins
– took x-ray photographs of the DNA molecule
• 1953-Watson and Crick
– created a three-dimensional 3-D model of DNA
• 1962-Watson, Crick, and Wilkins
– received the Nobel Prize in Medicine
What is DNA?
• Genetic material used to express traits
• Nucleotide units
– Deoxyribose (sugar)
– Phosphate
– Base
• Purines (double ring)
– Thymine ( T )
– Cytosine ( C )
• Pyrimidine (one ring)
– Adenine ( A )
– Guanine ( G )
Complementary Strands
• Order of bases on the nucleotides in one strand of DNA
complements the order of bases on the opposite strand
– Anti - parallel
• 5’ -> 3’
• Refers to where sugar & phosphate attach
• Direction which new DNA is made
– Sugar and phosphate alternate
• Make up the sides
– base sequence (ATGC)
• attach to sugar
DNA Replication/Synthesis pg200
• DNA stores and transmit information
– tells cells which proteins to make and when to
make them
• DNA located in the nucleus and cannot leave.
• Replication is duplication or making more of
DNA
– Occurs during S phase of interphase
• 2 main enzymes involved DNA Helicase and
DNA Polymerase
DNA Helicase and DNA Polymerase
1. Helicase unzips the DNA by
breaking the hydrogen bonds
between the two strands
2. Binding proteins stabilize the
strands keeping them open
3. Nucleotide units are added
from a 3’->5’direction(5’->3’
new complementary strand
direction), this leading edge
is continuous
4. On the other strand of DNA, the 2nd strand called the lagging
strand)
• nucleotides are added from the 5’ end; creating a
complementary strand of 3’->5’sporadically
• since polymerase moves in a 5’->3’ it will move around to find
location on the original strand that it can match up with to
create segments on the new complementary DNA
• this leaves gaps (called Okazaki fragments) that are later filled
by the enzyme ligase
5. DNA Polymerase proof reads each strand sealing the molecules
RNA (Ribonucleic Acid)
• RNA differs from DNA
– Sugar is ribose
– The nitrogen base THYMINE is replaced by URACIL
• RNA U bonds with DNA A
– RNA is single-stranded
• There are three types of RNA
– Messenger RNA (mRNA)
– Transfer RNA (tRNA)
– Ribosomal RNA (rRNA)
RNA (created from DNA)
• Messenger RNA (mRNA)
– copies the information from the DNA in the
nucleus
• Transfer RNA (tRNA)
– reads the information from mRNA
– carries amino acids to the ribosome
• Ribosomal RNA (rRNA)
– Links up with mRNA to read the “message” from
DNA and to reveal codons for tRNA
Transcription vs Translation pg 206
• Transcription
– DNA information to mRNA, tRNA, rRNA
– Occurs in nucleus
• Translation
– mRNA to tRNA and rRNA
• Polypeptide bonds are created between amino acids
• Twist and turn of these chains create specific proteins
• Result in phenotypes of organisms
– in cytoplasm
Transcription pg 206
• Reading the gene
• occurs on only one strand
of DNA
• RNA polymerase
• Transcribed information
has created a
complementary strand of
mRNA from DNA
• A=U, C=G
Transcription illustration
Transcription
1. RNA polymerase, binds to the promotor
• Promoter is particular sequence of DNA that RNA
polymerase binds
• DNA molecule unwinds and strands separate
2. RNA polymerase adds free nucleotides on one
of the DNA strands
•
•
Complementary bases (AUGC)
As polymerase moves over DNA the strands rewind
3. RNA polymerase reaches termination signal
indicated by sequence of bases
•
Releases DNA and RNA (mRNA,tRNA,rRNA)
Transcription
Genetic Code pg 207
• Gene Expression
– Amino acids are created from instructions
found in the nucleotide sequence on mRNA
• Genetic Code term used to describe how the
sequence of nucleotide units (bases)
corresponds to a particular amino acid
–Three letter (bases) word is referred to as a
codon
–mRNA has the codon
Codons in mRNA
• Each sequence of 3 bases on mRNA encodes for
either an amino acid or stop/start signal
• Some amino acids will have 1,2,or 3 different codons
– No codon codes for more than one amino acid
– 64 mRNA codons
• There are special codons that act as start and stop to the sequence
• For example, AUG acts as a start codon codes for the amino acid
Methionine
• Others like (UAA, UAG, or UGA) are stop codons that don’t code
for amino acids but are the end of the translating sequence
• Reading the mRNA table pg 207, let’s try a few
Translation
• RNA molecules (tRNA, rRNA, and mRNA) take
information from DNA to proteins
• Translates the sequence of bases found in the
gene into material that the body can “read”
(visible traits)
• Occurs in Cytoplasm
RNA molecules
How it comes together in cytoplasm
Translation pg207
• Revisit Protein structure pg 208
– Polypeptides
– 20 different types amino acids
– Twist and fold into 3-D structure
• Shape critical for function
Steps of Translation
1. rRNA, mRNA, and tRNA join together
•
•
•
Enzyme attaches amino acid to one end of tRNA
Other end of tRNA (anticodon) attaches to
complementary bases on mRNA
AUG (methionine) begins the sequence
2. mRNA continues to “read” mRNA codons
•
•
•
•
tRNA brings the appropriate amino acids
Starting from the 1st codon, tRNA brings in the start
amino acid (methionine)
Then as the 2nd tRNA attaches it’s amino acid to the 1st
amino acid (creating a peptide bond) the 1st tRNA leaves
This process continues until the stop codon is reached
Textbook pg 208
Initiation and Elongation
3. Polypeptide chain continues to grow as the
rRNA “reads” the codons on mRNA
4. rRNA reaches the stop codon (UAA, UAG, or
UGA)
•
New polypeptide chain is released
5. The components of translation come apart
Elongation, Termination, Disassembly
Another view of Protein Synthesis
FYI - Deoxyribose vs Ribose sugars
• 2-Deoxy-Ribose in DNA is replaced by Ribose in RNA.
• The difference is a hydroxy group ( -OH ) in RNA versus a
single proton ( -H ) in DNA.
• The extra -O- in the ribose backbone prevents formation of
stable double-helices in RNA.