Download Chapter 10: Nucleic Acids and Protein Synthesis

Chapter 10: Nucleic Acids
and Protein Synthesis
DNA
• DNA (Deoxyribonucleic acid)
– Stores and transmits genetic information
– Double stranded molecule (looks like a spiral
staircase or twisted rope ladder)
DNA Structure
• Double helical nature discovered in 1953
by Watson and Crick
• DNA is made of two strands of nucleotides
that wrap around each other to form a
double spiral or double helix
DNA Structure
• DNA is made of nucleotide sub-units
3 Parts of DNA nucleotide
a. Deoxyribose (pentose sugar)
b. Phosphate group
c. Nitrogenous bases (A,T,G,C)
Nitrogenous Bases in DNA
• Adenine (A) pairs with Thymine (T)
• Guanine (G) pairs with Cytosine (C)
• Adenine and Guanine are purines- these
are 2-ringed bases
• Thymine and Cytosine are pyrimidinesthey are 1-ringed bases
Nitrogenous Bases
• The nitrogenous bases make up the
“rungs” of the DNA ladder
• The bases are held together by Hydrogen
bonds
DNA Replication
• Process of making a copy of the DNA
Steps of DNA replication (Possible essay)
1. Helicase enzymes separate two strands
of nucleotides (break the H-bonds that
hold bases together)
-the point at which the 2 strands of DNA
separate is called the replication fork
2. Another enzyme (DNA polymerase)
binds to separated strands and starts
moving along originalDNA
3. DNA polymerase assembles a
complementary strand from free
nucleotides that are found in the
nucleoplasm
4. Nucleotides are joined to new chain by
covalent bonds b/t phosphate group and
deoxyribose sugar and are joined to
original DNA strand by H-bonds
Ex: Original DNA sequence: ATTCCG
DNA polymerase builds new strand that is
complementary or TAAGGC
Replication Summary
• Replication does not begin on one end and
move to other
• Instead, it starts and occurs simultaneously at
different sites along DNA molecule (Ex:
replication occurs at 6,000 different sites in fruit
fly DNA)
• Allows for faster replication
• End result of replication- 2 identical DNA
molecules, each consisting of one new strand
and one from original DNA molecule
Accuracy of Replication
• Replication is very accurate (1 error per
every 10,000 nucleotides)
• Errors in DNA are called mutations
• These changes in DNA sequence can
have serious effects
• Enzymes proofread nucleotide sequence
reducing error rate to 1 per 1 billion
nucleotides
Other Agents that Damage DNA
• Chemicals
• Radiation (i.e. UV from sunlight)
These can lead to mutations that could
result in cancer
RNA
• RNA (Ribonucleic
acid)
• Responsible for
moving genetic info.
from DNA in the
nucleus to the site of
protein synthesis in
cytosol
RNA Structure
• Similar to DNA in that both are made of
nucleotide sub-units
Parts of an RNA nucleotide:
a. Ribose (sugar)
b. Phosphate group
c. Nitrogenous base
Differences between DNA & RNA
DNA
1. Sugar is Deoxyribose
2. Double-stranded
molecule
3. Bases include: A, T,
G, and C
RNA
1. Sugar is Ribose
2. Single-stranded
molecule
3. No T, replaced with
Uracil (U)—Uracil is
a pyrimidine
Types of RNA
1. Messenger RNA (mRNA)
-single, uncoiled strand of RNA
nucleotides
*Carries the genetic info. from DNA in
nucleus to cytosol of cell
RNA types (continued)
2. Transfer RNA (tRNA)
-single chain of about 80 nucleotides
-hairpin shape that binds to specific
amino acids– helps form polypeptide
chains
RNA types (continued)
3. Ribosomal RNA (rRNA)
-RNA nucleotides in a globular form, joined
by proteins makes up ribosomes
-most abundant type of RNA
Ribosomes are site of protein synthesis
Transcription
-Process by which genetic information from
DNA is copied to RNA
http://www-class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a2.html
(Possible Essay)
Steps of Transcription
1. RNA polymerase binds to specific region
of DNA called a promoter (beginning of
DNA strand that will be transcribed)
-once the RNA polymerase bonds to the
promoter, DNA will separate
-one strand of DNA will be used for
transcription
Transcription
2. RNA polymerase bonds to first DNA
nucleotide of template strand
-begins adding complementary RNA
nucleotides to newly forming RNA
molecule
-follows complementary base pairing
rules except Uracil pairs with Adenine
Transcription
3. RNA polymerase keeps adding
nucleotides to RNA strand until it reaches
a DNA region called the termination
signal
-once termination signal is reached, RNA
polymerase releases DNA and newly
formed RNA molecule
Transcription
• DNA strands will rejoin and the mRNA will
leave the nucleus via a nuclear pore and
head to the cytoplasm where it can direct
protein synthesis
• All 3 types of RNA are made via
transcription and all 3 will play a role in
protein synthesis
Protein Synthesis
• Proteins are made of amino acid sub-units
linked together by covalent peptide bonds
• 20 different amino acids
• Sequence of amino acids determines the
type of protein that will be made
• Function of protein depends on structure
The Genetic Code
• Sets of 3 nucleotides in an mRNA strand
that code for amino acid sequence in a
protein
• Every 3 nucleotides in mRNA is called a
codon
• Each codon codes for a specific amino
acid
The Genetic Code
• There are 64 codons
• AUG is start codon (methionine) signals
ribosome to start translating mRNA
molecule
• 3 Stop codons:
UAA
UAG
UGA
Translation
• Process of assembling proteins from
information encoded in mRNA
• Happens on ribosomes
• Ribosomes attached to E.R. make
membrane proteins and proteins that will
be exported (i.e. insulin)
• Ribosomes in cytoplasm make proteins
that are used within cell
Translation
• Shape of tRNA impacts function
• Anticodons of tRNA are complementary to
mRNA codons
Translation
• Pairing of anticodons of tRNA with mRNA
codons ensures that amino acids are
added in the correct order
Steps of Translation
1. Ribosome attaches to start codon (AUG)
on mRNA strand--Start codon pairs with
anticodon (UAC) of a tRNA
2. Ribosome continues to move along
mRNA and each codon pairs with a
corresponding anticodon of tRNA
Translation
3. Ribosome keeps moving along mRNA
strand until a stop codon is reached