Chapter 21-Nucleic Acids An Protein Synthesis Flashcards
Types of Nucleic acids
Deoxyribonucleic (DNA) and ribonucleic (RNA)
Nucleotides
Unbranched polymers of repeating monomer units
Ex: DNA and RNA
How many nucleotides does a DNA molecule contain?
Several million
Three components of a nucleotide.
Base, five-carbon sugar, and a phosphate.
Phosphoryl group
When -PO3(2-) is part of a larger molecule
Base- in Nucleic acids
Derivatives of pyramidine or purine
Purine bases with double rings (DNA)
Adenine (A) and guinine (G)
Pyrimidine bases with with single rings (DNA)
Cytosine (C) and thymine (T)
RNA bases
Adenine(A), guanine (G) and cytosine (C) but thymine is replaced with uracil (U)
Five-carbon sugar (RNA)
Ribose (r-in RNA)
Atoms in pentose sugars
Numbered with primes (1’, 2’,3’,4’, and 5’)
-used to differentiate them from atoms in the bases
Five-carbon sugar (DNA)
Deoxyribose (d in DNA)
- similar to ribose except there is no hydroxyl group on c2’
- deoxy means “without oxygen”
How is a nucleoside produced?
When a pyrimidine or a purine forms a glycosidic bond to C1’ of a sugar (either a ribose or a deoxyribose)
Example: adenine, a purine, and ribose form a nucleoside called adenosine
How is a nucleotide produced?
When the C5’ -OH group of ribose or deoxyribose in a nucleoside forms a phosphate ester.
5’ monophosphate nucleotides
Found in DNA and RNA.
Naming nucleosides
Nucleoside that contains a purine- ends with -osine
Nucleoside that contains a pyrimidine- ends with -idine
Corresponding nucleotides in RNA and DNA are named by adding 5’-monophosphate.
Examples: adenosine-5’-monophosphate (amp)
ATP
Energy molecule in our bodies
Major source of energy for most energy-requiring activities in the cell
GMP+phosphate=GDP and GTP (energy source for protein synthesis)
dGMP+phosphate=dGDP and dGTP (intermediate in phospholipid synthesis)
Diphosphates
Phosphoryl group in any nucleoside can bond to one additional phosphate group (ADP) adenosine-5’-diphosphate
Triphosphate
Phosphoryl group in nucleoside-5’-monophosphate bonds to two additional phosphate groups to form a triphosphate. (adenosine-5’-triphosphate) ATP
Nucleic acids
Polymers of many nucleotides in which the 3’-hydroxyl group of the sugar in one nucleotide bonds to the 5’-carbon atom in the sugar of the next nucleotide.
Phosphidiester bond
The link between the sugars in adjacent nucleotides
Primary structure
Each Nucleic acid has its own unique sequence of bases.
Nucleic acid sequence
Read from sugar with free 5’-phosphate to the sugar with free 3’-hydroxyl group.
Example: nucleotide sequence starting with adenine (free 5’-phosphate end) in the section of RNA 5’-A-C-G-U-3
Specific relationship between bases
The amount of adenine (A) is equal to the amount of thymine (T), and the amount of guanine (G) is equal to the amount of (C) cytosine.
Chargoff’s rules
Number of purine molecules=number of pyrimidine molecules
A=T
G=C
Double helix
Consists of two polynucleotide strands winding about each other like a spiral staircase
complimentary base pairs
A-T- form one hydrogen bond
G-C- form three hydrogen bonds
each of bases along a polynucleotide strand forms hydrogen bonds to a specific base on the opposite DNA strand
replication
strands in the parent DNA molecule separate, which allows the synthesis of complimentary strands of DNA.
Replication process
Stars when an enzyme called helicase catalyzes the unwinding of a portion of the double helix by breaking the hydrogen bonds between the complimentary bases.
These strands are now templates for the synthesis of new complementary strands of DNA.
DNA Polymerase
Catalyzes the formation of phosphodiester bonds between the nucleotides.
Hydrolysis of pyrophosphate
Releases energy for the new bonds
Semi-conservative replication
Produces two new DNA’s called daughter DNA’s that are identical to each other and exact copies of the original parent DNA
Helicase
Unwinding of DNA that occurs simultaneously in several sections along the parent DNA molecule
Replication forks
DNA polymerase catalyzes the replication process at each of these open DNA sections
Catalyzes only phosphodiester bonds and must move in opposite directions alongside the separate strands on DNA.
Leading strand
The new DNA strand that grows in the 5’-3’ direction is synthesized continuously
Lagging strand
Synthesized in the opposite direction, which is in the reverse 3’-5’ direction
Okazaki fragments
Parts of lagging strand that are synthesized at the same time by several DNA polymerases and connected to form continuous strand by DNA ligases to give a sing 3’-5’ DNA strand.
What makes up most of the Nucleic acid found in the cell?
RNA
RNA
Involved in transmitting the genetic information needed to operate the cell
Unbranched polymers of nucleotides
Differences in RNA from DNA
- the sugar in RNA is ribose rather than deoxyribose found in DNA
- in RNA, the base uracil replaces thymine
- RNA molecules are single-stranded Nucleic acids
- RNA molecules are much smaller than DNA molecules
Three major types of RNA in the cells
Messenger RNA, ribosomal RNA, transfer RNA
Most abundant type of RNA?
Ribosomal RNA- 80% of RNA
How is ribosomal RNA combined?
With proteins in the ribosomes.
Ribosomes
The sites within the cells where protein synthesis occurs
How many sub units do ribosomes have?
2
A large subunit and a small subunit
Purpose of messenger RNA
carries information for protein synthesis from the DNA in the nucleus to the ribosomes
5% of RNA
Purpose is transfer DNA
Brings amino acids to the ribosomes for protein synthesis
15% of RNA
Structure of tRNA
70-90 nucleotides
Hydrogen bonds between complimentary bases produce loops that give SOME double stranded regions
Acceptor stem
3’ end with nucleotide sequence ACC
Anticodon
Series of three bases that complements three bases of an mRNA
Transcription
The genetic information for the synthesis of a protein is copied from a gene in DNA to make a messenger RNA
Translation
tRNA molecules convert the mRNA information into amino acids
Protein synthesis
DNA (transcription) mRNA (translation) protein
————–> ————->
Transcription: synthesis of mRNA
Transcription begins with section of DNA Molecule that contains the gene to unwind- mRNA forms bases that are complementary to DNA template. C &. G form pairS. T (in DNA) pairs with A (in mRNA), and A (in DNA) pairs with U ( in mRNA)
Exons
Code for proteins
Introns
Do not code for proteins
Pre-mRNA
Copy of entire DNA template ( including non coding introns)
Before Pre-mRNA leaves the nucleus
Introns must be removed
When does synthesis of mRNA occur?
When cells require a particular protein
NOT RANDOMLY
Where does the regulation of synthesis take place?
At the transcription level, where the absence or presence of end products determine which mRNA’s are needed for specific proteins
Enzyme induction
Occurs where high levels of a substrate turn on the transcription of the genes that produce the mRNA’s that code for specific enzymes
Operons
Sections of DNA that regulate the synthesis of related proteins
Control site
Each Operon has their own
Structural genes
Produce mRNA’s for specific proteins
Regulatory gene
In front of lactose operon that produces an mRNA for the synthesis of a repressor protein that blocks the synthesis of B-galactosidase by RNA polymerase
Genetic code
Three nucleotides (triplet) in mRNA called codon
Codon
Each one specifies an amino acids and it’s sequence in a protein
How many codons are possible?
64
Stop signals that code for the termination of protein synthesis
UGA, UAA, UAG
Anticodon
Loop which is a triplet of bases that complements a codon in an mRNA
Aminoacyl-tRNA synthetase
Enzyme that attached to the acceptor stem of each tRNA
When does activation take place?
When tRNA synthetase uses the anticodon of tRNA to form an ester bond between the carboxylate group of its amino acid and the hydroxyl group of the acceptor stem
What corrects incorrect combination?
Hydrolysis
Start codon
First codon in an mRNA
AUG
Chain elongation
Another tRNA carries a second amino acid to the adjacent codon of the mRNA
Translocation
First tRNA detaches from the ribosome
Ribosome shifts to the next codon of the mRNA
Polysome
Several ribosomes translate a single strand of mRNA simultaneously to produce several copies of the peptide chain at the same time
Release factors
Release the completes polypeptide chain from a ribosome
Mutation
Change in the nucleotide sequence of DNA
What causes mutation?
X-rays, overexposure to sun, chemicals called mutagens, and possibly some viruses
Somatic cell
Cell other than a reproductive cell
What can an uncontrolled growth cause?
Cancer
What if mutation occurs in a germ cell ( egg or sperm cell?)
DNA produces will have same genetic change
What happens when a mutation severely alters the function of a structural protein or enzyme?
The new cell may not survive or the person may exhibit a disease or condition that is a result of a genetic defect
Substitution mutation
The replacement of one base in the coding strand of DNA with another
Most common way in which mutations occur?
Substitution
Frameshift mutation
A base is added to or deleted from the normal order of bases in the coding strand of DNA
Genetic disease
When a protein deficiency is hereditary
Recombinant DNA
Cutting and recombining of DNA fragments
What is recombinant DNA used for?
To produce human insulin for diabetics
Antiviral substance interferon
Blood clotting factor VIII
Human growth hormone
What is most of the work in recombinant DNA done with?
Escherichia coli (e. coli)
Plasmids
Small circular molecules where bacterial cells exist
Easy to isolate and capable of replicatoon
Restriction enzyme
Breaks phosphodiester bonds in DNA between specific nucleotides
Used to cut open the circular DNA strands in plasmids
Human insulin
Treat diabetes
Erythropoietin (EPO)
Treat anemia; stimulate production of erythrocytes
Human growth hormone (HGH)
Stimulate growth
Interferon
Treat cancer and viral disease
Tumor necrosis factor (TNF)
Destroy tumor cells
Monoclonal antibodies
Transport drugs needed to treat cancer and transplant rejection
Epidermal growth factor ( EGF)
Stimulate helping of wounds and burns
Human blood clotting factor VIII
Treat hemophilia; allows blood to clot normally
Interleukins
Stimulate immune system
Prourokinase
Destroy blood clots; treat myocardial infractions
DNA fingerprinting
Restriction enzymes are used to cut DNA into smaller fragments called RFLP’s
RFLP
Restriction fragment length polymorphisms
Odds of two people who are not identical twins producing the same DNA fingerprint
One in a billion
Applications of DNA fingerprinting
Connecting suspects to a crime, determining biological parentage,establishing identity of a deceased person, matching recipients with organ donors
What is DNA used for.
Screening for genes responsible for sickle-cell anemia, cystic fibrosis, breast cancer, colon cancer, huntington’s disease, Lou gehrigs disease
Polymerase chain reaction (PCR)
Made it possible to produce multiple copies of (amplify) the DNA in a short time
Cloning
Viruses
Small particles of 3 to 200 genes that cannot replicate without a host cell
What do viruses contain?
DNA or RNA. But not both. DNA or RNA are inside a Protein coat
He does a viral infection begin?
When an enzyme in the protein coat of the virus makes a hole on the host cell, allowing the viral Nucleic acid to enter and mix with the materials in the host cell
Protease
Produces a protein coat to form a viral particle that leaves the cell
Vaccines
Inactive forms of viruses that boost the immune response by causing the body to produce antibodies to the virus
What childhood viruses can be prevented by using vaccines?
Polio, mumps, chicken pox, and measles
Retrovirus
Virus that contains RNA as its genetic material
What must a retrovirus first do inside the cell?
Reverse trancription
Reverse transcriptase
Uses the viral RNA template to synthesize complementary strands of DNA using the nucleotides present on the host cell
Provirus
Newly formed DNA that integrates with the DNA inside the host cell
