DNA STRUCTURE AND FUNCTION CHAPTER 10. DNA STRUCTURE.
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Transcript of DNA STRUCTURE AND FUNCTION CHAPTER 10. DNA STRUCTURE.
1. DNA: a. Nucleic acid which is a polymer of monomers
called nucleotides. b. Nucleotide made of: Phosphate group,
sugar (deoxyribose: 5 carbon atom molecule) and nitrogenous base.
DNA STRUCTURE
c. Nitrogenous bases: A (Adenine), T(thymine), G (Guanine), and C(cytosine). Specific DNA information is stored according to the nitrogenous bases arrangement.
1. Cont. DNA:
i. Cont. Nitrogenous bases: ii. Two kinds :
1. Pyrimidines: C and T 2. Purines: A and G 3. In a DNA molecule, a pyrimidine binds by
hydrogen bond to a purine.
1. Cont. DNA:
d. DNA is a double stranded helix, and has a backbone of sugar-phosphate and the N bases are arranged as appendages along this back bone.
e. The two DNA strands are antiparallel to each other (oriented in opposite directions).
1. Cont. DNA:
2. RNA a. Nucleic acid which is a polymer of monomers
called nucleotides. b. Nitrogenous bases: Same as DNA except
T(Thymine) is changed for Uracyl (U) c. Sugar: Ribose instead of deoxyribose d. One strand.
3. DNA replication: a. Starts at “origin of replication”, where DNA is
uncoiled by a gyrase.
DNA FUNCTION
3. DNA replication: a. Initiation proteins bind to origin and both DNA strands
open like a zipper, and two new daughter strands are synthesized by the enzyme DNA polymerase.
b. Both parental strands are used as templates (leading and lagging strands).
e. Replication is bidirectional, and two replication forks are formed moving in different directions.
3. Cont. DNA replication:
f. DNA polymerases catalyze the insertion of free nucleotides complementary to the parental DNA strand: semiconservative replication.
g. Lagging strand: Okazaki fragments. h. ATTAGGACCATTAGGACC Parental strand
TAATCCTGGTAATCCTGG Daughter strand
3. Cont. DNA replication:
DNA REPLICATION
THE SEQUENCE
DNA POLYMERASE
4. Transcription: DNA → RNA
4. Transcription: DNA > RNA a. Types of RNA:
i. mRNA( Messenger RNA):Carries the message of DNA (has the message for a specific protein)
ii. r RNA (Ribosomal RNA): Form part of ribosomes.
iii. tRNA: (Transfer RNA):Amino acid carrier
b. Process of transcription: i. DNA serves as template for RNA
synthesis. ii. Unzipping of DNA; RNA polymerase
recognizes promoter, binds to it and bring new nucleotides for new RNA strand complementary to the parental DNA template.
ATTAGGACCATT Parental DNA strand UAAUCCUGGUAA Daughter RNA strand
U instead of T
b. Process of transcription:
TRANSCRIPTION
THE PROCESS
SENSE STRAND
ANTI-SENSE STRAND
Notes: 1. mRNA: Messenger RNA
a. Carries the message from DNA b. Has CODONS (Triplets of nucleotides)
Ie AUG, AGC, GAA c. Each codon specifies an amino acid
2. tRNA: Transfer RNA a. Clover leaf form b. Carries the anticodon c. On the opposite side, tRNA carries a
Specific aminoacid d. Each Anticodon binds to the codon of
mRNA bringing the corresponding amino acid
e. Redundancy of the genetic code: f. Starting codon: AUG g. Stop codons: UGA, UAG, UAA
Notes: 1. mRNA: Messenger RNA
a. Carries the message from DNA b. Has CODONS (Triplets of nucleotides)
Ie AUG, AGC, GAA c. Each codon specifies an amino acid
2. tRNA: Transfer RNA a. Clover leaf form b. Carries the anticodon c. On the opposite side, tRNA carries a
Specific aminoacid d. Each Anticodon binds to the codon of
mRNA bringing the corresponding amino acid
e. Redundancy of the genetic code: f. Starting codon: AUG g. Stop codons: UGA, UAG, UAA
iii. Eukaryotic RNA is processed before leaving the nucleus. It is cut by some proteins and RNA. Sometimes the RNA transcript itself catalyses the process. It cuts genes that do not encode for proteins (introns).
4. Translation: mRNA → Proteins a. Flow of genetic information: CENTRAL DOGMA
DNA → mRNA → Proteins
REVERSE TRANSCRIPTASE ( HIV)
b. Translation occurs in three stages: i. Chain initiation: Ribosomes recognize
initiation codon: AUG. tRNA with UAC anticodon brings amino acid (Met) and bind.
ii. Chain elongation: Next codon of mRNA is read by ribosome UUA and tRNA brings Leu. Met and Leu are attached by an enzyme, and first tRNA breaks free. Ribosome moves and reads next codon; t RNA brings respective amino acid. This process is repeated, and protein chain grows.
Cont. Translation
iii. Chain termination: Terminator codon is reached. (UGA,UAA,UAG)
TRANSLATION
THE PROCESS
U
Met
A C
U
Met
A C A
Leu
A U
U
A C A
Leu
A U
Met
U
A C A
Leu
A U
Met
GG
U
A
Leu
A UC
Gly
AC
Met
A
A UC
Gly
AC
Leu
Met
AG
A
U C U
Arg
C
AC
Met
Leu
Gly
U C U
Arg
Met
Gly
Leu
5. Mutations: Change in DNA that will imply a change in mRNA and proteins. A change in a nucleotide can mean a big change in a protein molecule that no longer can serve its purpose.
Mutations can be:
i. Spontaneous: Occur naturally, every 106 to 1010 divisions.
ii. Induced: Physical and chemical agents are involved called mutagens.
ii. Cont. Induced mutations:
1. Physical agents that produce mutations: a. Ultraviolet light (UV): Causes thymine
dimmers: ATTCGGG → UAAGCCC (NORMAL)
ATTCGGG → UV light → AT=TCGGG Cannot be rea
ii. Cont. Induced mutations:
1. Physical agents: a. Ultraviolet light (UV): Causes thymine
dimmers: ATTCGGG → UAAGCCC (NORMAL)
ATTCGGG → UV light → AT=TCGGG → Cannot be read
b. X Rays and Gamma rays: Bombard electrons in DNA, causing changes.
1. Cont. Physical agents that produce mutations:
a. Base analogs: Mimic nitrogenous bases, and take their place. DNA malfunctions.
ATTCGGG → Add T* → AT*T* CGGG → can’t
be read
2. Chemical Agents that produce mutations:
Binds GBinds A
AAAGGGCCCTG
T*T*T*CCCGGGAC
GGGGGGCCCTG
c. Kinds of mutations: i. Affect one nitrogenous base in DNA. Can be
substitution, addition, and deletion 1. Base substitution:
TTAACC → substitution by G → TTAGCC
↓ ↓
AAUUGG AAUCGG
↓ ↓ ↓ ↓
Asn Trp Asn Arg
DNA
RNA
PROTEIN
2. Base deletion and addition: Causes frameshift mutations. THE FAT CAT EAT THE RAT
↓ deletion of F
THE ATC ATE ATT HER AT: Frameshift
A piece of chr A broken pi
MUTATIONS MAY INVOLVE LARGER SEGMENTS OF DNA
6. Repair mechanism: To correct mistakes in DNA.
a. Mismatch repair: Proofreading by DNA polymerase. b. Excision repair: Nucleases excise thymine dimmers.
7. Transposable genetic elements: i. Insertion sequences: Carry no genetic
information. Only insert and make copies of them.
ii. Transposons: Jumping genes. Carry R genes.
Insertion sequence
8. Microbial genetics: i. Viruses :
1. Are made of a protein coat and nucleic acid. Either DNA or RNA.
2. Viruses infect animal cells, plant cells and bacteria ( Bacteriophages)
Cell Size and Scale Resource at the University of Utah.
i. Cont.Viruses :
3. When bacteriophages infect a bacterium, they can go two ways:
a. Lytic cycle: Lyses or break the cell by entering and taking up the cell synthetic machinery to reproduce itself.
Cont. Microbial genetics: b. Lysogenic cycle: Instead of lysing the
cell, the DNA of the virus inserts in the cell DNA and can be passed on from parent cells to daughter cells. Sometimes those genes confer toxic genes.
ii. Bacteria and Genetic Engineering What are PLASMIDS?
Extra chromosomal circular pieces of DNA in bacteria that normally carry genes such as:R genes : Resistance to antibiotic genes, TOX genes: Toxic genes (poisons)F Factors : Fertility factors (Sex factors) Plasmids are the vehicles of Genetic Engineering
1. Genetic recombination: Transfer of DNA (plasmid DNA or chromosomal DNA fragments) from donor to recipient cell forming a new combination of genes
a. Forms of genetic recombination: i. Transformation: A metabolic active
bacteria acquires a piece of “naked” DNA (from a dead bacteria) from the environment.
ii. Conjugation: Transfer of DNA form one bacteria (male) to another (female) by means of a sex pilus.
1. Needs cell to cell contact 2. Mediated by plasmids.
iii.Transduction: DNA is transferred from one bacterium to another by means of a virus or bacteriophage.
2. Recombinant DNA technology: a. Techniques to combine genes from
different sources into a single DNA molecule that is used for practical purposes
b. Bacteria are used, especially E. coli.
c. Genetic engineering: 1. The use of microbial DNA to manipulate or control gene expression. 2. Biotechnology: Industrial and commercial applications of genetic engineering
3. Construction of a recombinant DNA molecule: