Download DNA Replication

DNA
Deoxyribose Nucleic Acid
DNA
•
DNA is a double helix.
•
A bonds to T: C bonds to G
•
In man, the DNA molecule ,
if fully extended, would
have a total length of 1.7
metres. If you unwrap all
the DNA you have in all your
cells, you could reach the
moon ...6000 times!
DNA
•DNA STRUCTURE
•DNA REPLICATION
Components of DNA
• NUCLEOTIDE
– Phosphate group-phosphodiester bond
– 5-Carbon sugar-deoxyribose
– nucleic acid (1 of the nucleic acids)
• Guanine-Purine
• Cytosine-Pyrimidines
• Adenine-Purine
• Thymine-Pyrimidines
• Held by hydrogen bonds
• One end of chain with free 5’ phosphate group
• Other end of chain with free 3’ hydroxyl group
• Adenine, thymine form two bonds
• Guanine, cytosine form three bonds
COMPONENTS
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DNA Replication
• DNA is opened by
enzymes (unzips)
helicase
• Complementary
nucleotides bond
with the old
strands• 2 strands created:
½ is the old strand;
½ is the new
strand.
DNA REPLICATION
• TAKES PLACE IN THE NUCLEUS
• END PRODUCT IS TWO IDENTICAL
STRANDS
• DURING CELL DIVISION- ONE STRAND
• FOR EACH CELL
• Replication occurs only in 5’(P) to 3’(OH)
direction(DNA IS READ 3’ to 5’)
• a. Replication of leading strand, 3' to 5' strand
• 1.
• 2.
New strand grows from 5' to 3’end
Elongates towards replication fork
REPLICATION
ENZYMES
Helicase
DNA polymerase
Topoisomerase
RNA primer
ligase
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From Genotype to Phenotype
• Protein synthesis--converting the genetic
code (in DNA) into proteins that the body
uses
• 3 Steps involved
– Transcription
– RNA splicing
– Translation
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DNA----RNA
• DNA
• RNA
• DOUBLE
STRANDED
• DEOXYRIBOSE
• NUCLEIC BASES
• SINGLE
STRANDED
• RIBOSE
• NUCLEIC BASES
–
–
–
–
THYMINE
GUANINE
ADENINE
CYTOSINE
–
–
–
–
URACIL
GUANINE
ADENINE
CYTOSINE
RNA
 Differences from DNA
– Single stranded (vs. Double stranded DNA)
– Contains uracil in place of thymine
– Ribose sugar (instead of deoxyribose)
 4 Types of RNA
preMRNA---transcribes the message from the
DNA(rough blueprint)
– mRNA (messenger RNA)-carries message to to
ribosome(final blueprint)
– rRNA (ribosomal RNA)--makes up the
ribosome(forman that assembles parts of protein
in a specific order)
– tRNA(transfer RNA)--carries amino acids to
ribosomes
tRNA
• Anticodon of MRNA
• Wobble to take in all
possible aa
combinations of 3
nitrogen bases
• Carries specific aa
on 3’ on of strand
DNA TRANSCRIPTION
DNA- GIVES CODE TO preRNA
or hnRNA
PROCESSING
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RIBOSOME
STRUCTURE
A site - attracts Trna
P site - forms peptide
bonds between aa of
protein
E site - where Trns leave
ribosome and aa chain
elongates
5’ end with initiator
sequence attaches to
small subunit
Large subunit goes over
small at the A site.
Attracts 1st Trna with aa
Met
DNA TRANSLATION
tRNA translates mRNA into proteins
SUMMARY
Comparison of DNA and RNA
• RNA is single
stranded
• RNA has uracil
instead of
thymine
• A-U
• DNA is double
stranded
• DNA has
thymine instead
of uracil
• A-T
Understanding DNA
• Inheritance/ Genetic Counseling
• Cell function/protein synthesis
• Embryonic development/gene
regulation
• Evolution/ phylogenetic
relationships
• Medicine/genetic diseases
• Genetic engineering/ recombinant
DNA
Changes in Chromosomes
• Mutation--a change in the sequence of DNA
nucleotides (nitrogen bases)
– Causes a change in the protein formed
– Causes a change in organisms’ phenotype (trait)
• Effects of mutations?
– Some have little or no effect
– A few are beneficial
– Most are harmful or lethal (fatal)
Chromosomal Mutations
• Deletion mutation--piece of chromosome breaks off and is
lost; the new DNA strands are also missing a piece
• Duplication--piece of chromosome breaks off and is
inserted on homologous chromosome
• Translocation--piece of chromosome breaks off and
attaches to a different, non-homologous chromosome
• Inversion--piece of chromosome breaks off, turns around
and reattaches in opposite direction
Mutations Illustrated
Gene mutations
• Frameshift mutation--deletion or addition of
single (or few) nucleotides alters the amino
acid sequence of the protein
• Point (Substitution) mutation--wrong base is
added in a position--new DNA chains will
show the change
Point Mutations
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MUTATIONS
Frameshift Mutations
Expansions are responsible for many
genetic diseases:
• Muscular Dystrophy (CTG repeats)
• Huntington’s (CAG repeats)
• Fragile X (CCG repeats)
Replication Errors and
Mutations
• Inheritance of mutations
– Harmful mutations
• Individuals may not live to reproductive age
• Individuals may not develop/adapt as well
– Advantageous mutations
• Help survival of organism and are passed down if
mutation occurred in cells that produce
gametes
Genes and cancer
• Cancer is uncontrolled, abnormal cell
division
– Apoptosis--programmed cell death, which
is necessary for normal functioning
• Cause of cancer?
– Genes that control production of new cells
don’t turn off
Genetic causes of cancer
• Oncogenes--cause cell to become
cancerous
• Genes become oncogenes in 3 ways
– Mutation can occur in a growth-factor gene,
causing rapid, uncontrolled cell growth
– Error in DNA replication, producing multiple
copies of a single-growth factor gene
– Change in gene’s location--falls under the
control of a different promoter is transcribed
more often (producing more growth-factor)
Tumor suppression
• Humans have tumor-suppressor genes which are
natural “anti-oncogenes”
– If tumor suppressor gene is mutated, uncontrolled
growth/reproduction occurs
• Retinoblastoma--inheritable cancer in eyes caused
by changes in tumor-suppressor gene on
chromosome 13
– Can also occur when mutations occur in an individual (not
always inherited)
• Identifying location of these genes can increase
identification and treatment of cancer