Download Chapter 10 DNA Replication and Expression

Chromosome Abnormalities
• Non-disjunction during meiosis can cause a
gamete to have an extra chromosome
• Trisomy = three copies of the same
chromosome.
• Most are lethal before birth, but three of
chromosome 21 causes Down syndrome.
Trisomy of Chromosome 21
Chapter 10 DNA Replication and
Expression
DNA (Deoxyribose Nucleic Acid)
• Polymer made of subunits called nucleotides
• Nucleotides have three parts
– Phosphate
– Sugar (deoxyribose)
– Nitrogen bases
Four Nitrogen bases of DNA (9.1)
•
•
•
•
Adenine
Guanine
Cytosine
Thymine
DNA structure (Fig. 10-2)
• Double helix
– James Watson and Francis Crick (Nobel Prize)
– Two strands held together by hydrogen bonds
• Bases are paired up:
– Adenine to Thymine
– Cytosine to Guanine
• DNA is twisted (helix)
X Ray Crystallography of DNA (10.3)
DNA inside a Eukaryote
• DNA wraps around proteins (histones) to form
chromatin.
• Chromatin coils up into chromosomes.
DNA is Replicated
• Parent DNA strands act as templates for new
DNA
• Strands separate and new bases are added to
each side
DNA replication (10.6)
DNA replication requires three enzymes (10.7)
• Helicase
• DNA polymerase
• Ligase
DNA Expression
Central Dogma of Molecular
Biology: DNA  RNA  Protein
Flow of Genetic Information (10.8)
What is RNA?
• Ribose Nucleic Acid
• Nucleic acid similar to DNA
• Three important differences
– Single strand
– Sugar is Ribose
– Uracil instead of Thymine
DNA contains information used to make
proteins
• 95% of DNA sequence is meaningless or
“junk”
• 5% that has information is contained in genes
• Gene is a sequence of DNA that codes for a
protein
DNA to Protein (10.10)
How a gene produces a protein
• Genes are TRANSCRIBED into messenger RNA
• mRNA goes to ribosomes for protein synthesis
• Transfer RNA carries Amino Acids to be
assembled at the ribosomes
• mRNA is TRANSLATED into proteins.
Transcription 10.13
Transfer RNA
So how do we know what the amino acid order
will be?
A gene sequence is divide into groups of three
(codons)
Codons on mRNA are recognized by tRNA
Each codon codes for an amino acid
How are codons read? (10.10)
Viral genetics
What about viruses?
• Viruses are nucleic acids surrounded by a
protein capsule.
• Viruses invade host cells by injecting their
DNA
• Viral DNA incorporates into the host cell’s
genome ( Lysogenic Phase)
• Viruses use their DNA to force host cells to
produce more viruses ( Lytic Phase)
• Viruses do not fit into the cell theory.
Phage Virus Cycles (10.26)
Mutations
• Mistakes in copying of DNA
• Three types
– Insertion
– Deletion
– Substitution
Consequences of mutations
• Most mutations are neutral – no noticeable
effect on the protein
• Some mutations are deleterious
– Genetic disorders
– Cancer
• Some mutations may produce a “good” trait
• In both cases a change in the bases changes
sequence of amino acids