DNA Replication: copying DNA during cell division

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• DNA Replication copying DNA during cell
  division
• 2 general steps
• 1. Parent DNA (template) separates into 2
  strands (aided by DNA helicase)
• 2 new (daughter) DNA strand made
• a. Complementary to parent strands
• b. Get 2 DNA molecules that are same as parent

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Replication occurs at several sites on parent DNA
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• DNA polymerase elongates chainadds nucleotides
• 5 to 3 direction only
• 3 to 5 strand made as Okazaki fragments

DNA ligase joins ends Okazaki fragments and
pieces from different origins of replication
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22.41 In the replication of a DNA molecule, 2
daughter molecules, Q and R, are formed. The
following sequence is part of the newly formed
strand in daughter molecule Q. 5 A C T T A G
3 Indicate the corresponding sequence in a. The
newly formed strand in daughter molecule R
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• The parent strand in daughter molecule Q
• The parent strand in daughter molecule R

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• Protein Synthesis making protein
• uses information carried in DNA
• General process
• DNA RNA protein
• 4 steps
• Transcription
• Editing
• Transfer to cytoplasm
• Translation

transcription
translation
in nucleus
in cytoplasm
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• Transcription making an RNA copy of the DNA,
  called heterogeneous nuclear RNA (hnRNA)
• also called primary transcript RNA (ptRNA)
• Made like replication, but only 1 strand copied

hnRNA complementary to DNA but A paired with U
instead of T
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• genes information on DNA for making proteins
• 2 parts exons sequences for making protein
• introns extra sequences, probably
  for regulation
• Editing removing the introns from hnRNA to make
  messenger RNA (mRNA) just exons
• Done by enzymes with the help of small nuclear
  RNA (snRNA) (100-200 nucleotides)

exon
intron
exon
intron
exon
hnRNA
Editing by enzymes snRNAs
mRNA
exon
exon
exon
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• Transfer to cytoplasm. mRNA carries the message
  from the nucleus to the cytoplasmto ribosomes
• Ribosomes made of protein and ribosomal RNA
  (rRNA)
• Ribosomes are free in cytoplasm and on
  endoplasmic reticulum
• 4. Translation reading of mRNA by ribosomes

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Begins at initiation codon (AUG) also codes for
met Transfer RNA (tRNA) brings in appropriate
amino acid, where it starts or adds to a protein
chain Genetic Code language of RNA. Made of
codons. Codon a set of 3 nucleotides that
specifies a particular amino acid
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Genetic Code
Only 1 amino acid per codon reads 5 to
3 degenerate more than 1 codon for some amino
acids, usually varies in 3rd position universal
most living things use the same genetic code 1
start codon AUG (met) 3 stop codons UAA, UAG,
UGA
22.79 Predict the amino acid sequence coded by
the mRNA 5- A U G A A A G A A G A C C U A -3
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Ribosomes move along mRNA, tRNA brings in amino
acids, enzymes (peptidyl transferases) move amino
acid from tRNA to growing protein chain
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Structure of tRNA cloverleaf with 3 hairpin
loops and a stem where amino acid
attaches Anticodon set of 3 nucleotides
complementary to codon for the amino acid on the
tRNA stem
UUC complementary to codon AAG, which gives
lysine upon translation
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Alternative views of tRNA structure
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Determine the amino acid sequence specified by
the following DNA sequence, showing all
intermediate steps. 3- GCGCATTTGCACCTTGGCACG -5
exon
exon
intron