Cell Division and Mitosis

1
DMA

• Why is it vital for a cell to perform DNA
  replication?

http//www.gis.harvard.edu/images/dna.gif
2
From DNA to Proteins

• Starr/Taggarts
• Biology
• The Unity and Diversity of Life, 9e
• Chapter 14

3
Transcription
http//www.nobel.se/medicine/educational/dna/a/tra
nscription/pics/transcription.gif
4
Transcription

• Making mRNA from a DNA template called a
  transcription unit
• Life cannot exist without enzymes and other
  proteins
• The path leading from genes to proteins involves
  two steps
• Transcription involves assembly of a messenger
  RNA molecule and is the first step

5
Transcription
Translation
6
RNA

• RNA composed of nucleotides
• Ribose
• Phosphate group
• Bases
• Adenine
• Cytosine
• Guanine
• Uracil

• Messenger RNA mRNA
• Ribosomal RNArRNA
• Transfer RNA tRNA

7
Transcription

• Initiation
• Elongation
• Termination

http//www.geneticengineering.org/chemis/Chemis-Nu
cleicAcid/Graphics/Transcription.gif
8
Initiation
9
Elongation
10
How RNA is Assembled

• Base pairing
• A - U
• C - G

11
Elongation Termination
5 to 3 direction
Transcribed terminator AAUAAA in eukaryotes
http//www.ncc.gmu.edu/dna/mRNAanim.htm
http//www-class.unl.edu/biochem/gp2/m_biology/ani
mation/gene/gene_a2.html
12
mRNA processing
Introns noncoding Exons coding
Leaves nucleus
13
mRNA processing

• Protects mRNA from breakdown
• Attach here signal for ribosomes

protection
http//cats.med.uvm.edu/cats_teachingmod/microbiol
ogy/courses/gene_regulation/images/UMASS.WELLSLEY.
CAP.C03B.MOV
14
Finishing Touches on the mRNA Transcripts

• Modification
• Introns
• Snipped out
• Exons
• Are translated

15
Transcription

• AT
• AT
• AT
• TA
• GC
• GC
• CG
• TA
• CG
• GC
• CG
• AT
• GC
• AT
• Cell Nucleus

16
Transcription

• AT
• AT
• A T
• T A
• G C
• G C
• C G A C G G T C G A
• T
• G C
• C A
• G C T
• Cell Nucleus

17
Transcription

• AT
• AT
• A T
• T A
• G C
• G C
• C G A C G G T C G A
• T C U G C C A G C U
• G C
• C A
• G C T
• Cell Nucleus

18
Transcription

• AT
• AT
• AT
• TA
• GC
• GC
• CG
• TA
• CG
• GC
• CG
• AT
• GC C U G C C A G C U
• AT
• Cell Nucleus

19
DMA

• Why is it vital for a cell to perform
  transcription?

20
Transcription
mRNA processing
mRNA leave via nuclear pores
Translation
21
Translation

• Translation involves assembling amino acids into
  a polypeptide chain, in other words making a
  protein
• Molecules involved
• mRNA
• tRNA
• Amino acids
• rRNA

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mRNA

• Details
• Every sequence of three DNA bases is called a
  triplet
• On mRNA every three bases of mRNA (codon)
  eventually code for an amino acid

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tRNA

• tRNA
• Attachment site for amino acid
• Anticodon

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tRNA
Anticodon sequence of 3 tRNA bases that are
complimentary to mRNA codons
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tRNAs amino acids
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Ribosome

• rRNAs are components of ribosomes as are
  proteins, made by nucleolus

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Ribosomes
A site arrival site for tRNAs P site holding
tRNA that has the growing protein chain E site
exit site for tRNA
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Translation

• In cytoplasm at the ribosome
• 3 stages Initiation Elongation Termination

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Initiation
Small subunit binds 5 cap Start codon binds
with first tRNA anticodon Large subunit binds
last
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Elongation
31
Elongation
Codon recognition
Translocation
Peptide bond formation
32
Termination
3 stop codons UAA, UAG, UGA
protein
http//www.people.virginia.edu/rjh9u/gif/protein.
mov
http//www.ncc.gmu.edu/dna/ANIMPROT.htm
33
Transcription

• AT
• AT
• AT
• TA
• GC
• GC
• CG
• TA
• CG
• GC
• CG
• AT
• GC C U G C C A G C U
• AT
• Cell Nucleus

34
Translation

• tRNA U C G
• rRNA
• mRNA C U G C C A G C U etc.
• rRNA
• Ribosome
• Linked amino acids

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One Gene, One Polypeptide

• Sickle Cell Anemia
• Hemoglobin S and A
• Gene mutation
• Affects protein synthesis
• Amino acid sequences of polypeptide chains are
  encoded in genes

36
How Mutations Affect Protein Synthesis

• Sequences can change
• Substitution
• Insertion
• Deletion
• Gene mutations
• Frameshift mutations
• Transposable elements

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Insertion

• Shift of bases (codon)

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Mutations

• Each gene has a characteristic mutation rate
• Rates vary among species
• Not all are spontaneous

• Mutagens
• UV
• Ionizing radiation
• Gamma rays
• X-Rays
• Chemicals
• Carcinogens