15. Figure 11-10
Page 228
DNA polymerase
DNA polymerase Origin of replication
Single-stranded
binding proteins
Direction of
replicationRNA primer
DNA
helicase
Twist introduced into
the helix by unwinding
3’
5’
3’
5’
3’
5’
3’
5’
3’
5’
3’
5’
3’
5’
3’
5’
3’
3’
16.
17. 3’
Leading strand
RNA primer
DNA polymerase
Replication fork
Lagging strand
(first Okazaki fragment)
Direction of
replication
DNA helix
5’
3’
5’
3’
5’
3’
5’
18. Leading strand
DNA ligase Third Okazaki fragment
Direction of
replication
3’
5’
3’
5’
3’
5’
3’5’
3’
5’
Lagging strand
19. Leading strand
DNA ligase Third Okazaki fragment
Direction of
replication
3’
5’
3’
5’
3’
5’
3’5’
3’
5’
Lagging strand
43. (continue to next slide)
–AAA...
Poly-A tail
3’ end
5' end
1st
exon
2nd
exon
3rd
exon
Protein-coding region
44. Nuclear pore
Transport through nuclear
envelope to cytosol
Nuclear envelope
Cytosol
5' end
Leader Start codon Stop codon
–AAA...
Poly-A tail
3' end
Figure: 09.3
Title:
The Watson-Crick model of DNA structure
Caption:
(a) Two strands of DNA wind about each other in a double helix, like a twisted ladder. The two DNA strands run in opposite directions. This directionality is especially clear at the ends of the double helix, where the terminal nucleotide of one strand has an unbonded (“free”) sugar and the terminal nucleotide on the other strand has an unbonded (“free”) phosphate. (b) Complementary base pairs (adenine and thymine, guanine and cytosine) hold the two DNA strands together. (c) Hydrogen bonding between specific base pairs in the center of the helix hold the two strands together. Three hydrogen bonds hold guanine to cytosine; two hydrogen bonds hold adenine to thymine.
Figure: 10.3
Title:
Genetic information flows from DNA to RNA to protein
Caption:
Cellular information is stored within the base sequence of DNA. Transcription, the process of RNA synthesis, occurs in the nucleus. During transcription, the nucleotide sequence in a gene specifies the nucleotide sequence in a complementary RNA molecule. For protein-encoding genes, the product is an mRNA molecule that exits from the nucleus and enters the cytoplasm where translation occurs. During translation, the sequence in an mRNA molecule specifies the amino acid sequence in a protein.
Figure: 09.4
Title:
Basic features of DNA replication
Caption:
During replication, enzymes separate the parental DNA double helix, breaking the hydrogen bonds between complementary bases. Other enzymes select complementary nucleotides and add them to the growing daughter strands. Each parental strand and its new daughter strand form a new double helix.
Figure: 09.5
Title:
Replication bubble
Caption:
DNA replication begins when DNA helicase and related enzymes unwind portions of the parental DNA double helix, creating a replication bubble. In complex cells, DNA replication occurs simultaneously at many locations on the parental DNA double helix, resulting in multiple replication bubbles. DNA replication is completed when all adjacent replication bubbles meet to form two complete and separate DNA double helices.
Figure: 09.6
Title:
Details of DNA replication
Caption:
(a) One DNA strand can be synthesized as a long, continuous strand. The other DNA strand must be synthesized as a series of short segments that are connected by DNA ligase. (b) Synthesis of new DNA strands involves complex enzyme machinery. 1) A large complex of enzymes assembles at each replication fork. Within this complex, DNA helicase separates the two DNA strands, unwinding a small portion of the parental double helix. The complex also contains two DNA polymerase molecules, one attached to each parental strand. 2) The two DNA polymerase molecules match up complementary free nucleotides with the parental DNA strands and join up their sugar-phosphates to form the backbones of the new DNA strands. Because nucleotides in DNA can only be added to the free sugar end of a strand, the DNA polymerase on one strand (upper strand in this diagram) can synthesize a complementary DNA strand in a continuous segment. The other DNA polymerase (on the lower, looping strand in this diagram) must synthesize its complementary DNA strand in small segments as the DNA replication machinery unwinds more and more of the original DNA double helix. 3) The replication machinery advances, unwinding more parental DNA and synthesizing more complementary daughter DNA. 4) Another enzyme, DNA ligase, joins together the segments of newly synthesized DNA, finally producing a continuous daughter strand that is complementary to the original strand. Replication produces two DNA double helices, each of which has one strand from the original DNA double helix and one strand that has just been synthesized.
Figure: 09.6a
Title:
Details of DNA replication
Caption:
(a) One DNA strand can be synthesized as a long, continuous strand. The other DNA strand must be synthesized as a series of short segments that are connected by DNA ligase.
Figure: 09.UN06b1
Title:
Details of DNA replication
Caption:
(b) Synthesis of new DNA strands involves complex enzyme machinery. 1) A large complex of enzymes assembles at each replication fork. Within this complex, DNA helicase separates the two DNA strands, unwinding a small portion of the parental double helix. The complex also contains two DNA polymerase molecules, one attached to each parental strand. 2) The two DNA polymerase molecules match up complementary free nucleotides with the parental DNA strands and join up their sugar-phosphates to form the backbones of the new DNA strands. Because nucleotides in DNA can only be added to the free sugar end of a strand, the DNA polymerase on one strand (upper strand in this diagram) can synthesize a complementary DNA strand in a continuous segment. The other DNA polymerase (on the lower, looping strand in this diagram) must synthesize its complementary DNA strand in small segments as the DNA replication machinery unwinds more and more of the original DNA double helix.
Figure: 09.UN06b2
Title:
Details of DNA replication
Caption:
(b) 3) The replication machinery advances, unwinding more parental DNA and synthesizing more complementary daughter DNA. 4) Another enzyme, DNA ligase, joins together the segments of newly synthesized DNA, finally producing a continuous daughter strand that is complementary to the original strand. Replication produces two DNA double helices, each of which has one strand from the original DNA double helix and one strand that has just been synthesized.
Figure: 09.UN04
Title:
DNA replication
Caption:
DNA replication
Figure: 10.4
Title:
Transcription occurs in three steps
Caption:
Most chromosomes contain hundreds or thousands of genes. Each gene occupies a particular position in the DNA of the chromosome. Within the gene, one of the DNA strands will serve as the template for RNA synthesis. (a) Initiation: The enzyme RNA polymerase binds to the promoter region of DNA near the beginning of a gene. In different cells, RNA polymerase binds to the promoters of different genes, depending on conditions inside and outside the cell. Binding of RNA polymerase forces the DNA double helix near the promoter to separate. (b) Elongation: RNA polymerase then travels along the DNA template strand, catalyzing the addition of nucleotides into an mRNA molecule. The nucleotides in the mRNA are complementary to the template strand of the DNA. The DNA double helix rewinds a short distance after RNA polymerase passes. The process continues until (c) termination: At the end of a gene, the RNA polymerase encounters a sequence of DNA called a termination signal. (d) At this point, RNA polymerase detaches from the DNA and releases the RNA molecule, allowing the DNA double helix to completely rewind. Initiation of another round of transcription can occur before the previous RNA polymerase has completed its RNA, so that many RNA molecules can be produced nearly simultaneously from a single gene.
Figure: 10.4ab
Title:
Intiation and elongation of RNA transcription
Caption:
Intiation and elongation of RNA transcription
Figure: 10.4cd
Title:
Termination of RNA transcription
Caption:
Termination of RNA transcription
Figure: 10.5
Title:
RNA transcription in action
Caption:
This electron micrograph shows the progress of RNA transcription in the egg of an African clawed toad. In each treelike structure, the central “trunk” is DNA and the “branches” are RNA molecules. A series of RNA polymerase molecules are traveling down the DNA, synthesizing RNA as they go. The beginning of the gene is on the left. Therefore, the short RNA molecules on the left have just begun to be synthesized; the long RNA molecules on the right are almost finished.
Figure: 10.E1
Title:
How insertion mutations helped crack the genetic code
Caption:
How insertion mutations helped crack the genetic code.
Figure: 10.7
Title:
Complementary base pairing is critical at each step in decoding genetic information
Caption:
(a) DNA contains two strands: the template strand is used by RNA polymerase to synthesize an RNA molecule; the other strand, which is complementary to the template strand, is needed for DNA replication. (b) Bases in the template strand of DNA are transcribed into a complementary mRNA. Codons are sequences of three bases that specify an amino or a stop during protein synthesis. (c) Unless it is a stop codon, each mRNA codon forms base pairs with the anticodon of a tRNA molecule that carries a specific amino acid. (d) The ribosome links the amino acids together, forming the protein.
Figure: 10.8
Title:
An overview of “information flow” in a cell
Caption:
This simplified diagram shows the major steps from DNA to protein to chemical reactions catalyzed by enzymes. Regulation of gene expression may occur at any or all steps.
Figure: 10.2
Title:
Cells synthesize three major types of RNA
Caption:
RNA consists of a single nucleotide strand whose bases are complementary to the bases within the template strand of the gene. There are three major types of RNA: (a) Messenger RNA (mRNA) carries within its base sequence the information for the amino acid sequence of a protein. (b) Ribosomes contain both ribosomal RNA (rRNA) and proteins. The ribosome is divided into a small and large subunit that join together during protein synthesis. The small subunit binds the mRNA; the large subunit binds tRNA and catalyzes the formation of bonds between amino acids to form a protein. (c) One side of transfer RNA contains an anticodon, which is a sequence of three nucleotides that can form base pairs with a codon in mRNA. Enzymes within the cytoplasm attach a specific amino acid to the opposite side of the tRNA so that it can carry the proper amino acid to the ribosome for incorporation into a new protein.
