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№2 слайд
![Overview Life s Operating](/documents_6/1d23d5411503d497ffaccd18503b1deb/img1.jpg)
Содержание слайда: Overview: Life’s Operating Instructions
In 1953, James Watson and Francis Crick introduced an elegant double-helical model for the structure of deoxyribonucleic acid, or DNA
DNA, the substance of inheritance, is the most celebrated molecule of our time
Hereditary information is encoded in DNA and reproduced in all cells of the body
This DNA program directs the development of biochemical, anatomical, physiological, and (to some extent) behavioral traits
№5 слайд
![The Search for the Genetic](/documents_6/1d23d5411503d497ffaccd18503b1deb/img4.jpg)
Содержание слайда: The Search for the Genetic Material: Scientific Inquiry
When T. H. Morgan’s group showed that genes are located on chromosomes, the two components of chromosomes—DNA and protein—became candidates for the genetic material
The key factor in determining the genetic material was choosing appropriate experimental organisms
The role of DNA in heredity was first discovered by studying bacteria and the viruses that infect them
№9 слайд
![In , Oswald Avery, Maclyn](/documents_6/1d23d5411503d497ffaccd18503b1deb/img8.jpg)
Содержание слайда: In 1944, Oswald Avery, Maclyn McCarty, and Colin MacLeod announced that the transforming substance was DNA
In 1944, Oswald Avery, Maclyn McCarty, and Colin MacLeod announced that the transforming substance was DNA
Their conclusion was based on experimental evidence that only DNA worked in transforming harmless bacteria into pathogenic bacteria
Many biologists remained skeptical, mainly because little was known about DNA
№13 слайд
![In , Alfred Hershey and](/documents_6/1d23d5411503d497ffaccd18503b1deb/img12.jpg)
Содержание слайда: In 1952, Alfred Hershey and Martha Chase performed experiments showing that DNA is the genetic material of a phage known as T2
In 1952, Alfred Hershey and Martha Chase performed experiments showing that DNA is the genetic material of a phage known as T2
To determine this, they designed an experiment showing that only one of the two components of T2 (DNA or protein) enters an E. coli cell during infection
They concluded that the injected DNA of the phage provides the genetic information
№20 слайд
![Two findings became known as](/documents_6/1d23d5411503d497ffaccd18503b1deb/img19.jpg)
Содержание слайда: Two findings became known as Chargaff’s rules
Two findings became known as Chargaff’s rules
The base composition of DNA varies between species
In any species the number of A and T bases are equal and the number of G and C bases are equal
The basis for these rules was not understood until the discovery of the double helix
№22 слайд
![Building a Structural Model](/documents_6/1d23d5411503d497ffaccd18503b1deb/img21.jpg)
Содержание слайда: Building a Structural Model of DNA: Scientific Inquiry
After DNA was accepted as the genetic material, the challenge was to determine how its structure accounts for its role in heredity
Maurice Wilkins and Rosalind Franklin were using a technique called X-ray crystallography to study molecular structure
Franklin produced a picture of the DNA molecule using this technique
№26 слайд
![Franklin s X-ray](/documents_6/1d23d5411503d497ffaccd18503b1deb/img25.jpg)
Содержание слайда: Franklin’s X-ray crystallographic images of DNA enabled Watson to deduce that DNA was helical
Franklin’s X-ray crystallographic images of DNA enabled Watson to deduce that DNA was helical
The X-ray images also enabled Watson to deduce the width of the helix and the spacing of the nitrogenous bases
The pattern in the photo suggested that the DNA molecule was made up of two strands, forming a double helix
№31 слайд
![Watson and Crick built models](/documents_6/1d23d5411503d497ffaccd18503b1deb/img30.jpg)
Содержание слайда: Watson and Crick built models of a double helix to conform to the X-rays and chemistry of DNA
Watson and Crick built models of a double helix to conform to the X-rays and chemistry of DNA
Franklin had concluded that there were two outer sugar-phosphate backbones, with the nitrogenous bases paired in the molecule’s interior
Watson built a model in which the backbones were antiparallel (their subunits run in opposite directions)
№32 слайд
![At first, Watson and Crick](/documents_6/1d23d5411503d497ffaccd18503b1deb/img31.jpg)
Содержание слайда: At first, Watson and Crick thought the bases paired like with like (A with A, and so on), but such pairings did not result in a uniform width
At first, Watson and Crick thought the bases paired like with like (A with A, and so on), but such pairings did not result in a uniform width
Instead, pairing a purine with a pyrimidine resulted in a uniform width consistent with the X-ray data
№34 слайд
![Watson and Crick reasoned](/documents_6/1d23d5411503d497ffaccd18503b1deb/img33.jpg)
Содержание слайда: Watson and Crick reasoned that the pairing was more specific, dictated by the base structures
Watson and Crick reasoned that the pairing was more specific, dictated by the base structures
They determined that adenine (A) paired only with thymine (T), and guanine (G) paired only with cytosine (C)
The Watson-Crick model explains Chargaff’s rules: in any organism the amount of A = T, and the amount of G = C
№37 слайд
![The Basic Principle Base](/documents_6/1d23d5411503d497ffaccd18503b1deb/img36.jpg)
Содержание слайда: The Basic Principle: Base Pairing to a Template Strand
Since the two strands of DNA are complementary, each strand acts as a template for building a new strand in replication
In DNA replication, the parent molecule unwinds, and two new daughter strands are built based on base-pairing rules
№42 слайд
![Watson and Crick s](/documents_6/1d23d5411503d497ffaccd18503b1deb/img41.jpg)
Содержание слайда: Watson and Crick’s semiconservative model of replication predicts that when a double helix replicates, each daughter molecule will have one old strand (derived or “conserved” from the parent molecule) and one newly made strand
Watson and Crick’s semiconservative model of replication predicts that when a double helix replicates, each daughter molecule will have one old strand (derived or “conserved” from the parent molecule) and one newly made strand
Competing models were the conservative model (the two parent strands rejoin) and the dispersive model (each strand is a mix of old and new)
№44 слайд
![Experiments by Matthew](/documents_6/1d23d5411503d497ffaccd18503b1deb/img43.jpg)
Содержание слайда: Experiments by Matthew Meselson and Franklin Stahl supported the semiconservative model
Experiments by Matthew Meselson and Franklin Stahl supported the semiconservative model
They labeled the nucleotides of the old strands with a heavy isotope of nitrogen, while any new nucleotides were labeled with a lighter isotope
№45 слайд
![The first replication](/documents_6/1d23d5411503d497ffaccd18503b1deb/img44.jpg)
Содержание слайда: The first replication produced a band of hybrid DNA, eliminating the conservative model
The first replication produced a band of hybrid DNA, eliminating the conservative model
A second replication produced both light and hybrid DNA, eliminating the dispersive model and supporting the semiconservative model
№50 слайд
![Getting Started Replication](/documents_6/1d23d5411503d497ffaccd18503b1deb/img49.jpg)
Содержание слайда: Getting Started
Replication begins at particular sites called origins of replication, where the two DNA strands are separated, opening up a replication “bubble”
A eukaryotic chromosome may have hundreds or even thousands of origins of replication
Replication proceeds in both directions from each origin, until the entire molecule is copied
№57 слайд
![At the end of each](/documents_6/1d23d5411503d497ffaccd18503b1deb/img56.jpg)
Содержание слайда: At the end of each replication bubble is a replication fork, a Y-shaped region where new DNA strands are elongating
At the end of each replication bubble is a replication fork, a Y-shaped region where new DNA strands are elongating
Helicases are enzymes that untwist the double helix at the replication forks
Single-strand binding proteins bind to and stabilize single-stranded DNA
Topoisomerase corrects “overwinding” ahead of replication forks by breaking, swiveling, and rejoining DNA strands
№60 слайд
![An enzyme called primase can](/documents_6/1d23d5411503d497ffaccd18503b1deb/img59.jpg)
Содержание слайда: An enzyme called primase can start an RNA chain from scratch and adds RNA nucleotides one at a time using the parental DNA as a template
An enzyme called primase can start an RNA chain from scratch and adds RNA nucleotides one at a time using the parental DNA as a template
The primer is short (5–10 nucleotides long), and the 3 end serves as the starting point for the new DNA strand
№61 слайд
![Synthesizing a New DNA Strand](/documents_6/1d23d5411503d497ffaccd18503b1deb/img60.jpg)
Содержание слайда: Synthesizing a New DNA Strand
Enzymes called DNA polymerases catalyze the elongation of new DNA at a replication fork
Most DNA polymerases require a primer and a DNA template strand
The rate of elongation is about 500 nucleotides per second in bacteria and 50 per second in human cells
№62 слайд
![Each nucleotide that is added](/documents_6/1d23d5411503d497ffaccd18503b1deb/img61.jpg)
Содержание слайда: Each nucleotide that is added to a growing DNA strand is a nucleoside triphosphate
Each nucleotide that is added to a growing DNA strand is a nucleoside triphosphate
dATP supplies adenine to DNA and is similar to the ATP of energy metabolism
The difference is in their sugars: dATP has deoxyribose while ATP has ribose
As each monomer of dATP joins the DNA strand, it loses two phosphate groups as a molecule of pyrophosphate
№70 слайд
![To elongate the other new](/documents_6/1d23d5411503d497ffaccd18503b1deb/img69.jpg)
Содержание слайда: To elongate the other new strand, called the lagging strand, DNA polymerase must work in the direction away from the replication fork
To elongate the other new strand, called the lagging strand, DNA polymerase must work in the direction away from the replication fork
The lagging strand is synthesized as a series of segments called Okazaki fragments, which are joined together by DNA ligase
№86 слайд
![Proofreading and Repairing](/documents_6/1d23d5411503d497ffaccd18503b1deb/img85.jpg)
Содержание слайда: Proofreading and Repairing DNA
DNA polymerases proofread newly made DNA, replacing any incorrect nucleotides
In mismatch repair of DNA, repair enzymes correct errors in base pairing
DNA can be damaged by exposure to harmful chemical or physical agents such as cigarette smoke and X-rays; it can also undergo spontaneous changes
In nucleotide excision repair, a nuclease cuts out and replaces damaged stretches of DNA
№88 слайд
![Evolutionary Significance of](/documents_6/1d23d5411503d497ffaccd18503b1deb/img87.jpg)
Содержание слайда: Evolutionary Significance of Altered DNA Nucleotides
Error rate after proofreading repair is low but not zero
Sequence changes may become permanent and can be passed on to the next generation
These changes (mutations) are the source of the genetic variation upon which natural selection operates
№89 слайд
![Replicating the Ends of DNA](/documents_6/1d23d5411503d497ffaccd18503b1deb/img88.jpg)
Содержание слайда: Replicating the Ends of DNA Molecules
Limitations of DNA polymerase create problems for the linear DNA of eukaryotic chromosomes
The usual replication machinery provides no way to complete the 5 ends, so repeated rounds of replication produce shorter DNA molecules with uneven ends
This is not a problem for prokaryotes, most of which have circular chromosomes
№93 слайд
![Eukaryotic chromosomal DNA](/documents_6/1d23d5411503d497ffaccd18503b1deb/img92.jpg)
Содержание слайда: Eukaryotic chromosomal DNA molecules have special nucleotide sequences at their ends called telomeres
Eukaryotic chromosomal DNA molecules have special nucleotide sequences at their ends called telomeres
Telomeres do not prevent the shortening of DNA molecules, but they do postpone the erosion of genes near the ends of DNA molecules
It has been proposed that the shortening of telomeres is connected to aging
№95 слайд
![If chromosomes of germ cells](/documents_6/1d23d5411503d497ffaccd18503b1deb/img94.jpg)
Содержание слайда: If chromosomes of germ cells became shorter in every cell cycle, essential genes would eventually be missing from the gametes they produce
If chromosomes of germ cells became shorter in every cell cycle, essential genes would eventually be missing from the gametes they produce
An enzyme called telomerase catalyzes the lengthening of telomeres in germ cells
№96 слайд
![The shortening of telomeres](/documents_6/1d23d5411503d497ffaccd18503b1deb/img95.jpg)
Содержание слайда: The shortening of telomeres might protect cells from cancerous growth by limiting the number of cell divisions
The shortening of telomeres might protect cells from cancerous growth by limiting the number of cell divisions
There is evidence of telomerase activity in cancer cells, which may allow cancer cells to persist
№97 слайд
![Concept . A chromosome](/documents_6/1d23d5411503d497ffaccd18503b1deb/img96.jpg)
Содержание слайда: Concept 16.3 A chromosome consists of a DNA molecule packed together with proteins
The bacterial chromosome is a double-stranded, circular DNA molecule associated with a small amount of protein
Eukaryotic chromosomes have linear DNA molecules associated with a large amount of protein
In a bacterium, the DNA is “supercoiled” and found in a region of the cell called the nucleoid
№107 слайд
![Chromatin undergoes changes](/documents_6/1d23d5411503d497ffaccd18503b1deb/img106.jpg)
Содержание слайда: Chromatin undergoes changes in packing during the cell cycle
Chromatin undergoes changes in packing during the cell cycle
At interphase, some chromatin is organized into a 10-nm fiber, but much is compacted into a 30-nm fiber, through folding and looping
Though interphase chromosomes are not highly condensed, they still occupy specific restricted regions in the nucleus
№112 слайд
![Most chromatin is loosely](/documents_6/1d23d5411503d497ffaccd18503b1deb/img111.jpg)
Содержание слайда: Most chromatin is loosely packed in the nucleus during interphase and condenses prior to mitosis
Most chromatin is loosely packed in the nucleus during interphase and condenses prior to mitosis
Loosely packed chromatin is called euchromatin
During interphase a few regions of chromatin (centromeres and telomeres) are highly condensed into heterochromatin
Dense packing of the heterochromatin makes it difficult for the cell to express genetic information coded in these regions
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