Unit 3 Lecture 4 10/24/22 Flashcards
In 1953, James Watson and Francis Crick introduced an elegant double-helical model for the structure of __________, or __________
deoxyribonucleic acid or DNA
__________information is encoded in DNA and reproduced in all cells of the body (DNA replication)
heredity
The two components of chromosomes—__________ and __________—became candidates for the genetic material
1.DNA
2.Protein
Viruses that infect bacteria are called __________
bacteriophages
Griffith worked with two strains of a bacterium, one __________ and one __________
1.pathogenic
2.harmless
He called this phenomenon __________, now defined as a change in genotype and phenotype due to assimilation of foreign DNA
transformation
Later work by Oswald Avery and others identified the transforming substance as __________
DNA
Many biologists remained skeptical, mainly because little was known about DNA and they thought __________were better candidates for the genetic material
Proteins
To determine this, they designed an experiment showing that only the __________of the T2 phage, and not the __________, enters an E. coli cell during infection
1.DNA
2.protein
It was known that DNA is a polymer of __________, each consisting of a nitrogenous base, a sugar, and a phosphate group
Nucleotides
Two findings became known as __________
Chargaff’s rules
The base composition of DNA ____________________
varies between species
In any species the number of __________bases is equal, and the number of __________bases is equal
A and T
G and C
The basis for these rules was not understood until the discovery of the __________
double helix
Maurice Wilkins and Rosalind Franklin were using a technique called ____________________to study molecular structure
X-ray Crystallography
The pattern in the photo suggested that the DNA molecule was made up of two strands, forming a __________
double helix
Franklin had concluded that there were two outer __________________________, with the ____________________ paired in the molecule’s interior
1.sugar-phosphate backbones
2.nitrogenous bases
Watson built a model in which the backbones were __________ (their subunits run in opposite directions)
antiparallel
Instead, pairing a __________with a __________ resulted in a uniform width consistent with the X-ray data
1.purine
2.pyrimidine
They determined that __________paired only with __________, and __________ paired only with __________
1&2.adenine with thymine
3&4.guanine with cytosine
The __________ explains __________: in any organism the amount __________, and the amount of __________
Watson-Crick model
Chargaff’s rules
A=T
G=C
The relationship between structure and function is manifest in the __________
Double helix
Watson and Crick noted that the specific base pairing suggested a possible __________for genetic material
Copying mechanism
Watson and Crick’s __________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
Semiconservative model
Competing models were the __________ (the two parent strands rejoin) and the __________ (each strand is a mix of old and new)
conservative model
dispersive model
Experiments by Matthew Meselson and Franklin Stahl supported the __________
Semiconservative model
Replication begins at particular sites called ____________________, where the two DNA strands are separated, opening a ____________________
origins of replication
replication bubble
At each end of a bubble is a ____________________, a Y-shaped region where the parental strands of DNA are being unwound
replication fork
__________are enzymes that untwist the double helix at the replication forks
Helicases
____________________bind to and stabilize single-stranded DNA
single-strand binding proteins
__________ relieves the strain caused by tight twisting ahead of the replication fork by breaking, swiveling, and rejoining DNA strands
Topoisomerase
__________replication bubbles form and eventually fuse, speeding up the copying of DNA
Multiple
__________cannot initiate synthesis of a polynucleotide; they can only add nucleotides to an already existing chain base-paired with the template
DNA polymerases
The initial nucleotide strand is a short __________
RNA primer
The enzyme __________starts an RNA chain from a single RNA nucleotide and adds RNA nucleotides one at a time using the parental DNA as a template
Primase
Enzymes called __________catalyze the elongation of new DNA at a replication fork
DNA polmerases
The rate of elongation is about __________ per second in bacteria and __________in human cells
500 nucleotides
50 per second
__________is used to make DNA and is similar to the ATP of energy metabolism
dATP
The difference is in the sugars: dATP has __________, while ATP has __________
Deoxyribose
Ribose
As each monomer nucleotide joins the DNA strand, it loses two phosphate groups as a molecule of __________
Pyrophosphate
The __________structure of the double helix affects replication
antiparallel
Along one template strand of DNA, the __________synthesizes a __________continuously, moving toward the replication fork
DNA polymerase
Leading strand
To elongate the other new strand, called the __________, DNA polymerase must work in the direction __________from the replication fork
lagging strand
away
The lagging strand is synthesized as a series of segments called __________
Okazaki fragments
After formation of Okazaki fragments, __________ removes the __________and replaces the nucleotides with DNA
DNA polymerase 1
RNA primer
The remaining gaps are joined together by DNA __________
ligase
__________proofread newly made DNA, replacing any incorrect nucleotides
DNA polymerases
In nucleotide__________, a __________cuts out and replaces damaged stretches of DNA
excision repair
nuclease
Error rate after proofreading repair is low but __________zero
not
These changes __________are the source of the genetic variation upon which __________operates
mutations
natural selection
Limitations of DNA polymerase create problems for the __________of eukaryotic chromosomes
linear DNA
Eukaryotic chromosomal DNA molecules have special nucleotide sequences at their ends called __________
telomeres
__________ do not prevent the shortening of DNA molecules, but they do postpone it
Telomeres
It has been proposed that the shortening of telomeres is connected to __________
aging
An enzyme called __________ catalyzes the lengthening of telomeres in germ cells Telomerase is not active in most human somatic cells
telomerase
The bacterial chromosome is a double-stranded, __________ DNA molecule associated with a __________ amount of protein
circular
small
Eukaryotic chromosomes have __________ DNA molecules associated with a __________ amount of protein
linear
large
In a bacterium, the DNA is “supercoiled” and found in a region of the cell called the __________
nucleoid
__________, a complex of DNA and protein, is found in the nucleus of eukaryotic cells
Chromatin
__________ fit into the nucleus through an elaborate, multilevel system of packing
Chromosomes
__________ undergoes striking changes in the degree of packing during the course of the cell cycle
Chromatin
At __________, most of the chromatin is compacted into a 30-nm fiber, which is folded further in some areas by looping
interphase
This condensed chromatin is called __________; the more dispersed, less compacted chromatin is called __________
heterochromatin
euchromatin
Dense packing of the heterochromatin makes it largely __________ to the machinery responsible for transcribing genetic information
inaccessible
Complementary base pairing of DNA is the basis for __________, the base pairing of one strand of a nucleic acid to another, complementary sequence
nucleic acid hybridization
__________ forms the foundation of virtually every technique used in __________, the direct manipulation of genes for practical purposes
nucleic acid hybridization
genetic engineering
