Biology 1115 Chapter 16
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Who introduced the double-helical model for the structure of DNA?
James Watson and Francis Crick
What is encoded in DNA and reproduced in all cells if the body?
Where are genes located?
What are the two components of chromosomes?
who began the discovery of the genetic role of DNA? How did he experiment this?
- Fredrick Griffith
- he worked with two strains of bacterium, one pathogenic and one harmless.
What is transformation?
a change in genotype and phenotype due to assimilation of foreign DNA.
Why might some biologists have thought that proteins would be a better candidate than DNA to carry genetic material?
number of amino acids in protein is more than number of nucleotides in DNA
What elements are found in nucleic acid?
carbon, hydrogen, oxygen, nitrogen, phosphate
What elements are found in proteins?
carbon, hydrogen, oxygen, nitrogen, and sulphur
What did Alfred Hershey and Martha Chase concluded after their experiment with phages?
they concluded that the injected DNA of the phage provides the genetic information
What do nucleotides consist of?
- nitrogenous base
- phosphate group
What does Chargaff's rules state?
that in any species there is an equal number of A and T bases and an equal number of G and C bases
What did Rosalind Franklin discover?
They discovered the that phosphate group and sugar were in the backbones of DNA with the nitrogenous base pairs in the interior.
How is the nitrogenous bases paired generally?
a purine is paired with pyrimidine and this resulted in a uniform width
What do you know about the structure of DNA that suggests a mechanism for replication?
each strand can act as a template
Why is possible for each strand of DNA to act as a template for building a new stand in replication?
because the two strands of DNA are complementary
What was the semi-conservative model?
predicts that when a double helix replicates, each daughter molecule will have one old strand and one newly made strand
What was the conservative model?
the two parent strands rejoin
What was the dispersive model?
each strand is a mix of old and new
Where does DNA replication begin?
at sites called Origins of replication
What happens in DNA replication?
The two DNA strands are separated, opening up a replication bubble.
In which direction does replication proceed?
in both directions from each origin, until the entire molecule is copied
Which direction does DNA replication synthesize? Nucleotide's can only be added to which end?
what is at the end of each replication bubble?
What is a replication fork?
a y-shaped region where the new DNA strands are elongating.(extending)
What are helicases?
enzymes that untwist the double helix at the replication forks.
What is a single-strand binding protein?
binds to and stabilizes single-stranded DNA until it can until it can be used as a template.
What is topoisomerase? (2)
- corrects "over winding" ahead of replication forks, by breaking, swiveling, and rejoining DNA strands
- reduces tension
What is DNA polymerase?
enzyme that catalyzes the elongation of new DNA at a replication fork
Most DNA polymerases require what two things?
- DNA template strand
What are the two main DNA polymerases in E. coli?
- DNA polymerase 3
- DNA polymerase 1
What can DNA polymerase do and not do?
- DNA polymerase cannot initiate synthesis of a polynucleotide
- they can only add nucleotides to the 3' end
what is the initial nucleotide strand in DNA replication?
What is the function of primase?
an enzyme that can start an RNA chain from scratch and adds RNA nucleotides one at a time using the parental DNA as a template
What end serves as the starting point for the new DNA strand?
Each nucleotide that is added to a growing DNA strand is a _____________. What is an example?
- nucleoside triphosphate
As each monomer of dATP joins the DNA strand, what happens?
it loses two phosphate groups as a molecule of pyrophosphate
A DNA strand can only elongate in which direction?
5' to 3' direction
What is the function of DNA polymerase 3?
synthesizes new DNA strand by covalently adding nucleotides to the 3' end of pre-existing DNA or RNA primer
which way does polymerase 3 synthesize when synthesizing a leading strand?
moving towards the replication fork
which way does polymerase 3 synthesize when synthesizing a lagging strand?
away from the replication fork
How is the lagging strand synthesized?
synthesized as a series of segments called Okazaki fragments, which are joined together by DNA ligase
What is the function of polymerase 1?
removes RNA nucleotides of primer from 5' end and replaces them with DNA nucleotides
What are the two functions of DNA ligase?
- joins 3' end of DNA that replaces primer to rest of leading strand
- joins Okazaki fragments of lagging strands
__________ proofread newly made DNA, replacing any incorrect nucleotides
What happens in mismatch repair of DNA?
repair enzymes correct errors in base pairing
What are some things DNA can be damaged by? (5)
- radioactive emissions
- UV light
- certain molecules
What is the function of nuclease in nucleotide excision repair?
cuts out and replaces damaged stretches of DNA
What are telomeres and what are their function?
- TTAGGG repeated 100 to 1000 times
- they postpone the erosion of genes near the ends of DNA molecules
What is telomerase?
an enzyme that catalyzes the lengthening of telomeres in germ cells
How can telomerase protect cells from cancerous growth?
by limiting the number of cell divisions
Define chromatin. (2)
- only found in eukaryotic cells
- is a complex of DNA and protein and is found in nucleus
Eukaryotic chromosomal DNA molecules have at their ends nucleotide sequence called __________.
What is euchromatin?
loosely packed chromatin
What is heterochromatin?
highly condensed chromatin
What difficulty does the dense packing of heterochromatin cause?
make it difficult for the cell to express genetic information coded in these regions
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