DNA Replication
The unwinding of the helix creates _________ .
(Theta replication) The unwinding of the double helix generates a loop, termed a(n) ______________________. Unwinding occurs at one or both ends of the bubble, making it progressively larger. DNA replication on both of the template strands is simultaneous with unwinding.
What does topoisomerase do?
DNA topoisomerases are ubiquitous enzymes found in all cell types from viruses to man. These enzymes act to regulate DNA supercoiling by catalysing the winding and unwinding of DNA strands.
What are the components of a deoxyribonucleotide?
Deoxyribonucleic acid (DNA) is a long, double-stranded, helical molecule composed of building blocks called deoxyribonucleotides. A deoxyribonucleotide is composed of 3 parts: a molecule of the 5-carbon sugar deoxyribose, a nitrogenous base, and a phosphate group
What is Nitrogen-15 (15N)? What is Nitrogen-14 (14N)? Which one is more common?
14N14.003 074 005 2(9)99.632 (7) 15N15.000 108 898 4(9)0.368 (7)
What is the backbone of DNA made of?
A sugar-phosphate backbone (alternating grey-dark grey) joins together nucleotides in a DNA sequence. The sugar-phosphate backbone forms the structural framework of nucleic acids, including DNA and RNA. This backbone is composed of alternating sugar and phosphate groups, and defines directionality of the molecule.
Telomere don't contain genes? What are they made of?
A telomere is the end of a chromosome. Telomeres are made of repetitive sequences of non-coding DNA that protect the chromosome from damage. Each time a cell divides, the telomeres become shorter.
What is the helix stabilized by?
An α-helix secondary structure is stabilized by hydrogen bonds between carbonyl oxygen and the amino group of every third residue in the helical turn with each helical turn consisting of 3.6 amino acid residues (Fig. 10.1A). The side chain of amino acids is projected outward from the outer helical surface.
Define antiparallel.
Antiparallel: A term applied to two molecules that are side by side but run in opposite directions. The two strands of DNA are antiparallel. The head of one strand is always laid against the tail of the other strand of DNA.
Replication of DNA happens bidirectionally. What does that mean?
Bidirectional replication involves replicating DNA in two directions at the same time resulting in a leading strand (were replication occurs more rapidly) and a lagging strand (with slower replication)
Base pairing is complementary. What does that mean?
Complementary base pairing is the phenomenon where in DNA guanine always hydrogen bonds to cytosine and adenine always binds to thymine. The bond between guanine and cytosine shares three hydrogen bonds compared to the A-T bond which always shares two hydrogen bonds.
Which direction is DNA read?
DNA is read from 3' to 5'. DNA is only synthesized in the 5' to 3' direction.
What is the function of DNA ligase?
DNA ligases play an essential role in maintaining genomic integrity by joining breaks in the phosphodiester backbone of DNA that occur during replication and recombination, and as a consequence of DNA damage and its repair.
What does DNA polymerase III do?
DNA polymerase III holoenzyme is the enzyme primarily responsible for replicative DNA synthesis in E. coli. It carries out primer-initiated 5' to 3' polymerization of DNA on a single-stranded DNA template, as well as 3' to 5' exonucleolytic editing of mispaired nucleotides.
What does DNA polymerase do?
DNA polymerase is responsible for the process of DNA replication, during which a double-stranded DNA molecule is copied into two identical DNA molecules. Scientists have taken advantage of the power of DNA polymerase molecules to copy DNA molecules in test tubes via polymerase chain reaction, also known as PCR.
What are repair enzymes?
DNA repair enzymes. Definition. DNA repair enzymes are enzymes that recognize and correct physical damage in DNA, caused by exposure to radiation, UV light or reactive oxygen species. The correction of DNA damage alleviates loss of genetic information, generation of double-strand breaks, and DNA crosslinkages.
What are the steps of the synthesis of the leading strand of DNA?
DNA replication steps. There are three main steps to DNA replication: initiation, elongation, and termination. In order to fit within a cell's nucleus, DNA is packed into tightly coiled structures called chromatin, which loosens prior to replication, allowing the cell replication machinery to access the DNA strands.
What function do the single-strand DNA-binding proteins serve?
During DNA replication, SSB molecules bind to the newly separated individual DNA strands, keeping the strands separated by holding them in place so that each strand can serve as a template for new DNA synthesis.
Which end of the deoxyribonucleotide is the 5' end? The 3' end?
Each DNA strand has two ends. The 5' end of the DNA is the one with the terminal phosphate group on the 5' carbon of the deoxyribose; the 3' end is the one with a terminal hydroxyl (OH) group on the deoxyribose of the 3' carbon of the deoxyribose.
What is the function of the replisome? How many replisomes are there per replication bubble?
For eukaryotes, numerous replication bubbles form at origins of replication throughout the chromosome. As with prokaryotes, two replisomes are required, one at each replication fork located at the terminus of the replication bubble.
Name four nitrogenous bases.
Four different types of nitrogenous bases are found in DNA: adenine (A), thymine (T), cytosine (C), and guanine (G). In RNA, the thymine is replaced by uracil (U).
Who was Rosalind Franklin?
Franklin is best known for her work on the X-ray diffraction images of DNA, particularly Photo 51, while at King's College London, which led to the discovery of the DNA double helix for which James Watson, Francis Crick and Maurice Wilkins shared the Nobel Prize in Physiology or Medicine in 1962
What function does helicase serve?
Helicases are enzymes that bind and may even remodel nucleic acid or nucleic acid protein complexes. There are DNA and RNA helicases. DNA helicases are essential during DNA replication because they separate double-stranded DNA into single strands allowing each strand to be copied.
How does the origin of replication differ between bacteria and eukaryotes?
In prokaryotic cells, there is only one point of origin, replication occurs in two opposing directions at the same time, and takes place in the cell cytoplasm. Eukaryotic cells on the other hand, have multiple points of origin, and use unidirectional replication within the nucleus of the cell.
What was the experimental design of the Meselson-Stahl experiment.
Meselson and Stahl tested the hypothesis of DNA replication. They cultured bacteria in a 15N medium. 15N is a heavy isotope of nitrogen so the DNA synthesized is of heavy density. They then shifted the bacteria to a 14N medium, DNA was isolated at different times corresponding to replication cycles 0, 1, and 2
How does DNA edit mistakes it makes during synthesis?
Most of the mistakes during DNA replication are promptly corrected by DNA polymerase which proofreads the base that has just been added. In proofreading, the DNA pol reads the newly-added base before adding the next one so a correction can be made.
What is an Okazaki fragment?
Okazaki fragments are short sequences of DNA nucleotides which are synthesized discontinuously and later linked together by the enzyme DNA ligase to create the lagging strand during DNA replication.
What is the function of primase?
Primase is an enzyme that synthesizes short RNA sequences called primers. ... Primase functions by synthesizing short RNA sequences that are complementary to a single-stranded piece of DNA, which serves as its template. It is critical that primers are synthesized by primase before DNA replication can occur.
What is a replication bubble?
Replication Bubble. DNA replication is when one strand of DNA is split down the middle and forms two, identical copies. ... A replication bubble is an unwound and open region of a DNA helix where DNA replication occurs. Helicase unwinds only a small section of the DNA at a time in a place called the origin of replication
What is the function of telomerase?
Telomerase is the enzyme responsible for maintenance of the length of telomeres by addition of guanine-rich repetitive sequences. Telomerase activity is exhibited in gametes and stem and tumor cells.
What is the fundamental unit of DNA?
The basic unit used to make a strand of DNA is called a nucleotide. A single basic unit or "building block" of DNA consists of a sugar , a phosphate group and a base. Sugars are rings of carbon and oxygen atoms.
What did the Meselson-Stahl experiment seek to determine.
The experiment done by Meselson and Stahl demonstrated that DNA replicated semi-conservatively, meaning that each strand in a DNA molecule serves as a template for synthesis of a new, complementary strand
What is the leading strand during replication? The lagging strand? Which one is more efficient?
The leading strand is synthesized continuously, as shown in Figure 5. In contrast, the lagging strand is synthesized in small, separate fragments that are eventually joined together to form a complete, newly copied strand.
What are telomeres?
The telomeres are special structures on the chromosome ends that are essential for providing protection from enzymatic end-degradation and maintaining chromosomal and genomic stability
What were the results of the Meselson-Stahl experiment? How did they support the semiconservative hypothesis?
This result is consistent with the semiconservative replication model, which predicts that all DNA molecules will consist of one 15N-labeled DNA strand and one 14N-labeled DNA strand.
What are the bonds between nucleotides are called?
When nucleotides are incorporated into DNA, adjacent nucleotides are linked by a phosphodiester bond: a covalent bond is formed between the 5' phosphate group of one nucleotide and the 3'-OH group of another (see below). In this manner, each strand of DNA has a "backbone" of phosphate-sugar-phosphate-sugar-phosphate.