Before DNA can be replicated, the double stranded molecule must be “unzipped” into two single strands. DNA has four bases called adenine (A), thymine (T), cytosine (C) and guanine (G) that form pairs between the two strands. Adenine only pairs with thymine and cytosine only binds with guanine. In order to unwind DNA, these interactions between base pairs must be broken. This is performed by an enzyme known as DNA helicase. DNA helicase disrupts the hydrogen bonding between base pairs to separate the strands into a Y shape known as the replication fork. This area will be the template for replication to begin.
Step 2: Primer Binding
The leading strand is the simplest to replicate. Once the DNA strands have been separated, a short piece of RNA called a primer binds to the 3' end of the strand. The primer always binds as the starting point for replication. Primers are generated by the enzyme DNA primase.
Step 3: Elongation
Enzymes known as DNA polymerases are responsible creating the new strand by a process called elongation. There are five different known types of DNA polymerases in bacteria and human cells. In bacteria such as E. coli, polymerase III is the main replication enzyme, while polymerase I, II, IV and V are responsible for error checking and repair. DNA polymerase III binds to the strand at the site of the primer and begins adding new base pairs complementary to the strand during replication. In eukaryotic cells, polymerases alpha, delta, and epsilon are the primary polymerases involved in DNA replication. Because replication proceeds in the 5' to 3' direction on the leading strand, the newly formed strand is continuous.
Step 4: Termination
Once both the continuous and discontinuous strands are formed, an enzyme called exonuclease removes all RNA primers from the original strands. These primers are then replaced with appropriate bases. Another exonuclease “proofreads” the newly formed DNA to check, remove and replace any errors. Another enzyme called DNA ligase joins Okazaki fragments together forming a single unified strand. The ends of the linear DNA present a problem as DNA polymerase can only add nucleotides in the 5′ to 3′ direction. The ends of the parent strands consist of repeated DNA sequences called telomeres. Telomeres act as protective caps at the end of chromosomes to prevent nearby chromosomes from fusing.
So if that here are the functions of enzymes used:
DNA helicase - unwinds and separates double stranded DNA as it moves along the DNA. It forms the replication fork by breaking hydrogen bonds between nucleotide pairs in DNA.
DNA primase - a type of RNA polymerase that generates RNA primers. Primers are short RNA molecules that act as templates for the starting point of DNA replication.
DNA polymerases - synthesize new DNA molecules by adding nucleotides to leading and lagging DNA strands.
Topoisomerase or DNA Gyrase - unwinds and rewinds DNA strands to prevent the DNA from becoming tangled or supercoiled.
Exonucleases - group of enzymes that remove nucleotide bases from the end of a DNA chain.
DNA ligase - joins DNA fragments together by forming phosphodiester bonds between nucleotides.
Have a nice day
Answer:
The first statement
Explanation:
Osmosis is the transfer of water molecules from a low concentration to a higher concentration through a partially permeable membrane
The partially permeable membrane only allows water molecules to pass through
Therefore, the first statement best describes osmosis
Let us assign the
recessive allele for freckle to be f and
the dominant F. According to the statement, we deduce that ff = 0.04.
The frequency of the recessive f allele is, therefore, is
0.2 (square root of 0.04 ).
Hardy-Weinburg p + q = 1
P + 0.2 = 1; p = 1- 0.2 = 0.8
Therefore using the Hardy-Weinburg equation of a population
in equilibrium
P2+2pq+q2=1
Heterozygous individuals are;
2pq = 2*0.8*0.2 = 0.32
This is 32% of the population
Answer:
The basement membrane or basal lamina on which the epithelium form, made by extracellular matrix.
Explanation:
The basement membrane is the layer underlies all epithelia that is made up extracellular matrix secreted by the epithelium cells that provide structural support to the structure of epithelia.
It forms the barrier between epithelial tissues therefore once a epithelial cancer penetrate this basement membrane it will spread to all underlying tissues.
Thus, the correct answer is - The basement membrane or basal lamina on which the epithelium form, made by extracellular matrix.
The basement membrane is form of extracellular matrix that underlies all epithelia. It provides structural support to epithelia and forms a mechanical connection between epithelia and underlying connective tissue.
The basement membrane, or basal lamina, is a sheet of proteins and other substances to which epithelial cells adhere and that forms a barrier between tissues.
Epithelial cancers may have the ability to penetrate through the basement membrane and spread to underlying tissues.
