Nucleotides And Nucleic Acids 2.3 Flashcards
What is the role of helicase in DNA replication
-an enzyme that catalyses the breaking of hydrogen bonds between the nitrogenous bases in a DNA molecule
What is the role of DNA polymerase in DNA replication?
-enzyme that catalyses the formation of phosphodiester bonds between the nucleotides ,to form DNA
Why is DNA replication described as semi-conservative ?
One old strand is conserved in each new molecule.
Describe the process of semi-conservative DNA replication
1- the double helix is UNTWISTED a bit at a time this is catalysed by a gyrase enzyme
2-DNA unzips- hydrogen bonds between the nucleotide bases are broken. This is catalysed by HELICASE and results in two single strands of DNA with exposed nucleotide bases
3-free PHOSPHORYLATED NUCLEOTIDES present in the nucleoplasm in the nucleus , are bonded to the exposed bases , following complementary base pairing rules
4-DNA POLYMERASE catalyses the addition of new nucleotide bases in the 5’ to 3’ direction to the single strands of DNA , it uses each single strand of unzipped DNA as a template
5- the LEADING strand is synthesised continuously whereas the LAGGING strand is in fragments (discontinuous) that are later joined (this is catalysed by ligase)
6-HYDROLYSIS of the activated nucleotides to release the extra phosphate groups supplies the energy to make PHOSPHODIESTER bonds between the sugar residue of one nucleotide and the phosphate group of the next nucleotide
Two identical strands of DNA are formed.Both containing half of the original material.
What is the role of DNA ligase?
-an enzyme that joins the nucleotides together in sections
How are the number of mutations during DNA replication limited?
During DNA replication there are enzymes that can proofread and edit out incorrect nucleotides
What are some examples of spontaneous gene mutations?
•Base substitution – a nucleotide base is replaced with another
•Base deletion – a nucleotide base is deleted from the sequence
•Base insertion – a nucleotide is inserted into the sequence
State what structural detail of a polypeptide is altered by gene mutations
The sequence of amino acids (Primary structure)
Why is the genetic code universal?
-almost every organism uses the same code
Why is the genetic code described as degenerate?
. multiple codons can code for the same amino acid
.this can limit the effect of mutations
Describe the process of transcription
• DNA HELICASE breaks the hydrogen bonds between the bases in the two strands of DNA.
• This causes the DNA helix to unwind and one strand acts as a template.
•Free mRNA nucleotides align opposite exposed complementary DNA bases
• The enzyme RNA POLYMERASE joins together the adjacent RNA nucleotides, forming phosphodiester bonds, to create a new mRNA polymer chain.
• Once one gene is copied, the mRNA is modified and then leaves the nucleus through the nuclear envelope and attaches to a ribosome
What is transcription?
The process in which a complementary mRNA copy of one gene on the DNA is created in the nucleus
Describe the process of translation
-tRNA molecules bring the amino acids and find their place when their anticodon binds by temporary hydrogen bonds to the complementary codon on the mRNA molecule
-as the ribosome moves along the length of mRNA it reads the code and when 2 amino acids are adjacent to each other a peptide bond forms between them (ATP provides energy for this)
-the ribosome will move along the mRNA molecule to the next codon and another complementary tRNA will attach to the next codon on the mRNA
-this continues until the ribosome reaches the stop codon at the end of the mRNA molecule causing the ribosome to detach
The polypeptide chain is now created and will enter the Golgi body for folding and modification
What replaces Thymine in RNA?
Uracil
What is the start codon?
AUG
-codes for amino acid methionine