Unit 6,nucleic Acids And Proteien Synthesis Flashcards
Describe the 5 main steps in transcription
1)DNA helicase breaks the hydrogen bonds between complimentary bases, on a section of the dna molecule where the gene is located
2)only of the strands, the template or antisense strand is sued to make the mRNA, which runs from 3’ to 5’
3)free activated mRNA nucleotides pair with complimentary base pairs on the antisense/template strand by hydrogen bonds( the sequence will be the same as the sense/non transcribed strand and will contain urcail instead of thymine)
4)RNA polymerase then catalyses the reaction(also runs in 3’to 5’) and bonds together the RNA nucleotides through phosphodiester bonds to form the sugar phosphate backbone of the MRNA molecule
5)once the gene has been transcribed, hydrogen bonds break between the mRNA and dna, and the gene leaves the nucleus through a pore in the nuclear envelope
What is mRNA called before post transcription modification, and what is it called after
Pre-mRNA molecule or primary transcript
And after it is called mature mRNA
What occurs during post transcription modification, or splicing
-during transcription of a gene, both introns(non-coding dna) and extrons(coding dna) are transcribed, so the pre-mRNA mocleule contains both
-but the introns are not to be translated, so they are remove as exons fuse together to form a continuous mRNA molecule
Which type of organisms does post transcription mopdoftcaion occur in
Only in eukaryotic organisms. Bc they contain both introns( noncoding dna) and exons(coding dna)
(So does not occur in prokaryotic organisms)
Explain the steps of transcription
1)dna hélicase breaks hydorgen bonds between complimentary base pairs in double helix, this unwinds dna strand to form two polynutlceotide strands which act as template strands
2)free floating dna nuelcotide trphosphates are attracted to comoplmetary base pairs on the template strands
3)dna polymerase creates phosphodester bonds between nucleotides through condensation reactions
Between deoxyribose sugars and phosphate groups of adjacent nucleotides
4)dna polymerase only builds in the 5 prime to 3 rime direction, and so towards the replication fork.
So attaches to the 3 prime end of the orignal strand to create a leading strand
5)on the other strand it attaches to the 5 prime ends and so forms short fragments called Okazaki fragments.
6)dna ligase joins Okazaki fragments together through phosphpdister bonds on the lagging strand
7)2 genetically idnetcial, dna molecules are produced, and process is semi conservative bc one of ecah strand is form old organs strand
What direction does dna polymerase move in dna replication
5’ to 3’
What is an Okazaki fragment
Short strands of dna formed from the discontinuous sysnethsis of dna during dna replication.
Bc dna polymerase can only move in 5’ to 3’ direction, and so when it attaches to the 5’ end of the orinal template strand, it sysnethises the strand discontinuolsy
Role of dna ligase in dna replication
Catalyses formation of phosphpdtser bonds during dna replication between Okazaki fragments on the lagging strand
How many molecules of dna produced form dna replication
2 molecules
Where ecah new molecule has one strand from original dna 9one of the template strands) and one strand that is newly made
Role of dna helicase in dna replication
Break hydorgen bons between complimentary base pairs between 2 strands of the double helix,
To unwind the dna strand and form 2 polynttulcotide chians (that act as template strands)
Give 6 differences between dna and rna
-dna is longer molecule than rna, rna is shorter
-dna is double helix so double stranded, rna is single stranded
-dna has adenine, thymine, guanine, cytosine. RNA has adenine uracil guanine and cytosine
-dna has ratio of purine to pyramidines 1;1. But rna has ratio variable
-dna has deoxyribose sugar, rna has ribose sugar only
