Genes Flashcards
What is a nucleotide made up of?
A phosphate group, a carbon sugar molecules and 1 of 4 nitrogenous bases.
What is the structure of DNA?
2 complementary anti parallel chains of nucleotides
What is the difference between the 5’ and 3’ end?
The 5’ end is the end where the 5th carbon on the sugar molecule is at the end of the chain whereas the 3’ end is where the 3rd carbon on the end sugar molecule is at the end
Why is DNA described as universal?
All 4 nitrogen base pairs are found in the DNA of every living thing
What are the 4 base pairs in DNA?
Cytosine, thymine, adenine and guanine
How would you tell the difference between cytosine and adenine?
Adenine is a purine and hence has 2 rings where as cytosine is a pyrimidine and only has 1 ring
How would you tell the difference between adenine and guanine
Guanine has an oxygen in it whereas adenine doesn’t. Guanine also forms 3 H bonds instead of adenines 2
What bases are pyrimidines?
Cytosine, uracil and thymine
What bases are purines?
Adenine and guanine
What base does adenine pair with in DNA?
Thymine
What base does guanine pair with?
Cytosine
What are each bases complementary pairing in DNA?
G and C (3 H bonds)
A and T (2 H bonds)
What base does uracil pair with?
Adenine
How is RNA different to DNA?
It is only single stranded, contains a ribose sugar molecule and has uracil in place of thymine
What is tRNA?
Transfer RNA, which brings amino acids to the ribosomes
What is mRNA?
Messenger RNA, it is a copy of the template strand of DNA that codes for proteins
What is rRNA?
Ribosomal RNA, structural component of a ribosome
How are nucleotides joined together?
Through nucleotide polymerisation, a nucleotide triphosphate will bind to the 3’ end of a DNA chain and 2 of its phosphate molecules are posed in the process
What is the first step of transcription?
RNA polymerase binds to a promoter region on gene which causes the DNA to unwind
What does RNA polymerase do?
Unwinds the DNA and moves along its template strand creating an RNA strand by adding complementary bases of the template strand together.
How is transcription terminated?
When the RNA polymerase reaches the terminator section on a gene
What occurs during splicing?
Introns are cut out of the gene so only the Exons remain
What are exons?
The part of the pre mRNA strand that carry the coding information
What end is the poly(A) tail added to?
The 3’ end
What end is the methylated cap added to?
The 5’ end
Why are pre mRNA strands capped?
So the strands can thread through ribosomes
Why Do pre mRNA strands undergo polydenylation?
So they are provided with protection and to assist in movement
What direction does RNA polymerase go in along the template strand?
5’ to 3’
What occurs during transcription?
DNA is copied to form RNA
What occurs during translation?
Proteins are synthesised from RNA in ribosomes
What end of the mRNA enters the ribosome first?
The 5’ end (the cap)
How are proteins synthesised in a ribosome?
tRNA brings in amino acids and if its has an anticodon complementary to the codon of the mRNA the amino acid will stay behind to form part of the polypeptide chain.
How does transcription stop?
When the ribosome reaches a stop codon on the mRNA the polypeptide chain is released
What is a codon?
A set of 3 bases that codes for a specific amino acids
What is the genetic code?
The set of rules that defines info in mRNA sequences is translated into amino acids
How many codon combinations are there?
64
How many amino acids are there?
20
What is the start codon?
AUG
What are the three stop codons?
UAA, UAG, UGA
Why the genetic code described as degenerate?
Because multiple codons can code for the same thing, that is there are more codon combinations then there are amino acids
Why is the genetic code universal?
Because it is the same code used for all living things
What is a structural gene?
A gene that codes for proteins which will assist in the structure and function of an organism
What is a regulator gene?
A gene that codes for a protein that will assist in gene regulation
What is the difference between prokaryotic and eukaryotic protein synthesis?
Prokaryotic transcription and translation occur almost simultaneously as they both occur in the cytosol
Not post transcriptional modifications are made to mRNA
What is an operon?
A group of genes that all have the same function, and are transcribed together as they share the same promoter and operator
H
Why is the lac operon important for Bacteria?
It allows them to rapidly adjust to their environment and not waste excess resources
