✅8 - DNA, Genes and Protein Synthesis Flashcards
What is a gene?
A section of DNA that contains the coded information for making polypeptides and functional RNA
What is a locus?
The particular positions of a gene in a section of DNA
Why was it suggested that there were a minimum of three bases coding for each amino acid?
Only 20 amino acids occur in proteins
Each amino acid must have its own code
There are only four bases
4^2 is 16, while 4^3 is 64 amino acids
Why is the code degenerate?
Because most amino acids are coded for by more than one triplet
How is the triplet always read?
In one direction
What is always the first triplet in an amino acid sequence?
That coding for the amino acid methionine
Why is the code non-overlapping?
Because each base sequence is only read once, as triplets rather than individually
Why is the code universal?
Because with a few minor exceptions each triplet codes for the same amino acid in all organisms - indirect evidence for evolution
What are introns?
Triplets which do not code for any amino acids
What are exons?
Triplets that are expressed
What are histones?
Proteins associated with DNA
What is a chromatid?
A thread of DNA which makes up a chromosome
What are homologus pairs?
One chromosome from each parent in a pair, with the same genes but not necessarily the same alleles
What is the human chromosome number?
46
What is an allele?
One of a number of alternative forms of a gene
What is mRNA?
Messenger RNA
What is the relative size of mRNA?
Small enough to leave the nucleus through the nuclear pores and to enter the cytoplasm
What is a codon?
A sequence of three bases on mRNA that codes for a single amino acid
What is a genome?
The complete set of genes in a cell, including those in mitochondira and/or chloroplasts
What is a proteome?
The full range of proteins produced by the genome
What is RNA made up of?
Ribose
One organic base
A phosphate group
What are the two types of RNA important to protein synthesis?
mRNA
tRNA
What is the base sequence of mRNA determined by?
The sequence of bases on DNA
What are the complementary base pairings for RNA?
C + G
A + T/U
What is transcription?
When a complementary section of part of the DNA sequence is made in the form of a molecule of pre-mRNA
What is translation?
The mRNA is used as a template to which complementary tRNA molecules attach and the amino acids they carry are linked to form a polypeptide
How is mRNA made from pre-mRNA?
Through splicing
Which enzyme builds the pre-mRNA strand?
RNA polymerase
Why do mRNA molecules leave the nucleus via nuclear pores?
Because they are too large to diffuse out
Where does the ribosome attache to?
The starting codon at the end of the mRNA molecule
Where does the tRNA molecule move to?
The ribosome, and attaches to the complementary codon on the mRNA
How many tRNA molecules does the ribosome bring together at once?
Two
What is used to form peptide bonds between the two amino acids?
An enzyme and ATP
What happens as the third amino acid is attached to the sequence?
The first tRNA is released and it is free to collect another amino acid
How many ribosomes can pass behind the first?
Up to 50