8.1- GENES AND THE GENETIC CODE Flashcards
What is a gene?
section of DNA that contains coded information for making polypeptide + functional RNA
What is the coded information in the form of in a gene?
specific sequence of bases along DNA molecule
What do polypeptides make up?
proteins
As polypeptides make up proteins, what do genes determine?
genes determine proteins of organism
What are enzymes an example of?
proteins
What do enzymes control?
control chemical reactions
As enzymes control chemical reactions, what are they responsible for?
organism’s development + activities
What determines the nature + development of all organisms?
genes + environmental factors
What is the particular position of a gene on a section of DNA called?
locus
What can a gene code for? (2)
amino acid sequence of polypeptide
or
functional RNA, including ribosomal RNA + transfer RNAs
How many genes does one DNA molecule carry?
carries many genes
Why did scientists suggest there must be a minimum of three bases that codes for each amino acid: number of amino acids?
only 20 different amino acids regularly occur in proteins
Why did scientists suggest there must be a minimum of three bases that codes for each amino acid: what each amino acids must have?
each amino acid must have its own code of bases on DNA
Why did scientists suggest there must be a minimum of three bases that codes for each amino acid: number of bases?
only 4 different bases (adenine, guanine, cytosine + thymine) present in DNA
Why did scientists suggest there must be a minimum of three bases that codes for each amino acid: what if each base coded for a different amino acid?
if each base coded for a different amino acid, only 4 different amino acids could be coded for
Why did scientists suggest there must be a minimum of three bases that codes for each amino acid: what if a pair of bases were used for an amino acid?
using pair of bases, 16 (4^2) different codes possible, which is still inadequate
Why did scientists suggest there must be a minimum of three bases that codes for each amino acid: what if three bases were used for an amino acid?
three bases produces 64 (4^3), more than enough to satisfy requirements of 20 amino acids
As the code has three bases for each amino acid, what is each one called?
a triplet
As there are 64 possible triplets and only 20 amino acids, what follows?
some amino acids coded for by more than one triplet
What are a few amino acids coded for by?
only a single triplet
What are most of the amino acids coded for by?
between two and six triplets each
Why is the code known as a ‘degenerate code’?
most amino acids coded for by more than one triplet
How is a triplet always read?
in one particular direction along the DNA strand
What is the start of a DNA sequence always?
code for polypeptide always same triplet
What does the start the DNA sequence triplet code for?
amino acid methionine
What happens if the first methionine molecules doesn’t form part of the final polypeptide?
it’s later removed
What do three triplets that do not code for an amino acid called?
‘stop codes’
What do ‘stop codes’ mark?
end of polypeptide chain
What does it mean that the code is non-overlapping?
each base in sequence read only once
What does it mean the code is universal?
with a few minor exceptions each triplet codes for same amino acid in all organisms
What is the code being universal indirect evidence for?
evolution
What does much of the DNA in eukaryotes not do?
do not code for polypeptides
What are coding sequences called?
exons
What are non-coding sequences called?
introns
What do some genes code for?
ribosomal RNA + transfer RNAs
