3.4 Topic 4 - 3.4.1 DNA, genes and chromosomes Flashcards
What is a gene?
A section of DNA (sequence of DNA bases) that contains the coded information for making polypeptides and functional RNA.
What form is the coded information in genes of?
A specific sequence of bases along the DNA molecule.
What do genes determine?
Genes determine the proteins of an organism.
What are enzymes and what are they responsible for?
Proteins and as they control chemical reactions they are responsible for an organism’s development and activities.
Overall, what is a gene?
A gene is a section of DNA located at a particular position (locus = fixed position) on a DNA molecule.
The gene is a base sequence of DNA that codes for…
… the amino acid sequence of a polypeptide.
… or a functional RNA, including ribosomal RNA and transfer RNAs.
Does one DNA molecule carry many genes?
Yes.
DNA codes for amino acids but it is made up of …
… nucleotides not amino acids.
Each amino acid is coded for by a sequence of 3 bases in a gene called a triplet.
What is the minimum suggested number of bases that code for an amino acid?
3.
How many different amino acids occur in proteins?
20.
Each amino acid must have its own code of bases on the DNA. True or false?
True.
How many different bases are there?
4.
What are the 4 different bases?
Adenine, Guanine, Cytosine & Thymine.
How many bases produce 64 different codes?
- 4 different bases and 3 bases code for an amino acid.
How many possible triplets is there?
64.
What does it mean why you say ‘The genetic code is non-overlapping?’
Each base in the sequence is only read once, separate from the triplet before it and after it. Base triplets do not share their bases.
What does it mean why you say ‘The genetic code is degenerate?’
Most amino acids are coded for by more than one base triplet.
There are more possible combinations of triplets than there are amino acids (20 compared to 64 possible triplets).
What does it mean why you say ‘The genetic code is universal?’
Each specific base triplet codes for the same amino acid in all living organisms.
A triplet is always read in one particular direction along the DNA strand. True or false?
True.
What is the amino acid which is at the start of a DNA sequence that codes for a polypeptide?
It is always the same triplet. This codes for the amino acid methionine.
How many triplets do not code for any amino acid? and why?
- These are called ‘stop codes’ and mark the end of a polypeptide chain.
What is the genetic code?
The sequence of base triplets (codons) in mRNA which codes for specific amino acids.
What is the word which describes how genes can exist in more than one form?
Alleles.
Describe the DNA in prokaryotic cells:
DNA molecules are shorter, form a circle and are not associated with proteins called histones. The DNA condenses to fit in the cell by supercoiling.