Genes and chromosomes

Question 1

What is a gene?

Answer 1

A section of DNA at a locus ( a particular position) that contains the coded information for making the amino acid sequences of polypeptides and functional RNA. This coded information is in the form of a specific sequence of bases along the DNA molecule

Question 2

Describe what the genetic code is

Answer 2

There must be a minimum of 3 bases that code for each amino acid, and this was found out because there are only 20 amino acids that occur in proteins, and each amino acid must have its own code of bases on the DNA and there are only 4 different bases existing in DNA A,C,T
,G and if each base coded for a different amino acid only 4 amino acids would be coded for, so using a pair of bases would code 16 amino acids (4 sqaured) which is not enough to satisfy the 20 amino acids that already exist however 3 bases produce 64 which is more than enough to satisfy the 20 amino acids that are present

Question 3

Describe what is meant by the degenerate code

Answer 3

-Multiple codons can code for the same amino acid during protein synthesis.
- A single codon cannot code for more than one amino acid

Question 4

What is meant by the genetic code being universal

Answer 4

All species use the same 4 bases A,T,C,G and each base sequence codes for the same amino acid in all sequences

Question 5

What is meant by the genetic code being non overlapping

Answer 5

This refers to how the code is read, the first 3 bases are read as one codon then the next 3 are the second etc , each base is read only once and dont overlap

Question 5

Describe what an extron is

Answer 5

These are regions of the gene that are coding, they contain the codons that are later read to make proteins, each codon of an exon specifies a certain amino acid, the sequence of codons in the exons determine the sequence of amino acids in a polypeptide

Question 6

Describe what an intron is

Answer 6

Regions of the gene that do not contain codons that are needed to make the final protein

Question 7

What is the difference between dna in eukaryotic cells and prokaryotic cells

Answer 7

In prokaryotic cells the DNA is short and circular and are not assosiated with DNA meaning they do not have chromosomes
In eukaryotic cells the DNA molecules are long and linear and are associated with histones to form chromosomes

Question 8

Describe how the structure of a chromosome is formed

Answer 8

There is a DNA molecule and this is combined with protein molecules, then this DNA histone complex is coiled and this coils coil to form loops, then these loops coil and pack together to form chromosomes meaning alot of DNA can fit into one chromosome

Question 9

What is an allele

Answer 9

One of a number of alternative forms of a gene, a different version of it. Each individual inherits an allele from each parent and they may be the same or different