4.1 DNA genes and chromosomes Flashcards
What is a gene
A base sequence of DNA that codes for a specific polypeptide or functional RNA
What is the name given to the position of a particular gene on a chromosome
Locus
What is an allele
Different form of a gene
e.g. eye colour
How many alleles form one gene
2, one from father and one from mother
List 3 differences between prokaryotic and eukaryotic DNA
- Prokaryotic DNA is circular whereas eukaryotic DNA is linear
- Eukaryotic DNA is associated with histone proteins whereas prokaryotic DNA isn’t
- Prokaryotic DNA is shorter than eukaryotic DNA
How many chromosomes are in a human cell
46
How are chromosomes formed
The DNA wraps around histone proteins, continuous coiling results in a supercoil and further folding results in a chromosome
What does karyotype mean
The number and the type of chromosomes in a cell
What are homologous chromosomes
2 chromosomes with the same genes in the same loci
Can haploids have homologous chromosomes
No
What is the genetic code
The sequence of bases in DNA
If one base=one amino acid, what is the possible number of amino acids
4
If 2 bases= one amino acid, what is the possible number of amino acids
16
If 3 bases= one amino acid, what is the possible number of amino acids, and what does this show
64, there are only 20 naturally occurring amino acids therefore showing that some amino acids have multiple codes
What are the 3 features of the genetic code
- Universal
- Degenerate
- Non-overlapping
How is the genetic code universal
The triplet that codes for one amino acid in one organism will code for the same amino acid in all organisms
How is the genetic code degenerate
Each triplet codes for a specific amino acid, many amino acids have more than one code
How is the genetic code non-overlapping
Each base is only read once
What are introns
Non-coding regions of DNA
What are exons
Coding regions of DNA
What type of DNA, eukaryotic or prokaryotic, contains introns
Eukaryotic
In what process are the introns in DNA cut out
Protein synthesis
What is a genome
The entire genetic code of an organism
What is a proteome
The entire set of proteins that can be produced by the genome
What does mRNA carry
The code for one gene
Why can mRNA fit out of the nuclear pores but DNA cannot
Because mRNA only carries the code for one gene and is single stranded whereas DNA carries the genetic code for all genes and is double stranded so too large to fit through the pores
What are the series of 3 consecutive bases called in DNA
A triplet
What are the series of 3 consecutive bases called in mRNA
A codon
What are the series of 3 consecutive bases called in tRNA
An anticodon
What shape is the polynucleotide of mRNA
Helical
What is the name of the process when mRNA copied from DNA
Transcription
As mRNA is copied from DNA, what is complementary to what
mRNA’s codons are complementary to DNA’s triplets
What is the shape of a tRNA molecule
Cloverleaf shape
Is tRNA single or double stranded
Single
How is the cloverleaf shape of a tRNA molecule held in place
By hydrogen bonds between the bases
What is the function of tRNA
To transfer amino acids
In a tRNA molecule what is the name of the 3 exposed bases at the top
The amino acid attachment site
What is the function of rRNA
It combines with proteins to make ribosomes
Describe how the appearance of the area containing DNA in a TEM image of a eukaryotic cell would differ from a prokaryotic cell (2 marks)
- Nucleus
- Nucleolus
- Mitochondria contain DNA
