3.4.1 DNA, Genes and Chromosomes Flashcards
Describe DNA molecules in prokaryotic cells?
Short
Circular
Not associated with proteins
How does protein synthesis differ in prokaryotic and eukaryotic cells?
Transcription occurs in the nucleus in a eukaryotes; transcription occurs in the cytoplasm of a prokaryote
Translation occurs in the cytoplasm of eukaryotes and prokaryotes
Where is DNA found in prokaryotic cells?
Loose in the cytoplasm
Where is DNA found in eukaryotic cells?
In a membrane bound nucleus
In what form is the DNA in a prokaryotic and eukaryotic cell?
Prokaryotic- a single loop (with plasmids)
Eukaryotic- linear chromosomes
Is the DNA is prokaryotic and eukaryotic cells associated with proteins?
Prokaryotic- no (not a chromosome)
Eukaryotic- yes, wrapped around histones
What is the length of the DNA molecules in a prokaryote and eukaryotes?
Prokaryote- shorter
Eukaryote- longer
Where is DNA found in eukaryotic cells?
Nucleus
Mitochondria
Chloroplasts
How is DNA thought to have got into mitochondria and chloroplasts?
Endosymbiotic theory
Mitochondria and chloroplasts were once free living prokaryotes that were engulfed by a cell
Define chromosome.
Thread like structure found in the nucleus of eukaryotic cells
Consists of a single molecule of DNA
Highly wound around protein molecules called chromatin
What is a gene?
A section of DNA that codes for the amino acid sequence of one polypeptide
What is a locus?
The position on a particular chromosome where you find a gene
What is a homologous pair?
Chromosome pairs
One from each parent
Similar in length, gene position and centromere location
How many pairs of chromosomes does a human have?
23
What is an allele?
The different forms a gene can take
Define diploid.
A cell that contains two sets of chromosomes
What is a diploid number?
The number of chromosomes in a cell
Abbreviated to 2n (where n is the number of chromosomes)
Define homozygous.
Where both alleles for a gene are the same
Define heterozygous.
Where the alleles for a gene are different
What does it mean if a cell is haploid?
Contains one complete set of chromosomes
Give an example of a haploid cell?
Gametes
When are haploid cells produced?
Meiosis
What is the haploid number?
Number of chromosomes within the cell that is the set
Define genome.
The full set of genes in a cell
Define proteome.
The full range of proteins coded for by the genes
Define karyotype.
The number and appearance of chromosomes in the nucleus of a eukaryotic cell
Why isn’t DNA stored in the nucleus of a prokaryotic cell?
They have no nucleus!
What is the purpose for the cooling of DNA in a chromosome?
So it is easy to separate/ unravel DNA without damaging it
For DNA replication
Describe the structure of a chromosome.
A DNA double helix strand forms a chromatin fibre
This wraps around histone proteins
Histone proteins coil to make a chromatin fibre
These form loops
Loops form rosettes
These coil together
One chromatid is 10 coils long
Define exon.
Sequences of bases in a gene that code for a sequence of a amino acids in a protein
Define intron.
Non-coding DNA which can be found between genes in multiple repeats or within genes
Why is DNA a ‘universal code’?
DNA is used in virtually all organisms as the material of inheritance
What is a codon?
The sequence of three bases that codes for one amino acid
What is degenerate code?
Amino acids are coded for by more than 1 codon
What makes DNA ‘non-overlapping’?
Each base in the sequence is read only once so the code is non-overlapping
Why are three bases needed to core for each amino acid?
There are 4 bases
If one base coded for one amino acid there would only be 4 possibilities
If they were in pairs there would only be 16 possibilities
We need 20 different codes
With 3 bases there are 64 possible combinations
What is an advantage to a cell of having degenerate code?
If there is a substitution mutation in the third base of a codon, the impact will be small on the amino acid made
(eg GGA and GGG codes for the same thing)
Which bases are involved in the triplet code table?
ATGC
Ow many amino acids would be coded for from AAACACTTGGTC?
4
What do polypeptides combine to produce?
Proteins
