8.2- DNA AND CHROMOSOMES Flashcards
What are the two types of cells?
prokaryotic cells
eukaryotic cells
What are the DNA molecules of prokaryotic cells i.e. bacteria like? (3)
shorter
form circle
not associated with protein molecules
Do prokaryotic cells have chromosomes?
no
What are the DNA molecules of eukaryotic cells like? (3)
longer form line (linear) occur in association with proteins called histones to form structures called chromosomes
What in eukaryotic cells also contain DNA? (2)
mitochondria
chloroplasts
What is the DNA of the mitochondria + chloroplasts in eukaryotic cells like? (3)
short
circular
not associated with proteins
When are chromosomes only visible as distinct structures?
when cell dividing
How are the chromosomes for the time that the cell is not dividing?
widely dispersed throughout nucleus
How do the chromosomes appear when they first become visible at the start of cell division?
chromosomes appear as two threads, joined at single point
What is each thread called? (chromosomes appear as two threads, joined at single point)
chromatid
Why is each thread called a chromatid?
as DNA has already replicated to give two identical DNA molecules
What is the DNA in chromosomes held by?
histones
What is done to the considerable length of DNA found in each cell?
highly coiled + folded
What sort of helix is DNA?
double helix
What is done the DNA helix to fix it in position?
helix wound around histones to fix it in position
What happens to the DNA-histone complex?
it’s then coiled
What happens after the DNA-histone complex is coiled?
looped + further coiled before being packed into chromosome
What can happen as the DNA-histone complex is coiled + looped + further coiled before being packed into chromosome?
a lot of DNA is condensed into a single chromosome
How many DNA molecules does does a chromosome contain?
a single molecule of DNA
What does a single molecule of DNA have along its length?
many genes
What does each gene occupy?
specific position (locus) along DNA molecule
In most species, what sort of number of chromosomes are in the cell of adults?
even number of chromosomes
What are sexually produced organisms the result of?
fusion of sperm + egg, each of which contributes one complete set of chromosomes to offspring
What is one of each pair of chromosome derived from in sexually produced organisms?
one of each pair derived from chromosomes provided by mother in egg (maternal chromosome) + other derived from chromosomes provided by father in sperm (paternal chromosomes)
What are the pair of chromosomes known as?
homologous pairs
What is the total number of chromosomes referred to as?
diploid number
What is the diploid number in humans?
46
What is a homologous pair always?
always two chromosomes that carry same genes but not necessarily same alleles of genes
What happens to chromosomes number in meiosis?
halving of number of chromosomes
What is the way that meiosis done ensure?
each daughter cell receives one chromosomes from each homologous pair
What does it mean as each daughter cell receives one chromosomes from each homologous pair from meiosis?
each cell receives one gene from each characteristic of organism
What happens when the haploid cells combine?
diploid state, with paired homologous chromosomes restored
What is an allele?
one of number of alternative forms of gene
How many different forms does each gene exist in?
two, occasionally more
What is the different forms a gene exists in called?
gene
Where does each individual inherit one allele from?
each of its parents
Can the alleles inherited from the parents be the same or different?
may be same or different
What is each allele like if an individual inherits different alleles?
each allele has different base sequence , so different amino acid sequence, so produces different polypeptide
What is a mutation?
change in base sequence of gene producing new allele of that gene
What does a mutation result in (hint- amino acids)
different sequence of amino acids being coded for
From a mutation, what will the different sequence of amino acids being coded for lead to?
production of different polypeptide + hence different protein
What happens sometimes with the different protein produced from a mutation?
different protein may not function properly or may not function at all
When the different protein produced from a mutation is an enzyme, what can happen?
may have different shape
If the different protein produced from a mutation is an enzyme and it has a different shape, what may happen?
new shape may not fit enzyme’s substrate
What happens if the new shape may not fit enzyme’s substrate due to mutation?
enzyme may not function + this can have serious consequences on organism
