3.4.1 - DNA, genes and chromosomes Flashcards
how is DNA stored in eukaryotic cells?
eukaryotic cells have linear DNA molecules that exist as chromosomes
describe chromosomes
thread-like structures, each made up of 1 long molecule of DNA and its associated proteins
where are chromosomes found in eukaryotic cells
chromosomes are found in the nucleus
in eukaryotic cells, what are DNA molecules wound around
the DNA molecule is really long so has to be wound up so it can fit in the nucleus, it’s wound around proteins called histones
in eukaryotic cells what do histone proteins help do
histone proteins help to support the DNA, the DNA (and protein) is then coiled up very tightly to make a compact chromosome
what organelles in eukaryotic cells also have DNA?
mitochondria and chloroplasts also have their own DNA
what is the DNA in mitochondria and chloroplasts like?
similar to prokaryotic DNA as it’s circular/shorter than DNA molecules in the nucleus and isn’t associated with histone proteins
what do prokaryotes carry DNA as?
prokaryotes carry DNA as chromosomes
what is different about the DNA in prokaryotes compared to eukaryotes
the DNA molecules are shorter and circular, the DNA isn’t wound around any histones and condenses to fit in the cell by supercoiling
what does DNA contain?
genes
what is a gene
a gene is a base sequence of DNA that code for the amino acid sequence of a polypeptide or a functional RNA (including ribosomal RNA and tRNAs)
what differs different polypeptides
different polypeptides have a different number and order of amino acids
what determines the order of amino acids in a polypeptide
the order of bases in a gene determines the order of amino acids in a particular polypeptide
what is each amino acid coded for by?
each amino acid is coded for by a sequence of 3 bases in a gene called a triplet or a codon
what happens to make a polypeptide
to make a polypeptide, DNA is 1st copied into mRNA which s the 1st stage of protein synthesis
what is functional RNA
functional RNA is RNA molecules other than mRNA, which perform special tasks during protein synthesis e.g. tRNA and ribosomal RNA (rRNA)
in eukaryotes does all nuclear DNA code for polypeptides?
in eukaryotes, lots of the nuclear DNA doesn’t code for polypeptides
nuclear DNA = DNA stored in the nucleus
what are introns
genes that do code for polypeptides contain sections that don’t code for amino acids, these sections of DNA are called introns
what are intron’s purpose
there can be several introns within a gene and their purpose isn’t known for sure
what happens to introns in eukaryotic cells during protein synthesis
introns in eukaryotes are removed during protein synthesis so they don’t affect the amino acid order
do prokaryotic cells have introns
prokaryotic DNA don’t have introns
what are exons
all of the bits of a gene that do code for amino acids are called exons
what does eukaryotic DNA also contain?
eukaryotic DNA also contains regions of multiple repeats outside of genes . these are DNA sequences that repeat over and over. these areas don’t code for amino acids and are called non coding multiple repeats
what are alleles
a gene can exist in more than one form, these forms are called alleles
order of bases in alleles and what they code for
the order of bases in each allele is slightly different, so they code for slightly different versions of the same polypeptide
how many pairs of chromosomes do humans have
23 pairs of chromosomes, so 46 in total
what are homologous pairs
pairs of each matching chromosomes are called homologous pairs
similarities/differences in homologous pairs
in a homologous pair both chromosomes are the same size and have the same genes, although they could have different alleles
where will alleles coding for the same characteristic be found?
alleles coding for the same characteristic will be found a the same fixed position (locus) on each chromosome in a homologous pair
