3.4.1 DNA, genes and chromosomes Flashcards
what is a gene?
section of DNA that contains the coded information for making polypeptides and functional RNA
coded information is in the form of a specific sequence of bases along the DNA molecule
genes determine the proteins of an organism
A GENE IS ON A SECTION OF DNA LOCATED AT A PARTICULAR POSITION CALLED A LOCUS ON A DNA MOLECULE
codes for:
the amino acid sequence of a polypeptide
functional RNA
what is the genetic code?
rule that a minimum of three bases code for each amino acid
only 20 different amino acids in proteins
each amino acid must have its own code of bases on DNA
4 different types of bases A,G,C,T
64 possible triplet codes and 20 amino acids
more then one triplet code codes for the same amino acid = degenerate
what are the features of the genetic code?
degenerate
code is non-overlapping = base in each sequence is read once
code is universal = triplet codes code for the same amino acid in each organisms
what are introns and exons?
exons = non-coding sequences made up of multiple repeats of base sequences
introns = exons are separated by further non-coding sequences called introns
what’s the DNA difference between prokaryotes and eukaryotes?
prokaryote:
- DNA is smaller
- forms a ring
- not associated with histone proteins
- do not have linear chromosomes
eukaryote:
- DNA is larger
- forms a line (linear)
- associated with histone proteins
- forms chromosomes
why do mitochondria and chloroplasts have DNA too?
strong evidence points to endosymbiosis = specific type of symbiosis where one organism lives inside another
symbiosis = relationship in which organisms from two separate species live in a close dependant relationship
through millions of years of evolution, aerobic bacteria become chloroplasts
what is a chromosomes structure?
chromosomes appear as two threads, called chromatids that are held together by a central point called the centromere
chromatids are generally identical copies of one another
DNA is wound around histone proteins to fix it in position, then further coiled to form a chromosome
homologous pairs
how many chromosomes are in humans?
full number of chromosomes is called the diploid number (46 in humans)
when gametes are formed by meiosis, each daughter cell receives one chromosome from each pair
number of chromosomes are halved = haploid (23 in humans)
what are homologous pairs?
always two chromosomes that carry genes that determine the same genetic characteristics at the same position (locus)
both chromosomes in the homologous pair carry the gene for eye colour
alternative forms = alleles
what is an allele?
one of a number of alternative forms of a gene
transfer RNA
Collects amino acids and take them to the ribosomes forassembly into proteins
small molecule = around 80 nucleotides
Wind back onto itself to form a clover leaf shape
One end carries amino acid
One loop as a special triplet of bases which determines the amino acid carried
what is Messenger RNA?
manufactured in the nucleus from one strand of the DNA double helix
The sequence of a
nucleotide bases on mRNA is the genetic code
Condon = three bases on mRNA that codes for a single amino acid
Base sequence of mRNA is complementary to template strand of DNA
What is formed the mRNA passes out into the cytoplasm and attaches itself to the ribosome where proteins are synthesised
Variable in length and base sequence
how is coded information transferred?
DNA code are transcribed onto a single-stranded molecule (RNA)
genome = the complete set of genes in a cell, including those in mitochondria and chloroplasts
proteome = full range of proteins produced by the genome
