Unit 4 - Genetic Info, Variation & Relationships b/w Organisms Flashcards
define gene
sequence of DNA bases that code for a polypeptide or for a functional RNA (inc. rRNA & tRNA)
define locus
fixed position on a chromosome that a gene occupies
define allele
different versions of a gene
different alleles have slightly different nucleotide sequences but occupy the same locus on the chromosome
how are chromosomes arranged?
homologous pairs
one inherited from the father & one inherited from the mother
eukaryotic DNA vs prokaryotic DNA
eukaryotic vs prokaryotic
linear (formed in chromosomes) vs circular
in nucleus vs in cytoplasm
no plasmids vs plasmids present
introns present vs no introns present
longer & more genes vs shorter & fewer genes
both are a double-stranded helix structure
how is DNA packaged in eukaryotes?
DNA double helix
DNA wraps around/associates with histones proteins
DNA-histone complex is coiled
coils fold to form loops
loops coil & pack together to form a chromosome (visible under light microscope)
what is the structure of a chromosome?
homologous chromosomes have same genes at the same specific loci but may have different alleles (paternal & maternal chromosomes)
duplicated chromosome - sister chromatids joined at the centromere
describe karyotype
picture of all the chromosomes from a single diploid cell
homologous pairs can be identified due to distinctive banding after staining
sex chromosomes displayed to one side
all other chromosomes are called autosomes
what sex chromosomes correspond to each gender?
xy - male
xx - female
define genome
complete set of genes in a cell
define proteome
full range of proteins that a cell can produce
or coded for by the cell’s DNA
what are the features of genetic code?
triplet code
degenerate
non-overlapping
universal
describe triplet code
a sequence of 3 bases (codon) codes for a specific amino acid
describe degenerate code
some amino acids are coded for by more than one codon
3 codons (stop codons) do not code for any amino acid & are used to mark the end of a polypeptide chain
the start of the sequence is always the same codon
describe non-overlapping code
each base in the sequence is only read once
code is always read in one direction along the DNA strand
describe universal code
DNA is the same in all organisms
same triplet code for same amino acids
why might mutations in nucleotide sequence of a gene not cause a change in structure of polypeptide?
triplets code for the same aa
mutation in introns/non-coding region
why might a mutation have no effect on an individual?
mutation in intron
new allele is recessive so does not affect phenotype
why might a mutation have a positive effect on an individual?
increase survival chance
increase reproductive success
describe messenger RNA
function: transfers DNA code from nucleus to cytoplasm & determines the sequence of aas during protein synthesis
complementary to DNA code
small enough to leave nucleus via nuclear pores
associates with ribosomes in cytoplasm
easily broken down & only exists when needed to make a protein
sequence of nucleotides in mRNA = genetic code
describe the process of transcription
DNA helicase separates polynucleotides by breaking hydrogen bonds (b/w DNA bases)
the non-coding DNA strand acts as a template
free RNA nucleotides align by complementary base pairing
uracil base pairs with the adenine on DNA instead of thymine
RNA polymerase joins adjacent RNA nucleotides
phosphodiester bonds, needing ATP
in eukaryotes, pre-mRNA is spliced & introns removed to form mRNA
describe the process of splicing
introns (non-coding sections) are removed
remaining exons (coding sections) join together
splicing does not happen in prokaryotes
compare DNA replication & transcription
replication uses DNA polymerase to synthesise new DNA polynucleotides vs transcription uses RNA polymerase to synthesise new RNA polynucleotides
replication creates identical DNA molecules before cell division by mitosis vs transcription converts DNA into mRNA
describe tRNA
small, single-stranded molecule
clover shape with one end of the chain longer
the longer section is the amino acid binding site, which binds to a specific aa
each tRNA carries a different aa to the ribosome
each tRNA has a specific anticodon, which pairs with the complementary codon on the mRNA by H bonds