Genetic information, variation and relationships between organisms Flashcards
what is DNA?
deoxyribose nucleic acid
what bonds hold together nitrogenous bases?
hydrogen bonds
what bonds hold together the nucleotides?
phosphodiester bonds
Eukaryotic DNA vs Prokaryotic DNA
Eukaryotic larger/longer associated with proteins (histomes) found in linear chromosomes contained within the nucleus
Prokaryotic shorter no protein not in chromosomes not in a nucleus
what are chromosomes
23 pairs
maternal and paternal chromosomes
diploid if 23 pairs except gametes (sex cells as 23 in each)
what are homologous chromosomes
two chromosomes that are the same by structure but they are not genetically identical
what is a gene
a section of DNA that codes for a polypeptide or functional RNA
what is an allele
a version of a gene
what is the locus
position of an allele, same on maternal and paternal gene
what does homologous mean
the same structure but not genetically identical
MRNA vs DNA
MRNA single strand of DNA AUCG bases polymer ribose sugar short molecule
DNA double helix structure ATCG bases polymer deoxyribose sugar long molecule
what is transcription
the formation of MRNA in the nucleus
what is translation
the formation of a polypeptide chain (a protein)
how does DNA replicate
hydrogen bonds break by DNA helicase enzyme
free nucleotides complementary base pair with the template strand
RNA/DNA polymerase re-synthesizes the sugar phosphate back bone and forms phosphodiester bonds
what does DNA helicase do
breaks hydrogen bonds and unzips double helix structure into a single strand
what does RNA/DNA polymerase do
re-synthesizes the phosphate back bone and forms phosphodiester bonds
what is a template strand
the strand which is being read
what happens in transcription
- DNA helicase breaks the hydrogen bonds into single strands and forms pre MRNA
- RNA nucleotides complementary base pair
- RNA polymerase re-synthesizes the suger phosphate backbone forming phosphodiester bonds
- Non-coding DNA is removed (exons removed)(splicing)
- MRNA then goes to the ribosomes
what does MRNA and pre MRNA contain
MRNA - coding DNA (introns)
pre MRNA - non coding and coding DNA (introns and exons)
what does universal mean
all triplet codes can code for the same amino acid
what does degenerate mean
triplet codes can code for more than one amino acid
what happens in translation
- MRNA attaches to ribosome
- ribosomes move to start codon
- TRNA brings specific amino acid
- anti-codon on TRNA is complementary to codon on MRNA
- ribosome moves along to the next codon
- ribosome fits around two codons
- condensation reaction occurs
- process repeated and amino acids joined by peptide bonds
how is TRNA adapted to suit its role
- transports specific amino acids
- 20 different TRNA’s (degenerate)
- all share the same structure
three types of mutation
- insertion
- deletion
- substitution
what is a mutation
a change in one or more nucleotide base or a change in the sequence of the bases in DNA
what is a mutagen
a physical or chemical agent that changes the genetic material of an organism
factors that act as mutagenic agents
UV radiation
X-rays
caffeine
mustard gas
what is a chromosomal mutation
changes in the number or structure of whole chromosomes
two main types of chromosomal mutation
polyploidy
non-disjunction
what happens in polyploidy
many copies
changes in whole sets of chromosomes
cells have multiple sets of chromosomes
3n triploid which is common in plants
what happens in non-disjunction
not seperated equally
homologous pairs fail to separate
chromosome in 21, 3 in one side 1 in the other and this 1 is then destroyed
e.g downs syndrome
meiosis vs mitosis
mitosis growth and repair 1 division 2 daughter cells 46 chromosomes, 23 pairs same genes (identical)
meiosis
a diploid nucleus divides to produce 4 haploid daughter cells
2 divisions
4 daughter cells
23 chromosomes in each
similar to parental cells but not identical
2 main forms of genetic variation
crossing over
independent segregation
what happens during crossing over
parts of chromosomes swap round
exchange of the alleles
what happens during independent segregation
random arrangement of the chromosomes
what is a genotype
the genetic makeup of an organism and the genes and alleles that they have
what is a phenotype
observable characteristics - genotype + environment = phenotype
causes of genetic variation
mutations
sexual reproduction
meiosis ( crossing over and independent segregation )
