DNA & Genetic Diversity Flashcards
What does DNA stand for?
Deoxyribonucleic acid
What does RNA stand for?
Ribonucleic acid
What does DNA do?
hold genetic info
What does RNA do?
transfer genetic information from DNA to ribosomes
What is DNA and RNA polymers of?
Nucleotides
What is the structure of DNA?
two polynucleotide strands
joined by hydrogen bonding
forming a double helix
What is in a DNA nucleotide?
pentose sugar> deoxyribose
phosphate group
nitrogen containing bases
What are the bases in DNA?
Adenine
Thymine
Guanine
Cytosine
What bonds join nucleotide together?
phosphodiester bonds
formed by condensation reactions
What bond joines bases together?
hydrogen bonds
(Maintain stable structure due to its abundance)
Describe the process of semi-conservative DNA replication
- DNA helicase breaks hydrogen bonds & separates the two polynucleotide strands
- strands act as a template
- free nucleotides attach to complementary bases
- DNA polymerase join the strands of the nucleotides
- two new identical DNA strands (new and old)
What are the differences between DNA and RNA
pentose is Ribose in RNA
Uracin instead of Thymine
mRNA and tRNS are single strands
What are the properties of mRNA?
has linear structure
codons(base triplets)
involved in protein synthesis
Describe the shape of tRNA
clover leaf shape due to hydrogen bonds between complementary bases
Describe the properties of tRNA
anticodon ( 3 unattached tRNA nucleotide bases) on one end
binding site for amino acids on the other end
How is a chromosome formed?
from DNA and its associated protein
What is the shape of DNA in the nucleus of eukaryotic cells?
long and linear
What is the shape of DNA in mitochondria and chloroplasts?
short and circular
What are Chromosomes?
2 sister chromatids joined together by a centromere
product of DNA replication
formed from histones and DNA during cellular division
What is a gene?
A section of DNA base that code for specific amino acid sequence
What are diploid cells?
Have chromosomes in pairs, one inherited from one parent and one from the other
what is a homologous pair of chromosome?
two chromosomes that carry the same genes but not the same alleles
maternal and paternal chromosome
What is a locus?
Fix position of a gene on a particular DNA molecule or chromosome
what is a base triplet?
A sequence of three nucleotide bases the code for a specific amino acid
what are codons?
based triplets in mRNA that code for an amino acid
what is it meant by degenerate?
One amino acid can be coded for by different triplets
what are stop codes?
They do not code for an amino acid, but they indicate the end of a code for specific polypeptide
How are codes none overlapping?
each base is only read once as part of a specific triplet
How are codes universal?
The same triplets code for the same amino acid in all organisms
What is an Intron?
Base sequences present in genes, but don’t code for amino acids
what is an Exon?
base sequences in genes that code for amino acids
What are multiple repeats?
some of the base sequences present between genes
it consists of the same sequence occurring again and again
What are some examples of non-coding DNA?
intron
Multiple repeats
What is a genome?
complete set of genes in a cell
what is a proteome?
The full range of proteins that are cell is able to produce
What is transcription?
occurs in the nucleus
involves rewriting part of the DNA into a strand of messenger RNA
Outline transcription
- The relevant DNA uncoils and strand separate
- One of these strands act as a template
- Individual RNA nucleotides lineup along the complementary DNA base
- individual RNA is joined together by RNA polymerase
- The two strands of DNA will join back together once mRNA has been produced
what is pre-mRNA?
mRNA formed during transcription
What is splicing?
removing introns from pre-mRNA and joining together exons to form mRNA
Why does splicing not happen in prokaryotes?
prokaryotes DNA does not contain introns
What happens during translation?
happenes in ribosomes
sequence of codons on the mRNA strand is used to determine the sequence of amino acids in the polypeptide
What is genetic diversity?
The number of different alleles in a population
What causes genetic diversity?
- gene & chromosome mutations
- meiosos
- random fusion of gametes during fertilisation
What is gene mutation?
changes in the sequence of nucleotide bases
new alleles of genes are produced
What are mutagenic agents?
increase the rate of mutation
(x-rays, benzene)
What are the different types of mutations?
substitution
addition
Deletion
Duplication
Inversion
Translocation
What is substitution?
the replacement of one or more bases by a one or more different base
What does substitution result in?
- a new triplet coding for a different amino acid, this may result in a non functional protein
- one different amino acid changes but a functional protein is still produced
- same amino acid may be coded for due to degeneracy, so polypeptide remains unchanged
What is deletion?
removal of one or more bases
resulting in frame shift
What is a frame shift?
alteration in all triplets from the point of mutation
the protein formed is nearly always non functional
What is addition?
addind one or more bases
results in frame shift
What is duplication?
when one or more bases are repeated
results in frame shift
What is inversion?
where a sequence of bases is reversed
What is translocation(mutation)?
where a sequence of bases is moved from one location to another
What is an allele?
different forms of genes that code for different types of the same characteristic
arise due to mutations of a gene
What is mitosis?
produces cells that are genetically identical
two daughter cells
What are the stages of mitosis?
Prophase
Metaphase
Anaphase
Telophase
What happens during interphase?
cell prepares for nuclear division
- DNA is doubled
- Increase in protein synthesis
- cell organelles are replicated
What happenes in prophase?
each chromosome shortens then thickens(condensation)
nuclear membrane breaks down
What happens during metaphase?
centrioles from a spindle across the cell, this spindle consist of protein microtubules
Each chromosome moves to the equator of the spindle and attaches to it by its centromere
What happens during anaphase?
The centromere splits and sister chromatids separate
sister chromatids are pulled to opposite poles of the cell by the spindle microtubules
what happens during telophase?
chromatids are at opposite poles and begin to uncoil
Nuclear membrane reforms
The two cells or genetically identical to each other and the original parent cell
What happens during Cytokinesis?
The cytoplasm splits in two
Two new cells form as the cell surface membrane (plant cell: cell wall) forms
What is cancer?
A group of diseases caused by uncontrolled growth and rapid cell division
Results from damage to genes that regulate mitosis s and cell cycle
What is a tumour?
A group of abnormal cells
how do drugs help with cancer?
They can inhibit the enzymes, (DNA helicase or DNA polymerase) or inhibit the formation of the spindle
What is meiosis?
nuclear division that produces cells that are genetically different
four non identical daughter cells
What type of gametes are produced during meiosis?
Haploid
diploid number will be restored at fertilisation
What happenes during meiosis?
two nuclear divisions
What happens during late interphase in meiosis?
DNA replication
Buildup of ATP
Protein synthesis and replication of organelles
what happens in meiosis I?
The first division separates the membranes of each homologous pair
what happens in meiosis II?
Chromatids are separated from each chromosome
What is independent segregation of homologous chromosomes?
In meiosis, chromosomes pair then separate so one from each pair enters the gamete
how do you calculate the possible number of varied combinations?
2^n
n= number of pairs
What is crossing over?
The two members of each homologous pair lie side-by-side forming a bivalent
The chromatids of the homologous chromosomes then interwine
What is the name of the place where crossing over occurs?
Chiasma
What does does crossing over lead to?
exchange of alleles of the same gene
this can produce new combinations of alleles called recombinants
Why is the number of recombinants low?
beacuse crossing over is rare
What is chromosome non-disjunction?
when a homologous pair of chromosomes do not separate on the first meiotic division
both members of a homologous pair o to the same side during anaphase I
What is the result of chromosome non-disjunction?
gametes will have one extra/less chromosome than normal
What is genetic diversity?
the number of different alleles of genes in a population
How do new alleles come about?
random mutations
What is directional selection?
when there is a change in the environment in which the alleles of an extreme type are selected for
What is stabilising selection?
(nothings changing)
an average phenotype is selected for and extremes of the phenotype are selected against
