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As bio 3.4.1 dna. genes. and chromosomes.
Terms in this set (80)
What are DNA molecules like in prokaryotic cells?
Short, circular, and not associated with proteins
What are DNA molecules like in the nucleus of eukaryotic cells?
Very long, linear and associated with proteins, called histones.
What does a dna molecule and it's associated proteins form?
Where else in a eukaryotic cell, apart from the nucleus can dna molecules be found?
Mitochondria and chloroplasts.
What are dna molecules like in the mitochondria and chloroplasts of or eukaryotic cells?
Short, circular and not associated with protein, like in prokaryotic cells.
What is a gene?
A Base sequence of dna that codes for: 1. The amino acid sequence of a polypeptide 2. A functional RNA (including ribosomal RNA and tRNAs)
What two things do genes code for?
1. The amino acid sequence of a polypeptide 2. A functional RNA (including ribosomal RNA and tRNAs)
Where are genes found?
A fixed position, called a locus on a particular DNA molecule.
What is a locus
The fixed position of a gene on a particular DNA molecule.
What codes for an amino acid?
A sequence of 3 DNA bases, called a triplet or codon
What are histones?
Circular Proteins that the dna molecule is coiled around so it can fit into the nucleus of a eukaryotic cell
Why are histones helpful
The provide support for the DNA molecule as well as allowing it to coil up smaller.
How do the DNA molecules in prokaryotic cells condense to fit inside prokaryotic cells?
It condenses by supercoiling (coiling/scrunching up really small)
What is functional RNA?
RNA molecules other than mRNA which perform specific tasks related to photosynthesis. E.g. rRNA which forms part of ribosomes
What Is a cell's genome?
The complete set of genes in a cell
What is a cell's proteome?
The full range of proteins that the cells is able to produce.
What are introns?
Sections of genes that don't code for amino acids
What is the purpose of introns?
Why don't introns in eukaryotes affect the amino acid order?
They are removed during protein synthesis.
Does prokayotic DNA have introns?
What are exons?
All of the bits of a gene that do code for amino acids
What is an allele?
Different forms of a gene that code for slightly different versions of the same polypeptide e.g. eye colour.
What is mRNA?
Messenger RNA, it carries the genetic code from the DNA (in the nucleus) to the ribosome where it's used to make a protein during translation
When is mRNA made?
What is the structure of mRNA?
A single polynucleotide strand, groups of 3 adjacent bases in mRNA are called codons.
What is tRNA
Transfer RNA, it's involved in translation, it carries the amino acids that are used to make proteins to the ribosomes.
What is the structure of tRNA
A single polynucleotide strand that is folded into a 3 leaved clover shape.
What holds tRNA molecules in their clover shape?
Hydrogen bonds between specific Base pairs
What is an anti codon ?
The specific sequence of 3 bases at one end of a tRNA molecule.
What is at the opposite end of a tRNA molecule to its anticodon?
It's amino acid binding site.
What is transcription?
The production of mRNA from DNA
What is the role of RNA polymerase?
Joining mRNA nucleotides
What happens during transcription?
An mRNA copy of a gene
Is made from DNA.
Where does transcription take place in Eukaryotic cells
In the nucleus
Where does transcription take place in prokaryotic cells?
In the cytoplasm (because they don't have a nucleus)
What are the stages of transcription?
1. RNA polymerase attatches to the DNA
2. Complementary RNA is formed.
3. RNA polymerase moves down the DNA strand
4. RNA polymerase reaches stop signal
What happens during the 1st stage of transcription
RNA polymerase attatches to the DNA double-helix at the beginning of a gene. The hydrogen bonds between the two DNA strands in the gene break, separating the strands, and the DNA molecule uncoils at that point, exposing some of the bases. One of the strands is then used as a template to make an mRNA copy
What happens in the 2nd stage of transcription?
The RNA polymerase lines up free RNA nucleotides alongside the exposed bases on the template strand. The free bases are attracted to the exposed bases. Specific, complimentary Base pairing means that the mRNA ends up being a complimentary copy of the DNA template strand once the RNA nucleotides have paired up with their specific bases on the DNA strand, they're joined together RNA polymerase, forming an mRNA molecule.
What happens in the 3rd stage of transcription?
The RNA polymerase moves along the DNA, separating the strands and assembling the mRNA strand. The hydrogen bonds between uncoiled strands of DNA re-form once the RNA polymerase has passed by and the strands coil back into a double helix.
What happens during the 4th stage of transcription?
When RNA polymerase reaches a particular sequence of DNA called a stop signal, it stops making mRNA and detaches from the DNA.
What's the difference between transcription in eukaryotes and prokaryotes?
In eukaryotes the introns and exons are both copied into mRNA during transcription, creating pre-mRNA, then splicing occurs and the introns are removed and the exons joined together. In prokaryotes mRNA is produced directly from the DNA without splicing taking place, there are no introns in prokaryotic DNA.
What is translation?
The second stage of protein synthesis, the production of polypeptides from the sequence of codons carried by mRNA.
What is the role of ribosomes in translation?
The mRNA attatches itself to a ribosome and tRNA molecules carry amino acids to it. When the amino acids are lined up in the correct order, the ribosome joins them together.
What is the role of tRNA in translation?
tRNA molecules carry amino acids to the mRNA and attach themselves to the mRNA by complimentary Base pairing. Then a second tRNA attatches itself to the next codon and so on.
What is the role of ATP in translation?
It provides the energy needed for the bond between the amino acids and the tRNA molecules to form.
What is a gene mutation?
A change in the Base sequence of chromosomes .
How does a mutation occur?
Spontaneously during DNA replication and include Base deletion and Base substitution .
Why do not all base substitutions cause a change in the sequence of encoded amino acids.
Because the genetic code is degenerate. (there are many instances in which different codons specify the same amino acid.)
What things increase the the rate of gene mutation?
How do mutations in the number of chromosomes happen?
Spontaneously by chromosome non-disjunction during meiosis.
What is meiosis?
Cell division that takes place in the reproductive organs of multicellular eukaryotic organisms. The production of 4 haploid daughter cells from a diploid parent cell.
Why are the daughter cells from meiosis genetically different?
Independant segregation of homologous chromosomes.
What causes further genetic variation among daughter cells in meiosis?
What is crossing over?
During meiosis 1 homologous chromosomes come together and pair up, the chromatids twist around eachother and bits of chromatids swap over. They now have a different combination of alleles.
What is genetic diversity?
The number of different alleles of a gene in a population
What are the stages/principles of natural selection
● random mutation results in new alleles of a gene
● in certain environments the new allele of a gene may benefit it's possessor leading to increased reproductive success
● the advantageous allele is inherited by members of the next generation
● as a result over many generations the new allele increases in frequency in the population.
What is directional selection?
When individuals with alleles for characteristics of an extreme type are more likely to survive and reproduce, could be in response to an environmental change.
What is a good example of directional selection?
Bacteria evolving antibiotic resistance.
What is stabilising selection?
When individuals with alleles for characteristics towards the middle of the range are more likely to survive and reproduce. Occurs when the environment isn't changing and reduces the range of possible characteristics
What is an example of stabilising selection
Human birth weights
What determines if two organisms belong to the same species?
If they are able to produce fertile offspring
What is courtship behaviour?
Behaviour carried out by organisms to attract a mate of the right species.
How can courtship behaviour be used in species recognition?
It is species specific, only members of the same species will do and respond to that courtship behaviour.
Why is it important for courtship behaviour to be species specific?
To prevent interbreeding and making reproduction more successful.
What are examples of simple courtship behaviours?
● releasing a chemical e.g. male bumblebees release pheromones to attract females
● using sound e.g. male red deers roaring
● visual displays e.g. great tit puffing out it's chest
What are examples of complex courtship behaviours?
● Dancing e.g. blue-footed boobies
● building e.g. bower birds construct bowers (shelters out of leaves and twigs etc.
What is a phylogenetic classification system
One that arranges species into groups based on their evolutionary origins and relationships.
What is the hierarchy of organism classification?
Domain, Kingdom, phylum, class, order, family, genus, species.
How does the binomial system work?
Each species is universally identified by a binomial consisting of the name of it's genus and species e.g. homo sapiens.
What different techniques are there of investigating diversity?
● comparing characteristic of organisms
● comparing DNA base sequences
How does comparison of DNA base sequences to investigate diversity work?
Each nucleotide is tagged with different coloured dye producing a series of coloured bands each of which representing 1 of the 4 nucleotide bases. Comparing these patterns you can see how similar and more closely related organisms are based on their DNA base sequences.
What is biodiversity?
The variety of different organisms in an area
What is a habitat?
The place where an organism lives
What is a community?
All the populations of different species in a habitat.
What is species richness?
A measure of the number of different species a community
What is an index of diversity?
An index describing the relationship between the number of species in a community and the number of individuals in each species.
How do you calculate an index of diversity?
D= N(N-1)/∑n(n-1) where N=total number of organisms of all species and n= total number of organisms of each species.
How does farming affect biodiversity?
It reduces it
Why does farming reduce biodiversity?
Clearing directly removes species, destroy habitat and food, pesticides kill organisms, herbicides as well
Whay different ways can genetic diversity within, or between species Be observed?
● frequency of measurable or observable characteristics
● the Base sequence of mRNA
● the Base sequence of DNA
● The amino acid sequence of the proteins encoded by DNA and mRNA
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