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218 Cards in this Set
- Front
- Back
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What is the dna like in prokaryotic cells? |
Short and circular and not associated with any proteins(histones) so does not form chromosomes |
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What is the dna like in eukaryotic cells? |
Found in the nucleus , long , linear and associated with proteins called histones to form chromosomes |
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Where else can you find dna in a eukaryotic cell? |
Mitochondria and chloroplast |
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What is the dna like in these organelles? |
Like prokaryotic dna |
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How is dna wrapped up into chromosomes? Why is this helpful |
The dna histone complexes coil up and then the coils loop and it all folds up into a chromosome Helpful as dna is super long |
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What is a gene? What can it code for? |
A section of dna which is a base sequences that codes for amino acid sequences in polypeptide chains and can also code for functional RNA such as RNA that makes up ribosomes and tRNA involved in proteinsynthesis |
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How many bases code for one amino acid? |
3 (a triplet) |
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How is the code read? |
In one direction and non overlapping and as triplets , each base is only read once |
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What is the fixed position a gene occupys called? |
A locus |
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What does degenerate mean? |
More than one triplet can code for the same amino acid |
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How many triplets can code for one amino acid? |
Normally between 2 and 6 |
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What is the purpose of this? |
To provide protection from mutations - base sub of one triplet occurs but new triplet still codes for same amino acid as is degenerate |
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How many possible triplets exist? |
64 |
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How many amino acids exist? |
20 |
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Some triplets code for something else other than an amino acid , what? |
Stop codes which mark the end of a polypeptide chain |
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What are introns? |
Codes that do not code for anything - does not code for protein or functional RNA |
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What are exons |
Codes that code for something , proteins and functional RNA |
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How many chromosomes do humans have? |
46 (different for different species but is always an even number so meiosis can occur) |
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What are alleles? |
Different forms of the same gene (slightly different base sequence so new ones can be produced by DNA mutations) |
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They can be... |
Dominant or recessive |
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What does diploid mean? |
Full chromosomes e.g body cells |
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What does haploid mean? |
Half chormosomes e.g gametes |
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What are homologous chromosomes? |
Pair of chromosomes with same genes in the same positions but different alleles - determine characteristics( only have 23 different chromosomes but 2 of each one from mother and father makes 46) |
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What is a genome? |
All genes present in a cell - complete set , including the ones in the mitochondria and chloroplasts |
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What is a preteome? |
The full range of proteins that a cell is able to produce from its genome |
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What are RNA nucleotides made up of? |
Ribose sugar , phosphate group and the bases guanine cytosine , adenine and uracil |
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General characteristics of mRNA? |
Long (shorter than DNA but longer than tRNA) , single-stranded , most unstable , smaller than DNA but bigger than tRNA , quantities in cells vary depending on expression of certain genes due to specialisation |
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General characteristics of tRNA? |
Smallest, single-stranded clover shape which is more stable than mRNA but less than DNA Quantities vary Chain extends beyond the other so can attachment to specific amino acid Has anticodons on other side One for every triplet exists |
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Whats a codon? |
3 base sequences on mRNA which code for one amino acid |
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Whats an anticodon? |
Three bases on a tRNA molecule |
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What is the codon complementary to? |
The anti codon |
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What anticodons complementary to? |
Codons and specific amino acids |
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What does the overall process of transcription result in? |
mRNA is produced from DNA |
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Where does transcription take place? |
In the nucleus |
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What does DNA helicase do? |
Unwinds the double helix of DNA and breaks the hydrogen bonds between the complementary bases |
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What is the job of the exposed DNA bases? |
Acts as a template to build pre-mRNA (only one of the exposed strands) |
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How is pre-mRNA formed? |
Free RNA nucleotides are attracted and form hydrogen bonds with the complementary exposed base pairs and RNA polymerase joins all these nucleotides together to form phosphodiester bonds |
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When does complementary base pairing stop? |
When a stop code is reached (terminator region?) |
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How is mRNA formed from pre-mRNA? |
Pre-mRNA undergos splicing in which rna coded from introns are removed and rna coded from exons are bonded together to from mRNA |
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Why is there no need for splicing in prokaryotic cells? |
mRNA is produced directly from the transcription of DNA (just exons and no introns) |
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What is the overall purpose of translation? |
The production of polypeptides from the codons on mRNA |
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Where does translation take place? |
The ribosomes in the cytoplasm |
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How do mRNA molecules move into the cytoplasm from the nucleus? |
Via the nuclear pores - can do this as they're small |
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Where do the ribosomes attatch to mRNA at? |
The starting codon |
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How many codons can a ribosome hold at one time? |
2 |
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What attatches to the codons? |
Complementary tRNA molecules with a complementary anticodon that carry the specific amino acid |
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What do the ribosomes do? |
Break the bond between tRNA and the amino acid and form a peptide bond with the amino acid ajacent using an enzyme and energy from the hydrolysis of ATP ( translation is active!!!) - they do this as they move along |
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How many codons do the ribosomes shift along after forming a peptide bond? |
One codon |
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What do the tRNA molecules which detatch from the amino acid do? |
Attatch to another amino acid specific to the anticodonso they can be used again |
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What is a mutation? |
A sudden change is amount or arrangement of genetic material |
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More specifically ,what is a gene mutation? |
Change in base which changes the base sequence on dna |
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What does a change in base sequence result in? |
Change in amino acid sequence (not always as DNA is degenerate) |
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What can a change in amino acid sequence lead to? |
A non-functional protein being formed |
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Why? |
The bonds are changed so the tertiary structure is changed(due to primary structure change) which will change the overall shape of the protein effecting its function |
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Where do mutations occur? |
Dna replication |
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What is a base substitution mutation? |
A base on the dna strand is replaced with a different base which changes one of the triplets on the dna molecule. |
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What are the two possible outcomes of this? |
A different amino acid is coded for so the polypeptide chain is changed ( significcance depends on importance of the original amino acid in the tertiary sturcture , is it part of the active site of an enzyme?) or it can have no effect |
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Why can substitution have no effect? |
Dna is degenerate - new triplet may still code for the same amino acid |
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What is a deletion/addition mutation? |
A base is added or removed which changes every single triplet after this mutations and causes the reading frame to change (frameshift)- deletion to the left , addition to the right |
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Why is base deletion/addition more serious? |
The polypeptide coded for is completely different due to many triplets changing. Therefore a non-functional protein is formed |
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What do mutagenic agents do? |
Increase the rate at which mutations occur |
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What is a chromosome mutation? |
A change in the structure or number of whole chromosomes |
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What is a change in whole sets? |
Having more than two sets of chromosomes |
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What is the word for this? |
Polyploidy |
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What is a change in the individual number? |
Homologous chromosomes fail to seperate in meiosis 1 which results in gametes with incorrect numbers of chromosomes (extra of a certain chromosome when you should only have 2 or less than 2) |
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What is the word for this? |
Non-disjunction |
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How can proteinsynthesis be reduced but not stopped? |
Have two mRNA molecules which are complementary to eachother so they will bind and form a double strand so they cannot be read by the ribosomes and polypeptides cannot be formed. |
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How many nuclear divisions are involved in meiosis? |
Two |
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What does this result in the formation or? |
4 non identical gametes which are haploids |
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Two reasons why meiosis is important? |
Allows genetic variety within a species (which is important for adaptations and survival) as produces different allele combos in gametes which fuse with random other combos producing individuals with many different allele combos (asexual reproduction produces identical offspring- not variety) and keeps the number of chromosomes constant throughout generations due to the halfing and doubling at fusion |
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What is the first part of meiosis? (Interphase) |
Dna replicates |
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Then what ? (Metaphase) |
Homologous chromosomes line up next to eachother (bivalents form) at the equator in a random order called random assortment(leads to independent segregation) |
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What does random assortment provide? |
Genetic variation - random mixture of maternal and paternal alleles in each gamete |
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What do the chromosomes do lined up next to eachother? |
Maternal and paternal chromosomes exchanged genetic material such as alleles in a process known as crossing over where chromatids wrap around eachother forming chiasmata and equal sections snap off and rejoin on other chromosome (recombination) |
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When the chromosomes seperate in anaphase this is known as? |
Independent segregation of homologous chromosomes |
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What happens in the second division? |
Chromosomes split at centromere and spindle fibres pull chromatids to poles to form gametes |
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How do you work out how many variation of a gamete there is from one organism? (Not taking crossing over into account - only all the different combos from independent segregation) |
2^n . n= number of pairs of chromosomes |
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How do you work out variety of individuals after fusion of the gametes? |
(2^n)^2 n= number of pairs of homologous chromosomes |
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Exchanging alleles results in.. |
Recombination of genetic material |
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What are some examples of mutagenic agents? |
High energy ionising radiation , benzene-chemicals , tar from cigs , viruses, UV light |
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Describe and explain the appearance of chromosomes. |
Two identical sister chromatids joined at centromere as a result of DNA replication in interphase |
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Is crossing ovee frequent? |
No its quite rare |
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Same species have the same... |
Genes (species can breed together to produce fertile offspring as diploid number will be even) |
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But differ in... |
Alleles (have different DNA)- creates variety and different looking individuals within the species |
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What is genetic diversity? |
The total number of different alleles of genes in a population( greater number of different alleles = more variation in the species as individuals have different characteristics) |
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What is a population? |
A group of individuals of the same specues that live in the same place and can interbreed |
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What does genetic diversity allow? |
Natural selection |
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Why? |
Variation means that it is more likely a certain allele which causes a characteristic will be suited to the selection pressure /environment so those individuals survive and the population adapts overtime instead of them all dying out because they're not suited to the environment |
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What makes a species more likely to survive an environmental change |
High genetic diversity |
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Individuals who have beneficial alleles... |
Are at an advantage and will survive to pass on alleles to their offspring (have greater reproductive success) , after many generations this eventually results in evolution as alleic frequency continues to increase |
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What can random mutations create ? |
New alleles of a gene which leads to a new characteristic |
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Which may be? |
Beneficial to the possesor ( better suited to selection pressures more likely to get resources at the expense of others - outcompete) |
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What increases from natural selection? |
Alleic frequency of this advantageous allele increases within a population |
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What are selection pressures? |
Something that causes a species to change (like an environment change as favours different alleles so alleic frequencies change due to differential survival ) |
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Which type of selection involves a sudden environmental change? |
Directional (favours individuals that vary in a certain direction from the mean) - changes the characteristics of the population over time as the mean changes |
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Therefore no environmental change favours... |
The mean as same selection pressures remain , favouring the already mean and selecting against extreme phenotypes |
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This preserves... |
The populations characteristics |
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And decreases.. |
The extreme phenotypes |
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How does the normal distribution change? |
Gets thinner and taller as more individuals with average alleles and less with extremes |
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The selective pressures exist for... |
The extreme phenotypes as mean is best suited to current environment - they are not so are selected against |
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Ehat does environment change create? |
Selection pressures |
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Therefore what happens to the curve? |
Shifts to get a new mean |
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Why? |
Extreme phenotypes are favoured as new selection pressure , old mean no longer favoured due to this change, so their population increases as they have better survival and reproductive success and after many generations they become the new mean as alleic frequency continues to increase |
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What is an example of directional selection? |
Antibiotic resistant bacteria - random mutation caused bacteria to be resistant - produced protein which prevented antibiotic from killing the bacteria so had a greater survival rate than others increasing in number so alleic frequency for resistance increases - new mean. (Use of antibiotics = selection pressure) |
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Example of stabilising selection? |
Birth weights of babies - extremely underweight or overweight have high infant mortality so surivival reduced. Mean survives and passes on alleles to produce more mean weight babies increasing the frequency. Extremes die so cant pass on and their frequency reduces |
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How are antibiotic resistant bacteria stopped? |
Use less antibiotics so they wont be at an advantage for being resistant as selection pressure isnt present they dont have an advantage over other bacteria so numbers dont get as large |
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Are mutations brought on by anything? |
No they are randomly occuring in dna replication |
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What is anatomical selection? |
Changing body parts so more suited to environment |
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Physiological selection? |
Changing inside processes so better suited to environment |
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Behavioural selection? |
Changing the behaviour of a species for better chance of survival |
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What is classification? |
The organisation of living organisms into groups- as so many different species exist |
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What is significant about individuals of the same species? |
They can interbreed to produce living fertile offspring |
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In the past how were organisms classified? |
Depending on physical features- need something that can be used universally and so every organism has its own name - prevents confusion |
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Now we use a universal naming system called... |
The binomial system(which simply means they are identified via 2 names) |
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What two taxa make up an organisms name |
Genus-species |
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Which one has a capital letter? |
The genus |
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Other words for these names are... |
The generic and the specific name |
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What is a rule about the specific name? |
It is never shared with another species |
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What do we write if the specific name is unknown? |
Sp |
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Taxonomy is... |
The theory and practice of biological classification |
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What is artifical classification |
Grouping organims based on physical features and function , does not include evolutionary origin as similar features may not be linked by evolution |
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What is phylogenetic classification? |
Based on evolutionary relationships between present organisms and ancestors which are extinct ,similar features come from common ancestors (homologous characteristics) and involves the use of a hierachy containing taxa to split organisms up into groups |
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What is a problem with artificial classification? |
Its subjective - causes confusion and isnt universal |
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Define hierachy |
Smaller grous within larger groups that do not overlap ( bacteria archaea eukarya in domain) |
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What is each group in the binomial system referred to? |
Taxon |
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Plural is? |
Taxa |
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What is the order of the taxa when naming? |
Domain kingdom phylum class order family genus species |
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What is the mnemonic? |
Did king phillip come over for group sex? |
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What new advances have helped us to identify evolutionary relationships between organisms? |
Immunology and genome sequencing - comparing genetic diversity(the more similar the sequences being compared the more closely related as mutations of DNA result in speciation and mutations accumulate overtime so become less related) |
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What do phylogenetic trees show? |
Evolutionary relationships including how closely related a species is with the most common (oldest) ancestors at the base. Closer branches = more related |
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Define selection |
The process in which organisms that are better adapted to an environment will survive and breed and those who are not will die out |
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What do the same species possess that enables them to identify eachother? |
Same genes which physical , biochemical characteristics and behaviour which are all the same - so can identify one another to mate |
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What is behaviour determined by? |
Genetics |
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Why is courtship essential? |
Needs to occur for mating to occur as organisms can recognise members of their own species and can determine if the partner is suitable (e.g. fertile) so the mating will be a success. Mating leads to survival of a species as the population is increased |
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What are the 3 essential things needed in courtship for mating to be successful? |
Recognising members of your species so mating occurs within a species so fertile offspring are produced , whether the female is capable of breeding in that specific time frame -fertile and forming a pair bond - for raising offspring - ensures their survival |
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What makes a female fertile? |
Whether she is in season and whether she is sexually mature |
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Why is the pair bond important? |
They will mate and protect the offspring to ensure their survivol |
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What does the male do and what does the female do? |
The male initiates and the female responds (behaviour determined by genetics so correct responses determine if same species so successful mating can occur) |
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What if the female doesnt respond correctly? |
The male will turn his attentions elsewhere |
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What is biodiversity? |
The number and variety of genes species and habitats in a particular region (any habitat) Greater species diversity , genetic diversity and ecosystem diversity = greater biodiversity |
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What is species diversity? |
The number of species and the number of individuals that make up these species within a community |
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What is species richness? |
The number of different species in a community (one component of species diversity) |
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What is ecosystem diversity? |
The range of habitats that exist within a certain area |
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What is the formula to calculate index of diversity? |
d= N(N-1) / sum of n(n-1) |
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What does N stand for? |
Total number of organisms in the community - of all the species |
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What does n stand for? |
Total number of individuals of the individual species |
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What does it mean the larger the value for species diversity is? |
The more diverse the habitat is (in terms of species) |
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Why is the formula important? |
It takes into account the proportions of each species and not just how many species and the total number of organims |
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What does agriculture result in? |
The reduction of biodiversity |
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What is the word for an agriculture ecosystem? |
A mono-culture |
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Why? |
One desirable species is favoured |
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Why are monocultures different to natural communities? |
Controlled by humans who select desirable species and exclude other species using pesticides etc |
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What else other than biodiversity decreases? |
Genetic diversity |
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What are the minority species left to do? |
Compete over small space and few resources |
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What does this result in? |
Some die or have very small populations |
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What do farmers use which exclude species? |
Pesticides and herbicides |
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What is the species diversity value like in agricultural ecosystems? |
Low |
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3 direct ways of reducing biodiversity? |
Removing woodland , filling in ponds and overgrazing land via animals |
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What do we try to get a good balance between? |
Conservation and farming |
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What do the management techniques for this do? |
Increase species diversity and habitats without raising food costs or lowering yields |
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What are the 8 ways? |
Hedgerows are grown around fields , ponds are kept , wet corners on fields are untouched , trees of low diversity are planted , use of pesticides and herbicides are reduced , organic fertilisers are used , crop rotation and intercropping takes place , allow wild insects and flowers to breed at the edges of fields , natural meadows and more ponds are created |
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Removing habitats also removes... |
Food sources |
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Why are many samples from different areas taken? |
To obtain a reliable mean |
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Why do we compare species and inviduals? |
To determine evolutionary relationships by looking at genetic diversity (same alleles more related , less alleles the same - more diverse less related) |
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What are the four ways we can do this? |
Frequency of observable characteristics , DNA base sequences , mRNA base sequences and amino acid sequences |
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Why do we can compare observable characteristics? |
They are determined by genes so if individuals have same characteristics we can conclude they have the same genes |
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Problems with this? |
Characteristics are coded for by multiple different genes and characteristics are influenced by environmental factors |
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How can we compare DNA , mRNA and AA ? |
Count number of similarities and number of differences. The more similarities the more closely related |
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Why do differences in these sequences increase over time? |
Mutations occur |
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What is interspecific variation? |
Two species being different |
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What is intraspecific variation? |
Two individuals of the same species being different |
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What do scientists use when making measurements? |
Samples |
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What must the sample be and why? |
Representative of the whole population so we can generalise and our results will be reliable |
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What problems do scientists face which make a sample unrepresentative? |
Sampling bias and chance |
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What is sampling bias? |
Picking samples that will give unrepresentative results such as certain areas , manipulating data |
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How do you eliminate sampling bias? |
Remove human involvement. E.g. us a computer to generate coordinates |
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How can chance make results unrepresentative? |
By chance you pick an area with lots of one type of flower , this doesnt represent whole population |
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How can you eliminate chance? |
You cannot but you can reduce its effects by using a large sample size for less anomaly influence and use a statistical tests as they take chance into account and you can see a statistical significance |
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What does skewed data look like on a normal distribution? |
It is shifted with different values for mean median and mode |
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How does this compare to a symmetrical distribution? |
Mean median and mode all have very similar values |
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How is the mean and standard deviation represented on a normal distribution? |
The mean is the maximum height and the standard deviation is the width to the point of inflexion |
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What proportion of the data is within one standard deviation of the mean? |
68% |
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1.96 standard deviations of the mean? |
95% |
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How is standard deviation represented on bar charts? |
Capital I , its an error bar |
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If the error bar is really large what does it mean? |
The greater the range of values in the sample |
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When you compare two standard deviations what do you look for? |
Overlap |
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If standard deviations overlap... |
It is not statistically significant and is due to chance |
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If they don't overlap... |
Statistical significancr and the results are due to another factor and not chance |
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How sure do we need to be that results are not due to chance? |
95% |
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What is a null hypothesis? |
The opposite of what you are tryinf to prove |
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Why do we use a null hypothesis? |
Easier to disprove than prove what you're looking for |
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What are the three statistical tests? |
CHI^2 , students T , correlation coefficient |
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How do you decide which test is approriate? |
If the data is frequencies use CHI^2 , if it is measurements and there are two variables use correlation coefficient , if it is simply measurements use students T test |
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How does the CHI^2 test work? |
State a null hypothesis , calculate an expected frequency compared to observed frequency. Calculate a chi value and degrees of freedom . Look up critical value for 5% , if chi value exceeds critical value then you can reject null hypothesis as there is statistical significance |
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How does the correlation coefficent work? |
State null hypothesis. Rank data , work out coefficient it will be between -1 and 1 which shows nature of correlation. Look up critical value for 5% and if coefficent exceeds critical value reject null hypothesis as this is statistically significant |
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What does the students T test compare? |
The mean of two sets of data |
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What is the phrase to use when concluding for statistical test? |
There is a 95% probabibility the results are not due to chance , this is statistically significant so we can reject the null hypothesis |
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What does the fact that DNA is universal mean? |
All triplets code for the same amino acids in all organisms |
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What are the 2 different types of non-coding DNA? |
Introns within genes that are removed via splicing when translation occurs. Also VNTRs - non-coding multiple repeats which exists between genes |
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What is an example of how our DNA controls our appearance (in detail) ? |
Allele of a gene codes for a specific enzyme which catalyses the production of a pigment to give us a hair colour - |
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When are chromosomes of a cell visible under a microscope ? Why do they look like this? |
When mitosis is occuring (any stage that is not interphase as nuclear envelope broken down) two chromatids joined at the centromere due to replication in DNA - chromatids seperated in division |
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Why is mRNA being broken down after translation an advantage? |
Protein would keep being produced which is wasteful when we dont need it. Only transcribed when needed and then broken down |
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What occurs to the exposed template of DNA as RNA polymerase moves along in transcription? |
DNA rejoins behind it after being transcribed which limits exposure of bases |
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Can multiple ribosomes act on one mRNA at once? |
Yes so identical polypeptides can be synthesised simultaneously |
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Role of ATP in translation? |
Attach amino acids to tRNA and to attach amino acids together (form peptide bonds) |
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Why do we say the nucleus controls the cells activities? |
DnA produces enzymes which catalyse many biological processes |
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What parts of meiosis directly produce genetic variation? |
Independent segregation of homologous chromosomes leads to gametes with different alleles - crossing over mixes up paternal and maternal further increasing allele combos Random fertilisation further increases variety as 2 gametes containing different alleles fuse |
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What is a gene pool? |
The total number of alleles in a particular population (natural selection causes alleic frequencies of certain alleles to change within the gene pool) |
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Define selection. |
Organisms better adapted to their environment will survive and breed (natural , artificial is where humans pick specific organisms to survive and breed) |
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What happens if the selection pressure changes are too great? |
No individuals suited and the entire population dies out |
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What is the end result of natural selection? |
Evolution to produce a species better adapted to survive (adaptations can be anatomical physiological or behavioural) |
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What makes it difficult to classify the species of an organism based on the definition of a species? |
Some organism are infertile / dont produce asexually Speciation occurs so dont know if variation = multiple species or just extreme variation from artificial selection to produce pedigrees for example. Hard to conclude from fossil records. Geographically isolated organisms do not have the chance to breed eventhough they can |
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What does index of diversity represent mathematically? |
Species diversity as it takes species richness and individual numbers of each species into account |
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What does having a diverse ecosystem say about its function? |
More diverse = more stable so it is less effected by changes. As it is much more likely a species that can survive the changes will be present so a population/community can be maintained in this area |
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Harsh environments tend have lower.... |
Index of diversity as species need adaptations in order to survive - environment dominates not species |
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What does 2 x SD overlap between groups mean in terms of chance? |
95% probability any difference is due to chance |
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How can you choose a suitable SD for data given a choice? |
2 x SD will include most data as by definition is 95% |
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Why is the triplets for each AA given as mRNA codons rather than DNA triplets? |
DNA is double stranded and only one strand is used to produce mRNA , proteins produced directly from mRNA |
