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topic 4 Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

differences between DNA and RNA

A 
DNA:
-double stranded
-contains the base thymine
-contains deoxyribose sugar
-much longer than RNA
-found in the nucleus
RNA:
-single stranded
-contains the base uracil
-contains ribose sugar 
-shorter than DNA
-found in the cytoplasm
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2
Q

what are nucleotides and what do they consist of

A

nucleotides are the monomers that make up DNA and RNA. they join together in condensation reactions by phosphodiester bonds.
they consist of pentose, a nitrogenous base and a phosphate group.

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3
Q

features of the genetic code

A

genetic code - order of bases on DNA

  • universal so all known living organisms use the same genetic code.
  • non overlapping so each triplet is only read once and triplets don’t share any bases
  • genes are separated by non-coding multiple repeats of base sequences
  • degenerate so more than one triplet codes for one amino acid
  • contains stop and start codons
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4
Q

what are non-coding and coding sections of DNA called

A

non-coding - introns

coding - exons

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5
Q

what is a gene

A

the sequence of bases on a DNA molecule coding for a sequence of amino acids in a polypeptide chain. it occupies a fixed position called a locus on a particular DNA molecule

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6
Q

DNA in eukaryotic cells vs prokaryotic cells

A

eukaryotic cells:
-the DNA molecules are found in the nucleus and are long and linear.
-they wind around proteins called histones to fit in the nucleus.
-the DNA and histone coil very tightly to form chromosomes.
-the mitochondria and chloroplasts contain short circular DNA.
prokaryotic cells:
-the DNA is short and circular and not associated with proteins.
-condenses to fit in the cell by supercoiling

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7
Q

what is the genome

A

the complete set of genes in the cell

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8
Q

what is the proteome

A

the full range of proteins that the cell is able to produce

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9
Q

allele

A

a different form of a gene

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10
Q

describe a homologous pair of chromosomes

A

both chromosomes are the same size and have the same genes but could have different alleles

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11
Q

describe mRNA

A
  • made during transcription
  • carries the genetic code from the DNA to the ribosomes where it is used to make proteins during translation
  • it is a single-stranded linear molecule
  • groups of 3 adjacent bases are called codons
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12
Q

describe tRNA

A
  • involved in translation
  • carries amino acids that are used to make proteins to the ribosomes
  • it is a single-stranded molecule folded into a cloverleaf shape.
  • held together by H bonds between specific base pairs
  • anticodon at one end of the molecule and an amino acid binding site on the other end.
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13
Q

describe the process of transcription

A

transcription is the process where a DNA strand acts as a template to form a complementary mRNA strand
in prokaryotes, this occurs in the cytoplasm
in eukaryotes, this occurs in the nucleus
-an enzyme called DNA helicase breaks the H bonds between the two strands in a DNA double helix causing the DNA to unwind, exposing its bases.
-one strand known as the antisense is used as a template to make an mRNA copy.
-free floating nucleotides line up according to complementary base pairing with the DNA template strand except uracil replaces thymine.
-this forms mRNA
-the enzyme RNA polymerase catalyses the formation of phosphodiester bonds between each base in the mRNA strand, forming an mRNA molecule
-when the RNA polymerase reaches a stop codon, the mRNA stops being made

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14
Q

mRNA produced is eukaryotes vs prokaryotes

A
  • in eukaryotes, the introns and exons are both copied into mRNA during transcription.
  • mRNA containing introns and exons is called pre-mRNA.
  • the pre-mRNA is spliced by spliceosomes to remove introns.
  • the mRNA then moves out of the nucleus through nuclear pores and attaches to a ribosome in the cytoplasm.
  • in prokaryotes, mRNA is produced directly from the DNA.
  • splicing doesn’t take place because the mRNA doesn’t contain introns.
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15
Q

what are gametes

A

sex cells

sperm and egg cell

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16
Q

what is a zygote

A

a fertilised egg in early stages of development

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17
Q

diploid

A

normal body cells have the diploid number of chromosomes so each cell contains two of each chromosome.

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18
Q

haploid

A

gametes have a haploid number of chromosomes - there’s only one copy of each chromosome.

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19
Q

describe the process of translation

A

when the polypeptide chain is produced

  • once the modified mRNA has left the nucleus, it attaches to a ribosome in the cytoplasm
  • the ribosome attaches at the start codon
  • free tRNA molecules bind with their specific amino acids in the cytoplasm and bring them to the mRNA molecule on the ribosome
  • The triplet of bases (anticodon) on each tRNA molecule pairs with a complementary triplet (codon) on the mRNA molecule
  • Two tRNA molecules fit onto the ribosome at any one time, bringing the amino acid they are each carrying side by side
  • A peptide bond is then formed between the two amino acids
  • The formation of a peptide bond between amino acids requires energy, in the form of ATP
  • The ATP needed for translation is provided by the mitochondria within the cell
  • This process continues until a ‘stop’ codon on the mRNA molecule is reached – this acts as a signal for translation to stop and at this point the amino acid chain coded for by the mRNA molecule is complete
  • This amino acid chain then forms the final polypeptide
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20
Q

what is rRNA

A

ribosomal RNA makes up the bulk of ribosomes

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21
Q

what is the purpose of meiosis

A

-consists of two nuclear divisions which results in the formation of four haploid daughter cells from a single diploid parent cell that are genetically different

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22
Q

how does meiosis introduce variation

A

-independent segregation
-crossing over
both occur in the first round of division

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23
Q

how many chromosomes are in each division

A

46–>92—> two cells, each with 46–> 4 cells each with 23

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24
Q

describe crossing over

A

during meiosis 1, homologous pairs of chromosomes come together and pair up. the chromatids on each chromosome twist around each other and sections of the chromatids swap over. the chromatids still have the same genes but now have a different combination of alleles. this increases genetic variation.

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25
Q

describe independent segregation of chromosomes

A
  • when the homologous pairs are separated in meiosis 1, it is completely random which chromosome from each pair ends up in which daughter cell
  • this means that the 4 daughter cells have completely different combinations of the maternal and paternal chromosomes.
  • this leads to genetic variation.
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26
Q

how does random fertilisation increase genetic variation

A

during sexual reproduction, fertlisation is random so any sperm cell can fertilise any egg cell. this produces zygotes with different combinations of chromosomes to both parents and increases genetic variation.

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27
Q

what are the different outcomes from meiosis and mitosis

A
  • mitosis produces cells with the same number of chromosomes as the parent cell whereas meiosis produces daughter cells with half the number of chromosomes as the parent cell.
  • in mitosis, the daughter cells are genetically identical to each other and the parent cell. in meiosis, each daughter cell is genetically different from each other and the parent cell.
  • mitosis produces two daughter cells whereas meiosis produces four daughter cells.
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28
Q

why do mitosis and meiosis have different outcomes

A
  • mitosis only consists of one division whereas meiosis consists of two.
  • no pairing or separating of homologous pairs of chromosomes and so no crossing over or independant segregation. therefore, they are all genetically identical.
29
Q

describe chromosome mutations

A
  • caused by errors during meiosis

- lead to inherited conditions

30
Q

what are gene mutations

A
  • a change in the DNA base sequence of chromosomes
    e. g. through substitution or deletion
  • as the DNA base sequence determines the sequence of amino acids that make up a protein, mutations in a gene can sometimes lead to a change in the polypeptide that the gene codes for
31
Q

why don’t all mutations affect the order of amino acids

A
  • the genetic code is degenerate so some amino acids are coded for by more than one DNA triplet
  • this means not all substitution mutations will result in a change to the amino acid sequence because the new DNA triplet may still code for the same amino acid.
  • however deletion will change the amino acid sequence as all of the bases after the deleted base will shift
32
Q

mutagenic agents

A

mutagenic agents increase the rate of mutations. e.g. UV radiation, ionising radiation and some chemicals

33
Q

define genetic diversity

A

the number of different alleles of genes in a species or population

34
Q

describe polyploidy

A
  • changes in whole sets of chromosomes occur when organism have 3 or more sets of chromosomes rather than the usual 2.
  • this mainly occurs in plants
35
Q

describe aneuploidy

A
  • changes in the number of individual chromosomes
  • homologous pairs of chromosomes fail to separate properly. this is called non-disjunction.
  • in humans this can lead to down syndrome
  • this happens when a person has an extra copy of chromosome 21
36
Q

describe natural selection

A
  • organisms within a population show genetic variation due to random mutations creating new alleles.
  • a change in the environment changes the selection pressures acting on the population.
  • an allele may provide a selective advantage
  • individuals with the allele are more likely to survive, reproduce and pass on the allele to their offspring.
  • this causes the allele frequency to change. therefore, evolution has occured.
37
Q

define allele frequency

A

the proportion of organisms in the population carrying a particular allele

38
Q

define evolution

A

a change in the allele frequency of a population over many generations.

39
Q

define mutation

A

a change in an organisms DNA. may result in the production of a different protein.

40
Q

define gene pool

A

all the alleles of all the genes present in a population

41
Q

define selection pressures

A

a condition driving natural selection

42
Q

define selective advantage

A

individuals that have the advantageous allele for survival.

43
Q

shared characteristics that suggest a shared origin of all life on earth

A
  • all have DNA or RNA as their genetic material
  • the genetic code is universal
  • ATP is the universal molecule for immediate energy
  • the proteins in all organisms are formed from the same 20 amino acids.
  • all have phospholipid membranes
  • vital physiological processes follow very similar metabolic pathways in all organisms.
44
Q

factors needed for a population to be able to evolve

A

genetic variation- must be differences between the individuals in a population that are inheritable.
means of selection- must be a pressure that selects some variables for the next generation at the expense of others

45
Q

describe discontinuous variation

A
  • limited number of traits, no intermediate forms
  • controlled by a few genes, usually with multiple alleles
  • environment has little effect on these characteristics
  • can be represented by a bar chart
    e. g. human blood groups, antibiotic resistance
46
Q

describe continuous variation

A
  • range of gradation of characteristics
  • controlled by many genes (polygenic)
  • environment has a significant effect
  • can be represented by a histogram
  • e.g. stem height in plants, milk yield in cows
47
Q

define phenotype

A

an organisms observable traits

48
Q

define genotype

A

the complete set of genetic material in an organism

49
Q

2 types of selection

A

stabilising and directional

50
Q

define stabilising selection

A

individuals with alleles for characteristics towards the middle of the range are more likely to survive and reproduce. it occurs when the environment isn’t changing and it reduces the range of possible characteristics.

51
Q

define directional selection

A

individuals with alleles for characteristics of an extreme type are more likely to survive and reproduce. this could be in response to an environmental change

52
Q

describe the selection shown by human birth weight

A
  • shows stabilising selection
  • humans have a range of birth weights
  • very small babies are less likely to survive - partly because they find it hard to maintain their body temperature
  • giving birth to large babies can be difficult, so large babies can be difficult, so large babies are less likely to survive too.
  • conditions are most favourable for medium-sized babies- so weight of human babies tends to shift towards the middle of the range.
  • this causes the curve to narrow
53
Q

describe the selection shown by antibiotic selection

A
  • shows directional selection
  • some individuals in a population have alleles that give them resistance to an antibiotic
  • the population is exposed to the antibiotic so the bacteria without antibiotic resistance are killed
  • the resistant bacteria survive and reproduce passing on the antibiotic resistance allele to their offspring
  • after some time, most organisms will carry the antibiotic resistance allele.
  • this causes the curve to shift to the extreme side (high antibiotic resistance)
54
Q

what is a species

A

a group of similar organisms that can breed to produce fertile offspring

55
Q

what is the order of classification

A 
Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species
(do keep ponds clean or frogs get sick)
-used to understand relationships between organisms and keep track of changes 
-it is universal
56
Q

describe the binomial system

A
  • has two parts
  • the first is the genus name and it has a capital letter
  • the second is the species name and it has a lower case letter
57
Q

describe courtship

A
  • carried out by organisms to attract a mate of the same species
  • it is specific to the species so allows members of the same species to recognise each other and prevent interbreeding so they can produce fertile offspring
  • courtship behaviour can be used to classify different organisms
  • closely related species have similar courtship behaviour
58
Q

different techniques to clarify evolutionary relationships

A

genome sequencing, comparing amino acid sequence and immunological comparisons

59
Q

describe genome sequencing

A

-the entire base sequence of an organism’s DNA can be determined and compared to the DNA base sequence of another organisms to see how closely related they are.

60
Q

describe comparing amino acid sequence

A
  • the sequence of amino acids that make up a protein is determined by the base sequence of the organism’s DNA.
  • closely related organisms have similar DNA sequences so will also have similar amino acid sequences in their proteins
61
Q

describe immunological comparisons

A

-similar proteins will bind to the same antibodies

62
Q

how were early estimates of genetic diversity made

A
  • looking at the frequency of measurable or observable characteristics in a population
  • as alleles determine characteristics, the more characteristics in a population, the more alleles so their is higher genetic diversity
63
Q

what is variation and how is it caused

A
  • the differences that exist between individuals
  • there is variation between species and within species
  • can be caused by genetic factors. different species have different genes, members of the same species have different alleles.
  • variation within a species can also be caused by differences in the environment
  • most variation is caused by a combination of the two.
64
Q

define biodiversity

A

-the variety of living organisms in an area

65
Q

define a habitat

A

-the place where an organism lives

66
Q

define community

A

-all the populations of different species in a habitat

67
Q

define species richness

A
  • a measure of the number of different species in a particular area at the particular time.
  • can be worked out by taking random samples of a community and counting the number of different species
68
Q

examples of conservation techniques

A
  • legal protection to endangered species
  • creating protected areas
  • schemes to encourage farmers to conserve biodiversity
69
Q

what is a hierachy

A

-small groups arranged in larger groups with no overlap between groups

Biology (9 decks)

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