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a level biology > topic 4 > Flashcards

topic 4 Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

Describe the characteristics of nuclear eukaryotic DNA

A

-Linear
-Associated with histones
-Larger than prokaryotic DNA
-Really long so wound up and coiled tightly into chromosomes to fit into the nucleus

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2
Q

Describe the characteristics of prokaryotic DNA

A

-shorter
-circular
-not associated with histones - condenses into cell by supercoiling

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3
Q

What is a gene?

A

a sequence of DNA bases that codes for either a polypeptide or functional RNA

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4
Q

What is a cell’s genome?

A

the complete set of genes in the cell

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5
Q

What is a cell’s proteome?

A

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

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6
Q

What are introns? What happens to them during protein synthesis?

A

Introns are sections of genes that do not code for amino acids
Introns are therefore not useful for protein synthesis and are spliced out of the gene

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7
Q

What are exons?

A

sections of a gene that do code for amino acids

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8
Q

What is an allele?

A

alleles are different forms of a gene. they code for slightly different versions of the same polypeptide
e.g. the gene for blood type exists in 3 different alleles - type A, B, and O

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9
Q

What are homologous pairs of chromosomes?

A

pairs of chromosomes that are the same size, have the same genes, but could have different alleles. Alleles coding for the same characteristic will be found at the same fixed position (locus) on each chromosome in a homologous pair

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10
Q

What is mRNA? What does it do?

A

mRNA (messenger RNA) is made during transcription and it carries the genetic code from the DNA to the ribosomes, where its used to make a protein during translation

mRNA is a single polynucleotide strand, groups of 3 bases are called codons

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11
Q

What is tRNA? What does it do?

A

tRNA (transfer RNA) is involved in translation - it carries the amino acids that are used to make proteins to the ribosomes.

tRNA is a single polynucleotide chain that’s folded into a clover shape. Hydrogen bonds between specific base pairs hold the molecule in this shape

Every tRNA molecule has a specific sequence of 3 bases at one end called the anticodon

They also have an amino acid binding site at the other end

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12
Q

Describe the steps involved in transcription of protein synthesis

A
  1. RNA polymerase attaches to the DNA double-helix at the beginning of a gene
  2. Hydrogen bonds between the 2 DNA strands in the gene are broken by DNA helicase attached to the RNA polymerase. This separates the strands and the DNA molecule uncoils at that point, exposing some of the bases
  3. One of the strands is then used as a template to make an mRNA copy
  4. 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. Complementary base pairing means that the mRNA strand ends up being a complementary copy of the DNA template strand (expect the T is replaced with a U in RNA)
  5. The nucleotides are joined with the DNA bases by RNA polymerase, forming phosphodiester bonds to form an mRNA molecule

6.RNA polymerase moves along DNA, separating the strands + assembling the mRNA strand

  1. The hydrogen bonds between the uncoiled DNA strands reform once RNA polymerase has passed by and the strands coil back into a double-helix

8.When RNA polymerase reaches a particular sequence of DNA called a stop signal, it stops making mRNA and detaches from the DNA

9.In eukaryotes, mRNA moves out of the nucleus through a nuclear pore and attaches to a ribosome in the cytoplasm.

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13
Q

How is transcription different in eukaryotes and prokaryotes?

A

Eukaryotes - introns + exons both copied into mRNA (pre-mRNA). A process called splicing occurs where introns are removed from mRNA strand and the exons are joined together, making mRNA.

Prokaryotes - mRNA directly from DNA without splicing taking place, as there is no introns in prokaryotic DNA

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14
Q

Describe the steps involved in translation of protein synthesis

A
  1. The mRNA attaches itself to a ribosome and tRNA molecules carry amino acids to it. ATP provides the energy needed for the bond between the amino acid and the tRNA molecule to form
  2. A tRNA molecule, with an anticodon complementary to the first codon on the mRNA attaches itself to the mRNA by specific base pairing

3, A second tRNA molecule attaches itself to the next codon on the mRNA in the same way

  1. The 2 amino acids attached to the tRNA molecules are joined by a peptide bond. The first tRNA molecules moves away, leaving its amino acid behind
  2. A 3rd tRNA molecule binds to the next codon on the mRNA. Its amino acid binds to the first 2 and the second tRNA molecule moves away
  3. This process continues, producing a polypeptide chain, until there’s a stop signal on the mRNA molecule
  4. The polypeptide chain moves away from the ribosome and translation is complete
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15
Q

What is the genetic code?

A

the sequence of base triplets (codons) in mRNA which code for specific amino acids

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16
Q

Describe the characteristics of the genetic code

A

Non-overlapping = each base triplet is read in sequence, separate from the triplet before and after it.

Degenerate = there are more possible combinations of triplets than there are amino acids. Means some amino acids are coded for by more than 1 base triplet.

Universal = the same triplets code for the same amino acids in all living things

17
Q

What are gametes?

A

-Sperm cells in males, egg cells in females - join together in fertilisation to form a zygote, which divides and develops into a new organism

-haploid cells - only have 1 copy of each chromosome

18
Q

Describe meiosis

A
  1. Before meiosis, DNA replicates so there are 2 copies of each chromosome, called chromatids

2.DNA condenses to form double-armed chromosomes. Sister chromatids joined by a centromere

3.Meiosis I (first division) - chromosomes arrange themselves into homologous pairs

4.Homologous pairs then separated, halving the chromosome number

5.Meiosis II (second division)
- pairs of sister chromatids separate (centromere is divided)

  1. 4 haploid cells that are genetically different from each other are produced
19
Q

Explain how genetic variation occurs in meiosis

A
  1. Crossing over of chromatids - parts of chromatids twist around each other and swap parts - all 4 haploid cells contain chromatids with different alleles

2.Independent segregation of chromosomes - each homologous pair contains 1 maternal and 1 paternal chromosome
-when separated, its completely random which chromosome ends up in which daughter cell
- all 4 daughter cells have different combinations of those maternal + paternal chromosomes

20
Q

What is non - disjunction of chromosomes?

A

the failure of chromosomes to separate, one cell will get an extra copy of a chromosome whilst the other gets none

21
Q

Explain the types of gene mutations that cause changes to the DNA base sequence

A

-Substitution - one base is substituted with another

-Deletion - one base is deleted

22
Q

Why can substitution sometimes have no effect on the order of amino acids?

A

Degenerate nature of the genetic code - means some amino acids are coded for by more than 1 DNA base triplet, some substitutions will still code for the same amino acid as the original DNA base triplet

23
Q

What are mutagenic agents?

A

Substances that can increase the rate of DNA mutations e.g. ultraviolet radiation and ionising radiation

24
Q

What is gene flow?

A

different alleles being introduced into a population, when individuals from another population migrate into them and reproduce

25
Q

What is a genetic bottleneck?

A

An event that causes a big reduction in a population e.g. when a large number of organisms die before reproducing

This reduces the number pf different alleles in the gene pool and so reduces genetic diversity

The survivors reproduce and a larger population is created from a few individuals

26
Q

What is the founder effect?

A

A type of genetic bottleneck which describes what happens when just a few organisms from a population start a new colony and there are only a small number of different alleles in the initial gene pool

the frequency of each allele in the new colony may be very different to the frequency of those alleles in the original population - e.g. an allele that was rare in the original population might be more common in the new colony

The founder effect can occur as a result of migration

27
Q

Explain the process of natural selection

A

Randomly-occurring mutations can result in a new allele being formed that gives the organism a beneficial characteristic that increases the organism’s survival chances

This means organisms without this allele are more likely to die, so organisms with the advantage are likely to survive and reproduce

This means that a greater proportion of the next generation inherits the beneficial allele

The frequency of this allele increases from generation to generation eventually leading to evolution as the advantageous alleles become more common in the population

28
Q

What are the 3 types of adaptations?

A
  • behavioural - ways as organism acts that increases survival/reproduction rates

-physiological - processes inside an organism’s body that increase survival rates

-anatomical - structural features of an organism’s body that increase survival rates

29
Q

What is selection pressure in a population?

A

the environmental force altering the frequency of alleles in a population

30
Q

What is directional selection?

A

alleles for characteristics of an extreme type are more likely to survive and reproduce
e.g. antibiotic resistant bacteria

31
Q

What is stabilising selection?

A

when selection pressures on a population cause more individuals near the average phenotype to survive and reproduce

32
Q

What is phylogenetic classification of organisms?

A

arranges species into groups based on their evolutionary origins and relationships

uses a hierarchy where smaller groups are placed into larger groups, with NO overlap between groups

each group is called a taxon

The taxa included in the hierarchy: Domain, Kingdom, Phylum, Class, Order, Family, Genus, and Species

33
Q

what is the binomial naming system?

A

first part of name is the genus, has a capital letter

second part of name is the species, has a lower case letter

e.g. Homo sapiens

34
Q

What is courtship behaviour?

A

carried out by organisms to attract a mate of the right species

This behaviour is species specific - only members of the same species will do and respond to that behaviour

35
Q

What is species richness?

A

a measure of the number of different species in a community

36
Q

What is an index of diversity?

A

describes the relationship between the number of species in a community and the number of individuals in each species

37
Q

How do you calculate index of diversity?

A

d = N ( N - 1 )
over
‘sum of’ n ( n - 1 )

where N = total number of organisms of ALL species

n = total number of organisms of ONE species

the higher the number, the more diverse the area

38
Q

How do agricultural practices reduce biodiversity?

A

woodland clearance - increase farmland area
-reduces number of trees + tree species
-destroys habitats, species lose shelter + food

hedgerow removal -
-increase farmland area by turning many small fields into fewer larger ones
-reduces biodiversity for same reasons as woodland clearance

pesticides/herbicides
-kill unwanted pests that feed on crops/ unwanted plants
-reduces diversity
-food sources lost
-reduces their numbers

Monoculture-
-farms with fields containing only one type of plant
-reduces biodiversity
-supports fewer organisms which further reduces diversity

39
Q

How do we find out genetic diversity of organisms?

A

Comparing DNA base sequences can be used to see how closely related organisms are.

Comparing amino acid sequences - amino acids are coded for by the base sequence in DNA .

a level biology (12 decks)

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