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A Level Biology > Topic 4 > Flashcards

Topic 4 Flashcards

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1
Q

How are DNA molecules structured in eukaryotic cells?

A

DNA molecules are very long, linear, and associated with histone proteins,

forming tightly coiled compact chromosomes.

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2
Q

How is DNA structured in prokaryotic cells?

A

DNA molecules are short, circular, and not associated with proteins.

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3
Q

What type of DNA do mitochondria and chloroplasts contain in eukaryotic cells?

A

The mitochondria and chloroplasts of eukaryotic cells contain DNA that is short, circular, and not associated with proteins, similar to the DNA of prokaryotes.

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4
Q

What is a gene and what does it code for?

A

A gene is a base sequence of DNA that codes for the amino acid sequence of a polypeptide or a functional RNA (including ribosomal RNA and tRNAs).

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5
Q

What is a locus in the context of genetics?

A

A locus is a fixed position on a particular DNA molecule where a gene is located.

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6
Q

What is a triplet in DNA, and what is its significance?

A

A triplet is a sequence of three DNA bases that codes for a specific amino acid.

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7
Q

What are the three main characteristics of the genetic code?

A

The genetic code is universal, non-overlapping, and degenerate.

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8
Q

How much of the nuclear DNA in eukaryotes codes for polypeptides?

A

In eukaryotes, much of the nuclear DNA does not code for polypeptides, and there are non-coding multiple repeats of base sequences between genes.

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9
Q

Differentiate between exons and introns.

A

Exons are sequences within a gene that code for amino acid sequences,

while introns are non-coding sequences that separate the exons within a gene.

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10
Q

What is the genome?

A

The genome is the complete set of genes in a cell.

It contains all the genetic information necessary for the structure, function, and regulation of the organism’s cells, tissues, and organs.

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11
Q

What is the proteome?

A

The proteome is the full range of proteins that a cell is able to produce.

This includes all the proteins expressed by the genome, under specific conditions and at a particular time.

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12
Q

Describe the structure of messenger RNA (mRNA).

A

Messenger RNA (mRNA) is a single-stranded molecule that carries genetic information from DNA to the ribosome,

where proteins are synthesized.

It consists of a series of nucleotides, each comprising a ribose sugar, a phosphate group,

and one of four nitrogenous bases (adenine, uracil, cytosine, and guanine).

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13
Q

Describe the structure of transfer RNA (tRNA).

A

Transfer RNA (tRNA) is a small RNA molecule that helps decode mRNA into a protein.

It has a cloverleaf structure with an anticodon loop that pairs with the complementary codon on mRNA and an attached amino acid at the opposite end.

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14
Q

What is transcription?

A

Transcription is the process of producing mRNA from DNA.

During transcription, RNA polymerase binds to DNA at the promoter region and synthesizes mRNA

by joining RNA nucleotides that are complementary to the DNA template strand.

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15
Q

How does transcription differ in prokaryotes and eukaryotes?

A

In prokaryotes, transcription directly produces mRNA from DNA. In eukaryotes,

transcription results in the production of pre-mRNA, which is then spliced to remove introns and join exons,

forming mature mRNA.

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16
Q

What is translation?

A

Translation is the process of synthesizing polypeptides (proteins) from the sequence of codons carried by mRNA.

Ribosomes facilitate this process, and tRNA molecules bring the appropriate amino acids to the ribosome,

where they are joined together using energy from ATP.

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17
Q

What roles do ribosomes, tRNA, and ATP play in translation?

A

Ribosomes serve as the site of protein synthesis,

reading the mRNA sequence and facilitating the assembly of amino acids into polypeptides.

tRNA molecules transport specific amino acids to the ribosome, matching their anticodon with the corresponding mRNA codon.

ATP provides the energy required for the formation of peptide bonds between amino acids.

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18
Q

What are gene mutations?

A

Gene mutations involve a change in the base sequence of chromosomes

and can arise spontaneously during DNA replication.

They include base deletion and base substitution.

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19
Q

How does the degenerate nature of the genetic code affect base substitutions?

A

Due to the degenerate nature of the genetic code,

not all base substitutions cause a change in the sequence of encoded amino acids.

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20
Q

What role do mutagenic agents play in gene mutations?

A

Mutagenic agents can increase the rate of gene mutation.

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21
Q

How can mutations in the number of chromosomes arise?

A

Mutations in the number of chromosomes can arise spontaneously by chromosome non-disjunction during meiosis.

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22
Q

What is the outcome of meiosis?

A

Meiosis produces daughter cells that are genetically different from each other.

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23
Q

What happens during the two nuclear divisions in meiosis?

A

Two nuclear divisions usually result in the formation of four haploid daughter cells from a single diploid parent cell.

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24
Q

How do genetically different daughter cells result from meiosis?

A

Genetically different daughter cells result from the independent segregation of homologous chromosomes during meiosis.

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25
Q

outline the process of crossing over in meiosis

A
  1. Homologous pairs of chromosomes associate and form a bivalent;
  2. Chiasmata forms;
  3. Equal lengths of non-sister chromatids or alleles are exchanged;
  4. Producing new combinations of alleles;
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26
Q

outline independant segregation in meiosis

A
  1. In Metaphase 1, homologous pairs line up either side of the equator.
  2. It is completely random which side of the equator the maternal and paternal chromosomes line up on
  3. When they are separated, one of each pair ends up in a daughter cell
  4. This ‘shuffling’ leads to different combinations of the maternal and paternal chromosomes in daughter
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27
Q

What is genetic diversity?

A

Genetic diversity is the number of different alleles of genes in a population.

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28
Q

Why is genetic diversity important in natural selection?

A

Genetic diversity enables natural selection to occur because it provides a variety of traits that may help individuals survive and reproduce in changing environments.

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29
Q

How can new alleles of a gene arise?

A

New alleles of a gene can arise through random mutations.

30
Q

Are all mutations beneficial?

A

No, many mutations are harmful, but some may be beneficial in certain environments.

31
Q

What happens when a mutation is beneficial?

A

If a mutation is beneficial, it may lead to increased reproductive success for the organism carrying the new allele.

31
Q

How do beneficial alleles spread in a population?

A

Beneficial alleles are inherited by members of the next generation and can increase in frequency over many generations.

32
Q

What is directional selection? Provide an example

A

Directional selection is a type of natural selection that favors one extreme phenotype over others, such as antibiotic resistance in bacteria.

33
Q

What is stabilising selection? Provide an example.

A

Stabilising selection is a type of natural selection that favors intermediate phenotypes and reduces variation, such as human birth weights.

34
Q

How does natural selection result in species adaptation?

A

Natural selection results in species that are better adapted to their environment through anatomical, physiological, or behavioural changes.

new allele formed from mutation

these alleles can be beneficial in organisms survival

more likely to survive and pass on allele to offspring

35
Q

What are the three types of adaptations that can result from natural selection?

A

The three types of adaptations are anatomical (structural), physiological (functional), and behavioural.

36
Q

What defines organisms as belonging to the same species?

A

Organisms belong to the same species if they are able to produce fertile offspring.

37
Q

What is the role of courtship behavior in mating?

A

Courtship behavior is a necessary precursor to successful mating

as it helps in species recognition and ensures that mating occurs between individuals of the same species.

38
Q

What does a phylogenetic classification system aim to represent?

A

A phylogenetic classification system aims to arrange species into groups based on their evolutionary origins and relationships.

39
Q

Describe the hierarchy in phylogenetic classification.

A

the hierarchy in phylogenetic classification consists of taxa arranged in a nested structure:

domain,
kingdom,
phylum,
class,
order,
family,
genus,
species,

with no overlap between groups.

40
Q

How is a species universally identified?

A

A species is universally identified by a binomial name,

consisting of the genus name and species name, e.g., Homo sapiens.

41
Q

What does biodiversity refer to in terms of habitat range?

A

Biodiversity can relate to a range of habitats, from a small local habitat to the entire Earth.

42
Q

What is species richness?

A

Species richness is a measure of the number of different species present in a community.

43
Q

What does an index of diversity describe?

A

An index of diversity describes the relationship between the number of species in a community and the number of individuals within each species.

44
Q

How is the index of diversity (d) calculated?

A

The index of diversity (d) is calculated using the formula:

d= ∑n(n−1) /
N(N−1)

where:
N = total number of organisms of all species

n = total number of organisms of each species.
​

45
Q

How do farming techniques affect biodiversity?

A

Farming techniques generally reduce biodiversity by simplifying ecosystems, often focusing on monoculture crops, using pesticides, and altering natural habitats.

46
Q

What is the balance between conservation and farming?

A

The balance between conservation and farming involves implementing practices that maintain agricultural productivity while conserving biodiversity,

such as crop rotation,

organic farming, and

creating wildlife corridors.

47
Q

How can genetic diversity be assessed within or between species?

A

Genetic diversity can be assessed by comparing:

The frequency of measurable or observable characteristics.

The base sequence of DNA.

The base sequence of mRNA.

The amino acid sequence of the proteins encoded by DNA and mRNA.

48
Q

How does the base sequence of DNA help in measuring genetic diversity?

A

By comparing the sequence of nucleotides (A, T, C, G) in the DNA of different individuals or species,

scientists can determine the level of genetic variation. High variation indicates greater genetic diversity.

49
Q

Why is the base sequence of mRNA used to assess genetic diversity?

A

mRNA sequences, transcribed from DNA, reflect the genes being expressed.

Comparing mRNA sequences reveals differences in gene expression and genetic coding between individuals or species.

50
Q

What is the significance of comparing amino acid sequences in proteins for genetic diversity?

A

Since proteins are directly encoded by DNA via mRNA,

comparing amino acid sequences can show how genetic variations affect protein structure and function,

providing insights into genetic diversity.

51
Q

What is the primary outcome of mitosis?

A

Mitosis results in the production of two genetically identical diploid daughter cells from a single diploid parent cell.

52
Q

What is the primary outcome of meiosis?

A

Meiosis results in the production of four genetically different haploid daughter cells from a single diploid parent cell.

53
Q

How does the genetic composition of daughter cells differ between mitosis and meiosis?

A

In mitosis, daughter cells are genetically identical to the parent cell and each other.

In meiosis, daughter cells are genetically different from the parent cell and each other.

54
Q

What role does mitosis play in the body?

A

Mitosis is responsible for growth, tissue repair, and asexual reproduction in the body.

55
Q

What role does meiosis play in the body?

A

Meiosis is responsible for producing gametes (sperm and eggs) for sexual reproduction.

56
Q

How does random fertilisation of haploid gametes increase genetic variation?

A

Random fertilisation occurs when any sperm can fuse with any egg,

combining different sets of genetic material, which increases genetic variation in the offspring.

57
Q

How many possible combinations of chromosomes can result from the fusion of two gametes due to random fertilisation?

A

Given that humans have 23 pairs of chromosomes,

random fertilisation can result in approximately 70 trillion (2^23 x 2^23) different combinations of chromosomes in the offspring.

58
Q

Why is random fertilisation important for a species?

A

Random fertilisation ensures a high level of genetic diversity within a species,

which is important for adaptation and survival in changing environments.

59
Q

How does random fertilisation interact with other sources of genetic variation?

A

Random fertilisation combines with genetic variation from independent segregation and crossing over during meiosis,

further increasing the genetic diversity of a species.

60
Q

How do advances in immunology help clarify evolutionary relationships?

A

Advances in immunology help clarify evolutionary relationships by allowing scientists to compare immune system proteins and responses across different species, revealing similarities and differences that reflect evolutionary paths.

61
Q

How has gene technology changed the methods of investigating genetic diversity?

A

Gene technology has shifted the focus from inferring DNA differences based on observable characteristics to directly investigating DNA sequences.

62
Q

Define ‘gene mutation’ and explain how a gene mutation can have:

  • no effect on an individual
  • a positive effect on an individual.

(4)

A

(Definition of gene mutation)
1. Change in the base/nucleotide (sequence of chromosomes/DNA);

  1. Results in the formation of new allele;
    (Has no effect because)
  2. Genetic code is degenerate (so amino acid sequence may not change);
    OR
    Mutation is in an intron (so amino acid sequence may not change);
  3. Does change amino acid but no effect on tertiary structure;
  4. (New allele) is recessive so does not influence phenotype;
    (Has positive effect because)
  5. Results in change in polypeptide that positively changes the properties (of the protein)
    OR
    Results in change in polypeptide that positively changes a named protein;
  6. May result in increased reproductive success OR
    May result in increased survival (chances);
63
Q

Describe how a polypeptide is formed by translation of mRNA. (6)

A
  1. (mRNA attaches) to ribosomes OR
    (mRNA attaches) to rough endoplasmic reticulum;
  2. (tRNA) anticodons (bind to) complementary (mRNA) codons;
  3. tRNA brings a specific amino acid;
  4. Amino acids join by peptide bonds;
  5. (Amino acids join together) with the use of ATP;
  6. tRNA released (after amino acid joined to polypeptide);
  7. The ribosome moves along the mRNA to form the polypeptide;
64
Q

Describe how mRNA is formed by transcription in eukaryotes. (5)

A
  1. Hydrogen bonds (between DNA bases) break;
  2. (Only) one DNA strand acts as a template;
  3. (Free) RNA nucleotides align by complementary base pairing;
  4. (In RNA) Uracil base pairs with adenine (on DNA)
    OR
    (In RNA) Uracil is used in place of thymine;
  5. RNA polymerase joins (adjacent RNA) nucleotides;
  6. (By) phosphodiester bonds (between adjacent nucleotides);
  7. Pre-mRNA is spliced (to form mRNA) OR
    Introns are removed (to form mRNA);
65
Q

Define ‘non-coding base sequences’ and describe where the non-coding multiple repeats are positioned in the genome.

A
  1. DNA that does not code for protein/polypeptides OR
    DNA that does not code for (sequences of) amino acids
    OR
    DNA that does not code for tRNA/rRNA;
  2. (Positioned) between genes;
66
Q

Describe how one amino acid is added to a polypeptide that is being formed at a
ribosome during translation.
[3 marks]

A
  1. tRNA brings specific amino acid (to ribosome);
  2. Anticodon (on tRNA) binds to codon (on mRNA);
  3. Amino acids join by condensation reaction (using ATP)
    OR
    Amino acids join to form a peptide bond (using ATP);
67
Q

Mutation can result in an increase in genetic variation within a species.

Describe and explain the other processes that result in increases in genetic variation
within a species.
[4 marks]

A
  1. Independent segregation of homologous Chromosomes/pairs;
  2. Crossing over between homologous chromosomes/pairs;
  3. Random fertilisation of gametes;
  4. (Produces) new combinations of alleles;
68
Q

Describe the structure of DNA and the structure of a chromosome.
[6 marks]

A
  1. Polymer of nucleotides;
  2. (Nucleotide) consists of deoxyribose, phosphate and an organic/nitrogenous base;
  3. Phosphodiester bonds (between nucleotides);
  4. DNA double helix held by H bonds
    OR
    2 strands held by H bonds;
  5. (Hydrogen bonds/pairing) between adenine,
    thymine and cytosine, guanine;
  6. DNA is associated with histones/proteins;
  7. (During mitosis/when visible) chromosome consists of two chromatids joined at a centromere;
69
Q

Multiple copies of the AMY1 gene is an adaptation to a high-starch diet. Suggest how this evolved through natural selection. (3)

A
  1. Mutation(s) produce extra copies of (AMY1) gene;
  2. Those with more copies / this adaptation/mutation reproduce / survive better on high starch diet;
  3. And pass on multiple copies / this adaptation/mutation (to offspring);
70
Q

Multiple copies of the AMY1 gene is an adaptation to a high-starch diet. Use your knowledge of protein synthesis and enzyme action to explain the
advantage of this adaptation. (3)

A
  1. More mRNA / more transcription; 2. More translation / enzyme;
  2. So reaction faster;
71
Q

Differences in the primary structure of haemoglobin molecules can provide evidence
of phylogenetic (evolutionary) relationships between species. Explain how.
[5 marks]

A
  1. Mutations change base / nucleotide (sequence);
  2. (Causing) change in amino acid sequence;
  3. Mutations build up over time;
  4. More mutations / more differences (in amino acid
    / base / nucleotide sequence / primary structure) between distantly related species;
    OR
    Few(er) mutations / differences (in amino acid / base / nucleotide sequence / primary structure) in closely related species;
  5. Distantly related species have earlier common ancestor;
    OR
    Closely related species have recent common ancestor;

A Level Biology (12 decks)

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