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A- Level Biology > Unit 4 > Flashcards

Unit 4 Flashcards

1
Q

Describe the role of DNA.

A

Carries genetic information, determines
our inherited characteristics.

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2
Q

Describe the structure of RNA.
func=Transfers genetic information from DNA to ribosomes for protein synthesis.

A

Made up of a ribose sugar, a phosphate
group, and one of four organic bases (A,C,G,U).
It is single stranded.

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3
Q

How is DNA in eukaryotic cells different from in prokaryotic cells?

A

● Eukaryotic cells=
-found in nucleus
-long and linear
-Associated with histone proteins to form chromosomes.

Mitochondria and chloroplasts
contain prokaryotic-like DNA.
● Prokaryotic cells= short and circular.
Not associated with proteins.

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4
Q

What is the genetic code?

A

Order of bases on DNA
Consists of codons (triplets of bases that code for a particular amino acid

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5
Q

Identify features of the genetic code 3

A

● Non-overlapping= each triplet is only read once.
● Degenerate= more than one triplet (codon) codes for the
same amino acid
● Universal= same bases and sequences used by all species

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6
Q

What is a gene? 3

A

A sequence of bases on a DNA molecule
- that codes for a specific sequence of amino acids to make a polypeptide.
Can also code for functional RNA.

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7
Q

What is a locus?

A

The fixed position on a DNA molecule occupied by a gene

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8
Q

What is an allele?

A

Different versions of the same gene, found at the same locus on a
chromosome

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9
Q

What are exons and introns?
(introns, between exons within genes)

A

Exons= regions of DNA that code for amino acid sequences. Separated by
one or more introns.

Introns= regions of DNA that do not code for anything.

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10
Q

What is the genome?

A

The complete set of genetic information contained in the cells of an organism

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11
Q

What is the proteome?

A

The complete set of proteins that can be produced by a cell.

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12
Q

Describe the structure of messenger RNA (mRNA) 4

A

-long
-uracil instead of thymine
-single strand
-Its base sequence is complementary to the DNA it was
transcribed from

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13
Q

Suggest advantages of using mRNA rather than DNA for translation. 3

A

● shorter & contains uracil = breaks down quickly so no excess polypeptide forms
● single-stranded & linear = ribosome moves along strand & tRNA binds to exposed bases
● contains no introns

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14
Q

Describe the structure of transfer RNA
(tRNA).

A

-A single strand of around 80 nucleotides
- folded over into a clover leaf shape
-one end is an anti-codon
-on the opposite end is an amino acid binding site

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15
Q

Outline the process of transcription happens in the nucleus 6

the production of mRNA from DNA
RNA polymerase in joining mRNA nucleotides.

A

-Hydrogen bonds between DNA bases break
-Only one DNA strand act as a template
-Free adjacent RNA nucleotides align by complementary base pairing
-In RNA, Uracil is used instead of thymine
-RNA polymerase joins RNA nucleotides together by phosphodiester bonds from pre-mRNA
-pre-mRNA is spliced to remove introns, forming mRNA

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16
Q

What happens to mRNA after transcription (copy)?2

A

-In eukaryotic cells, pre-mRNA must be spliced to remove introns, leaving only the coding regions.
-Then it moves out of the nucleus and attaches to a ribosome

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17
Q

Outline the process of translation. 7
-happens in the cytoplasm on ribosomes
-proteins produced

A

-mRNA attaches to ribosomes
-tRNA anticodons bind to complementary mRNA codons
-tRNA brings a specific amino acid.
-Amino acids join by peptide bonds.
-Amino acids join together with the use of ATP
-tRNA released after amino acid joined to the polypeptide
-The ribosome moves along the mRNA to form the polypeptide;

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18
Q

What is a mutation

A

An alteration to the DNA base sequence.
Often arise spontaneously during DNA
replication.

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19
Q

Why might a mutation not lead to change in the amino acid sequence?

A

● Genetic code is degenerate so
mutation may end up coding for same
amino acid as the original triplet.
● Mutation may occur in intron.

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20
Q

What is a substitution mutation?
-genetic code degenerate so not all substitions result in a change in the primary structure of a polypeptide chain

A

When a nucleotide in the DNA sequence is replaced by another. This is more likely to be a quiet mutation, meaning no change occurs in the amino acid sequence

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21
Q

What is a deletion mutation

A
  • nucleotide in the DNA sequence
    is lost.
    -leads to a frame shift
    -entire amino acid sequence will be different.
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22
Q

What is a mutagenic agent? Give
examples of this 2

A

-Factors that increase the rate of gene
mutation.
-X-rays, UV light, gamma rays,
certain chemicals e.g. in alcohol and
tobacco.

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23
Q

What is chromosome non-disjunction?

A

chromosomes/ chromatids fail to separate correctly in meiosis resulting in gametes with one more or less chromosome than normal

-in anaphase 1 /meiosis homologous pairs fail to separate and are not pulled to opposite poles

-in anaphase 2 sister chromatids fail to separate and are not pulled to opposite poles

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24
Q

What is meiosis?2

A

-A form of cell division
-produces four
genetically different haploid cells (cells with half the number of chromosomes found in the parent cell) known as gametes.

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25
How does meiosis differ from mitosis?2
● Meiosis produces four genetically different cells with half the number of chromosomes as the parent cells. ● Mitosis produces two genetically identical cells with the same number of chromosomes as the parent cells
26
What happens during meiosis Ⅰ?3
1. Homologous chromosomes pair to form bivalents. 2. Crossing over (exchange of sections of genetic material) occurs at chiasmata. 3. Cell divides into two. Homologous chromosomes separate randomly. Each cell contains either maternal or paternal copy.
27
What happens during meiosis Ⅱ?2
1. Independent segregation of sister chromatids. 2. Each cell divides again, producing 4 haploid cells.
28
In which two ways does meiosis produce genetic variation? 2* *= how many homologous pairs of chromosomes 2=homologous pairs
1. Crossing over during meiosis Ⅰ 2. Independent assortment (random segregation) of homologous chromosomes & sister chromatids Result in new combinations of alleles.
29
crossing over of chromosomes 3
-homologous pairs of chromosomes associate to form bivalents -chiasma forms -equal lengths of non-sister chromatids are exchanged producing new combination of alleles
30
ethical and economical argument for biodiversity
eth -Prevent extinction / loss of populations / reduction in populations / loss of habitats / save organisms for future generations econ-medical / pharmaceutical uses; commercial products, tourism; agriculture; saving local forest communities
31
Define population
All the organisms of a particular species that live in the same place
32
Define genetic diversity
the number of different alleles of genes in a population.
33
What advantage does a high genetic diversity provide?
Ability to adapt to a change in environment; allows natural selection to occur.
33
What advantage does a high genetic diversity provide?
Ability to adapt to a change in environment; allows natural selection to occur.
34
Explain how natural selection results in development of new characteristics.
● Random mutations result in new alleles. ● Some alleles provide an advantage, making an individual more likely to survive and reproduce. ● Their offspring receive the new allele, and frequency continues to increase over many generations
35
What is directional selection?
Occurs when environmental conditions change. Individuals with phenotypes suited to the new conditions will survive and pass on their genes. Over time the mean of the population will move towards these characteristics
36
Give an example of directional selection.
Antibiotic resistance. Bacteria with a mutation allowing them to survive in the presence of antibiotics will reproduce. Therefore frequency of this allele will increase and the population will shift to have greater antibiotic resistance.
37
What is stabilising selection?
Occurs when environmental conditions stay the same. Individuals closest to the mean are favoured, and any new characteristics are selected against. Results in low diversity
38
Give an example of stabilising selection.
Birth weight; babies that weigh around 3kg are more likely to survive than those at lower or higher weights.
39
Define a niche
The role of a species within its environment. Species sharing the same niche will compete with each other
40
What are the three types of adaptation? Give examples of each
● Anatomical (changes to body structure) e.g. oily fur. ● Physiological (changes to bodily processes) e.g. venom production. ● Behavioural (changes to actions) e.g. hibernation
41
Define species.
A group of organisms that can interbreed to produce fertile offspring
42
What are the advantages of courtship behaviour?
Individuals can recognise sexually mature members of their own species of the opposite sex, synchronise mating, form a pair bond, and successfully breed
43
Define classification
The process of arranging organisms into groups.
44
Name the eight groups in the classification hierarchy, from largest to smallest.
domain → kingdom → phylum → class → order → family → genus → species
45
What system is used to give species a universal name?
Binomial naming system.
46
What are the two components to a binomial name?
Generic name= the genus the organism belongs to. Two closely related species will share the same genus. Specific name= the species the organism belongs to.
47
How are binomial names handwritten?
The first letter of the generic name should be capitalised, with the rest in lowercase. The whole name should be underlined
48
What is phylogenetic classification?
The process of arranging organisms into groups based on their evolutionary origins and relationships
48
How can we clarify evolutionary relationships between organisms?
Analyse their molecular differences. Advances in immunology/genome sequencing provide clear pictures of how related two organisms are.
49
Explain hierarchical classification.
● groups within groups ● no overlap between group
50
Define community.
All the different species that live in one area and interact with each other
50
What is biodiversity?
The variety of living organisms. It can be measured in terms of species diversity (number of species in a community), ecosystem diversity (range of different habitats) and genetic diversity
51
How do you calculate index of diversity (d)?
d= N(N-1) ---------- Σ n(n-1) N= total number of organisms of all species. n= total number of Σ = sum of organisms of each species.
52
What impact does agriculture (farming) have on species diversity?
decreases species richness ● farmland is typically used for only 1 species (monoculture) ● use of pesticides/ herbicides
53
What impact does agriculture (farming) have on genetic diversity?
decreases ● farmers select for certain characteristics, which reduces number of different alleles in the population
54
How can biodiversity be increased in areas of agriculture?
1. Use hedgerows instead of fences. 2. Grow different crops in the same area, or rotate crops around after a season. 3. Limit use of pesticides and herbicides
55
Name four ways we can measure genetic diversity
1. Frequency of observable characteristics. 2. Base sequence of DNA. 3. Base sequence of mRNA. 4. Amino acid sequence.
56
What is meant by interspecific and intraspecific variation
Interspecific= differences between individuals of different species. Intraspecific= differences between individuals of the same species
56
What is meant by gene technology?
Sampling DNA or mRNA in order to read and compare the base sequence of organisms. Alternatively the amino acid sequence can be studied as this will also provide information on the organism’s mRNA and DNA sequences.
57
Why do scientists prefer to use gene technology instead of observation?
Simply inferring DNA differences by observing an organism’s characteristics is not reliable; the characteristics could be coded for by more than one gene, or could be influenced by the environment
58
What is sampling?
Selecting a group of individuals to measure that will represent the whole target population.
59
How can a random sample be achieved?
Create a grid for your sample area, and then randomly generate coordinates where a quadrat or transect can be placed. Repeat until required sample size is reached
60
what is species richness
(A measure of) the number of (different) species in a community
61
non coding bases sequences
sequence of dna that doesn't code of a amino acid found within genes as introns
62

A- Level Biology (9 decks)

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