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Biology- Mrs Bell > Natural Selection > Flashcards

Natural Selection Flashcards

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1
Q

Similarities of prokaryotes and eukaryotes

A
  • Made of DNA nucleotides containing deoxyribose, a phosphate group and a nitrogenous base
  • Nucleotides are joined together by phosphodiester bonds to make a polymer chain
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2
Q

Differences of prokaryotes and eukaryotes

A

Eukaryotes~
- Longer
- Linear
- Associated with histones

Prokaryotes~
- Shorter
- Circular
- Associated with proteins

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3
Q

What is a gene?

A

A gene is a base sequence of DNA that code for:
1. The amino acid sequence of a polypeptide
2. A functional RNA

Every gene occupies a particular position on a chromosome, this is called the locus

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4
Q

3 features of the genetic code

A
  1. Degenerate
  2. Universal
  3. Non- overlapping
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5
Q

What does degenerate mean?

A

Coded for by one more triplet base

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6
Q

What does universal mean?

A

The same triplet of bases codes for the same amino acid in all organisms

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7
Q

What does non- overlapping mean?

A

Each base in a gene is only part of one of bases that codes for one amino acid. Therefore, each codon, or triplet of bases, is read as a discrete unit

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8
Q

What is an intron?

A

Introns are sections of DNA that do not code for polypeptides. They are found in only eukaryotic cells

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9
Q

What is an exon?

A

Exons are the sequence of DNA that do code for amino acids

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10
Q

What is a codon?

A

3 bases on mRNA that code for a specific amino acid

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11
Q

What is a start codon?

A

3 bases at the start of every gene that initiate translation

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12
Q

What is a stop codon?

A

3 bases at the end of every gene that cause ribosomes to detach and therefore stop translation

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13
Q

Difference between a genome and a proteome

A

Genome- is an organisms complete set of genes in a cell
Proteome- is the full range of proteins that a cell is able to produce
The proteome constantly changes depending on which proteins are currently needed

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14
Q

Features of mRNA

A
  • Short, single- stranded molecules found in cytoplasm and nucleus
  • It is made during transcription- it is copied from DNA and is therefore complementary to the DNA sequence
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15
Q

Features of tRNA

A
  • Each tRNA molecule has a sequence of 3 bases called an anticodon, they are complementary to codons on the mRNA molecule
  • tRNA is involved in translation. It carries the amino acids that are used to make proteins to the ribosomes. tRNA is a single polynucleotide strand that is folded into a clover shape
  • Hydrogen bonds between base pairs hold the shape
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16
Q

What is transcription?

A

Where one gene on the DNA is copied into mRNA

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17
Q

What is translation?

A

Where the mRNA joins with a ribosome, and corresponding tRNA molecules brings the specific amino acid and codon codes for amino acids

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18
Q

Transcription process

A
  1. The DNA helix unwinds to expose the bases to act as a template
  2. Only one chain of the DNA acts as a template
  3. This process is catalysed by DNA helicase
  4. DNA helicase breaks the hydrogen bonds between the bases
  5. Free mRNA nucleotides in the nucleus align opposite exposed complementary DNA bases
  6. The enzyme RNA polymerase joins together the RNA nucleotides to create a new RNA polymer chain. One entire gene is copied
  7. It then leaves the nucleus through the nuclear envelope pores
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19
Q

Pre-mRNA

A

After transcription, pre- mRNA is made, which is mRNA that still contains the introns. The introns are spliced out by a protein called a spliceosome. This leaves behind the exons
In prokaryotes, transcription directly creates mRNA, as prokaryotes do not contain introns in their DNA

20
Q

Translation process

A
  1. Once modified mRNA has left the nucleus it attaches to a ribosome in the cytoplasm
  2. The ribosome attaches at the start codon
  3. The tRNA molecule with the complementary anticodon to the start codon aligns opposite the mRNA, held in place by the ribosome
  4. The ribosome will move along one codon on the mRNA molecule to enable another complementary tRNA to attach to he next codon on the mRNA
  5. The 2 amino acids that have been delivered by the tRNA molecule are joined by a peptide bond. This is catalysed by an enzyme and requires ATP
  6. It continues until the ribosome reaches the stop codon at the end of the mRNA molecule. The stop codon does not code for an amino acid and therefore the ribosome detaches and translation ends
  7. The peptide chain will enter the Golgi body for folding and modification
21
Q

What is a mutation?

A

A change in the base sequence of the DNA, they are random. It can result in substitution and deletion

22
Q

What causes random mutations?

A
  • Mutagenic agents
  • High energy radiation
  • Chemicals
  • Ionising radiation
23
Q

What is non- disjunction?

A

When the chromosome or chromatids do not split equally during anaphase

24
Q

2 forms of non- disjunction

A
  1. Changes in whole sets of chromosomes (polyploidy)
  2. Changes in the number of individual chromosomes (aneuploidy)
25
Q

What does polyploidy mean?

A

Changes in whole sets of chromosomes occur when organisms have 3 or more sets of chromosomes rather than the usual 2.

26
Q

Process of polyploidy

A

Each homologous pair is doubled, due to DNA replication in interphase.
Non- disjunction in meiosis 1- all chromosomes fail to separate equally
Normal division in meiosis 2- chromatids separate equally
Chromosomes in 1 gamete

27
Q

What does aneuploidy mean?

A

Changes in the number of individual chromosomes

28
Q

Process of aneuploidy

A

Sometimes individual homologous pairs of chromosomes fail to separate during meiosis, This usually results in a gamete having one more or one fewer chromosome
A person with downs syndrome has 3 copies of chromosome 21

29
Q

What is meiosis?

A

2 nuclear divisions that creates 4 haploid genetically different haploid cells from a single parent cell

30
Q

Variation is meiosis

A
  • Independent segregation of homologous chromosomes
  • Crossing over between homologous chromosomes
31
Q

What is independent segregation

A

It is random which side of the equator the paternal and maternal chromosomes from each homologous pair lie. These are separated so one of each pair ends up in the daughter cell. This can be calculated using 2n

32
Q

What is crossing over?

A

When homologous pairs line up opposite each other at the equator in meiosis 1, parts of the chromatids can become twisted around each other. This puts tension of the chromatids, causing parts of the chromatid to break. The broken parts of the chromatid recombine with another chromatid. This results in new combinations of alleles

33
Q

Differences between meiosis and mitosis

A

Meiosis-
2 nuclear divisions
Haploid cell
Introduces genetic variation

Mitosis-
1 nuclear division
Diploid cells
Creates genetically identical cells

34
Q

What is genetic diversity?

A

The number of different alleles of genes in a population. Natural selection can only occur if there is genetic diversity within a population

35
Q

Natural selection

A

Natural selection is the process that leads to evolution in populations. Evolution is the change in allele frequency over many generations in a population. Natural selection results in species becoming better adapted to their environment, changes may be anatomical, behavioural or physiological

36
Q

Process of natural selection

A
  1. New alleles for a gene are created by random mutations
  2. If the new alleles increase the chances of the individual to survive in that environment, then they are more likely to survive and reproduce
  3. This reproduction passes on the advantageous allele to the next generation
  4. As a result, over many generations, the new allele increases in frequency in the population
37
Q

Directional selection

A

Occurs when there is a change in the environment

38
Q

Stabilising selection

A

Occurs when there is no change in the environment
Standard deviation decreases, as individuals with the extreme trait decrease

39
Q

Species and Taxonomy

A

2 organisms belong to the same species if they are able to produce fertile offspring
Courtship behaviour is essential for successful mating and for species recognition. This helps species to survive

40
Q

Courtship behaviour

A

A sequence of actions which is unique to each species. This is how animals identify members of their own species. They are performed by males only. They can include a sequence of dance moves, sounds, release of pheromones, display of colourful feathers or fighting. Females observe the ritual and decide whether they want to mate

41
Q

Importance of courtship

A
  • Enables them to recognise their own species and opposite sex
  • Synchronises mating behaviour- indicates sexually mature and in season
42
Q

Courtship in species recognition

A

The more similar a courtship sequence is between different species, the most closely related a species are

43
Q

Phylogenetic classification

A

Arranges species into 2 groups according to their evolutionary origins and relationships
It tells us how closely related species are and how recent their shared common ancestors are

44
Q

What is a hierarchy?

A

Smaller groups arranged within larger groups, there is no overlap between groups

45
Q

Order of the hierarchy

A

Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species

46
Q

Binomial system

A

Each species is universally identified using the binomial (2 name)
First name is genus, second name is species e.g. Homo sapiens

Biology- Mrs Bell (4 decks)

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