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Section 4 Flashcards

1
Q

Define homologous chromosome

A

Chromosomes which have the same gene at the same loci but may have different alleles.

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2
Q

Define gene

A

sequence of DNA bases that codes for a specific polypeptide chain

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3
Q

What is a triplet code

A

Three bases which code for a particular amino acid

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4
Q

What is meant by a degenerate genetic code

A

most amino acids are coded for by more than one triplet

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5
Q

What is non-overlapping

A

DNA is read in triplets and each base is read once.

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6
Q

What is meant by universal

A

The same triplet codes for the same amino acids in all organisms.

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7
Q

Describe the DNA in prokaryotic cells

A

They are short, circular and not associated with proteins.

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8
Q

Describe DNA in eukaryotic cells and where is it found

A

In the nucleus, DNA is very long, linear and associated with proteins (histones). They form chromosomes with proteins.

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9
Q

What are introns and exons?

A

Introns: DNA base sequence within a gene not coding for a sequence of amino acids

Exons: DNA base sequence within a gene coding for a sequence of amino acids

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10
Q

What’s the structure of mRNA

A

Single stranded
Ribose sugar
Uracil
Linear shape
Shorter than DNA
No hydrogen bonds
Codon
No amino acid binding site

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11
Q

Describe the structure of tRNA

A

It is very small (80 nucleotides) folded into clover leaf shape.
The extended end carries an amino acid.
The opposite end there are 3 unpaired bases forming an anticodon.

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12
Q

Define the genome

A

The complete set of genes in a cell

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13
Q

Define the proteome

A

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

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14
Q

Describe the process of transcription as being the first stage of protein synthesis

A

DNA strands separate breaking hydrogen bonds and produces DNA template strand. This template is used to make a complementary strand of mRNA. Free DNA nucleotides pair with their complementary bases via hydrogen bonds. The enzyme RNA polymerase moves along template strand and joins the nucleotides via phosphodiester bonds. Pre-mRNA is made which includes both exons and introns. Introns are cut out leaving exons and these are spliced together. mRNA then diffuses out of a nuclear pore.

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15
Q

What are the differences in protein synthesis in prokaryotic and eukaryotic cells.

A

Prokaryotic DNA doesn’t contain introns so splicing isn’t necessary.

Prokaryotic cells don’t have a nucleus so protein synthesis happens in the cytoplasm.

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16
Q

Describe translation as the second part of protein synthesis

A

mRNA attaches to a ribosome via the start codon. A tRNA molecules with a complementary anticodon pairs with mRNA codon via hydrogen bonds and the tRNA moecules carries it’s specific amino acid. Another tRNA molecule binds to the second mRNA . The two amino acids form a peptide bond with the help of ATP. The ribosome moves along the mRNA.

This process carries on until a STOP codon is reached and the polypeptide chain is complete.

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17
Q

Name 3 purposes of mitosis

A

Growth of multicellular organisms
Replacement of cells
Asexual reproduction

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18
Q

Name the 3 purposes of meiosis

A

Increasing genetic variation
Produces haploid cells
Chromosome number stays constant

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19
Q

Are maternal and paternal chromosomes genetically identical and explain why

A

They have different alleles so they have a different base sequence

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20
Q

Name the two nuclear divisions during meiosis

A

Meiosis 1
Meiosis 2

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21
Q

Describe what happens in meiosis 1

A

Homologous chromosomes pair up and their chromatids wrap around each-other. They then separate and produce haploid cells.

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22
Q

What happens in meiosis 2

A

The sister chromatids separate and produce haploid cells (gametes). Each of the cells contain a single chromosome from each original homologous pair.

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23
Q

What are the two methods in producing genetic variation?

A

Recombination by crossing over.

Independent segregation of homologous chromosomes.

24
Q

Describe the method of recombination by crossing over.

A

In meiosis one, homologous chromosomes pair up and form bivalents.
Non sister chromatids wrap around each-other so cross over at the chiasmata.
The broken off portions of non sister chromatids recombine with the other chromatid in the process of recombination.
This produces a new combination of alleles.

25
Describe independent segregation of homologous chromosomes.
In meiosis one, bivalents are formed. How they line up is random. The different combinations of maternal and paternal chromosomes line up is a matter of chance.
26
What are the two forms of change in structure of whole chromosomes.
Changes in whole sets of chromosomes- polyploidy (3 or more sets of chromosomes) Changes in the number of individual chromosomes- they fail to separate during meiosis and this is called non-disjunction.
27
Compare the processes of mitosis and meiosis
- mitosis involves one division whereas meiosis involves two - mitosis has diploid parent cells and produces diploid daughter cells whereas meiosis has diploid parents and haploid daughter cells - homologous chromosomes are not separated in mitosis whereas they are in meiosis - recombination and independent segregation doesn’t happen in mitosis whereas it does in meiosis
28
Describe the process of meiosis
In meiosis one, homologous chromosomes pair and form bivalents. Non sister chromatids cross over, break off and recombined exchanging alleles at the chiasmata creating new combinations of alleles. Each pair of homologous chromosomes line up independently and independent segregation occurs. Each homologous chromosome is pulled to opposite poles of the cells via spindle fibres attached to the centromere. In meiosis 2, sister chromatids are pulled to opposite sides of the cells and this produces 4 genetically different daughter cells.
29
Compare and contrast the DNA in eukaryotic cells with the DNA in prokaryotic cells
Both consist of nucleotides containing a phosphate, deoxyribose sugar and a base. Both have nucleotides held via phosphodiester bonds. Eukaryotic DNA is much longer. Eukaryotic DNA is linear but prokaryotic is circular. Eukaryotic DNA contains introns whereas prokaryotic DNA does not.
30
Explain how a gene codes for a protein
Base sequence on DNA determines the sequence of amino acids so the proteins primary structure. This happens by determining the base sequence on the mRNA and three of the bases code for an amino acid.
31
Define non-overlapping
Each base is part of only one triplet
32
Explain the difference in how mRNA is produced in prokaryotic compared to eukaryotic.
DNA in eukaryotic has non-coding introns within the gene but prokaryotic does not. Eukaryotic cells pre-mrna is produced containing introns which are then removed by splicing. But in prokaryotes splicing is not necessary.
33
Compare and contrast structures of mRNA and tRNA
Both are polymers of nucleotides. mRNA is linear whereas tRNA is a clover leaf shape. mRNA has codons whereas tRNA has anticodons. mRNA does not have an amino acid binding site whereas tRNA does.
34
Explain how a change in DNA base sequence for a protein may result in a change of structure of a protein and how this could affect its activity if it was an enzyme.
Mutation changes the DNA base sequence. Therefore the base sequence of mRNA changes and codons change. This causes a change in amino acid sequence so the primary structure of the protein changes. This causes tertiary bonds to change (hydrogen, ionic and disulphide) so changes the overall tertiary structure. The enzyme active site shape will change so substrate no longer binds and forms and no longer forms an enzyme substrate complex.
35
Define gene mutation
Change in DNA base sequence and results in the formation of a new allele.
36
Explain how a mutation might have no affect on an individual.
Genetic code is degenerate so amino acid might not change.
37
Explain how antibiotic resistance could become wide spread in a bacterial population
Frequent use of antibiotic creates selection pressure. Random mutation creates a new allele which is resistant to the antibiotic in some bacteria. These bacteria which are resistant have a selective advantage and survive so reproduce and pass on this resistant allele. Allele frequency increases in the new generations.
38
Define species
A species is a group of similar organisms which can reproduce sexually to produce fertile offspring.
39
Define phylogenetic group
Grouped according to evolutionary links or common ancestors
40
Explain hierachy
Groups within groups and no overlap between these groups.
41
Explain ways in which biologists use to classify organisms into groups.
Hierarchical systems: Large groups divided into smaller groups with no overlap Members have common DNA features and these reflect on evolutionary history and it enables the formation of a pair bond.
42
Name the taxonomic groups in order
Domain Kingdom Phylum Class Order Family genus species
43
Which courtship behaviours increases the probability of successful mating
It attracts recognition of the same species. Indicates sexual maturity Stimulates the release of gametes.
44
Define species richness
number of different species in a community
45
Define index of diversity
The number of different species and the number of different individuals of each species within any one community.
46
Define genetic diversity
The total number of different alleles in a population of one species
47
How does deforestation affect species diversity
Loss of plant species. Fewer different food sources. Fewer different habitats. Reduces number of different species in the habitat.
48
How does monoculture affect species diversity
Fewer plant species Fewer different types of food sources Reduces number of different species in the habitat
49
Explain subsitution mutations and when do mutations occur
Mutations occur randomly during DNA repilaction Subsitution mutations may not cause a change due to the possibility of the same codon so it still codes for the same amino acid. This is degenerate.
50
What happens during deletion mutation
Deletion mutation causes a base to be deleted from the sequence so this causes a frame shift of bases to the left which means the codon sequence has now changed which is harmful for the amino acids as they will no longer have the correct codon to attach to.
51
What are chromosome mutations and what are they caused by
Changes in number of chromosomes in a cell and can happen spontaneously by non disjunction.
52
What is non disjunction
When the chromosomes or chromatids don’t separate equally during anaphase
53
What are the two forms of non disjunction
Polyploidy- changes in whole sets of chromosomes Changes in the number of individual chromosomes
54
Describe how natural selection occurs
Random mutations causes new alleles for a gene in the population. This new allele gives the individual a selective advantage and they will be able to survive better and reproduce successfully passing on their allele to their offspring. Over many generations the allele frequency increases.
55
Describe directional selection
One of the extremes are selected for. And this occurs when there is a change in environment.
56
Describe stabilising selection
The average individualshas selective advantage. No change in environment. Both extremes selected against. Standard deviation decreases.

Biology alevel (10 decks)

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