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Biology > M4 DNA > Flashcards

M4 DNA Flashcards

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1
Q

Describe the length, shape, chromosome formation and protein association of DNA in:

  • prokaryotes
  • eukaryotes
  • chloroplasts and mitochondria
A

PROKARYOTES
- Short, circular, does not form chromosomes and not associated with proteins

EUKARYOTES
- Long, linear, forms chromosomes and IS associated with proteins.

CHLOROPLASTS AND MITOCHONDRIA
- Very Short, circular, does not form chromosomes and is not associated with protein molecules.

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2
Q

What are chromosomes? Their structure? How are they formed?

A

Threads composed of DNA composed of two identical chromatids held together at the centromere.

DNA molecules combine with histone proteins. The DNA histone complex is coiled. Coil folds to form loops. Loops coil and pack together to form a chromosome.

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3
Q

What is an allele?
Different alleles have different _______ of ____ so produce different polypeptides.

A

A version of a gene

sequences
bases

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4
Q

What is a gene?

A

A section of DNA that contains the information for making a polypeptide.

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5
Q

DNA codes for the ______ sequence of amino acids in a polypeptide. There are __ amino acids that are commonly used in proteins.

A

primary
20

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6
Q

If three bases coded for an amino acid, how many amino acids could be coded for?

A

4^3 = 64

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7
Q

A set of 3 bases in DNA is known as a _____. While in mRNA it’s known as a _____. And in tRNA it’s known as ______.

A

Triplet
Codon
Anticodon

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8
Q

Why is DNA converted to mRNA before protein synthesis?

A

Because it is small enough to leave the nucleus and enter the cytoplasm to be used by tRNA.

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9
Q

The genetic code is known as degenerate. What does this mean?

A

Most amino acids are coded for by more than one triplet.

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10
Q

What is always the first codon in the mRNA sequence? What amino acid does it code for?

A

AUG - methionine

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11
Q

What are stop sequences?

A

Codons that do not code for amino acids - marking the end of the polypeptide chain.

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12
Q

Why is genetic code universal?

Why is it non-overlapping?

A

Because the same codon codes for the same amino acid in all organisms.

Non-overlapping as each base in the sequence is part of only one codon.

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13
Q

What is Transcription and Translation?

A

Transcription - mRNA formed from DNA

Translation - tRNA uses mRNA to form polypeptide

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14
Q

Compare transcription in eukaryotes to prokaryotes.

A

EUKARYOTES

  • mRNA must be processed.
  • mRNA exits nucleus.
  • Transcription finishes before translation starts.

PROKARYOTES

  • no introns so no processing.
  • no nucleus present
  • translation starts before transcription finishes.
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15
Q

What are introns and exons?

A

Introns = non-coding sequences (made up of long sequences of multiple repeat bases).

Exons = coding sequences.

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16
Q

Describe the process of transcription.

A

An enzyme unwinds a section of DNA, exposing the nucleotide bases on the template strand. Exposed bases pair with complementary nucleotides present in the nucleus.

Enzyme RNA polymerase moves along the strand joining RNA nucleotides together. The DNA strand behind it reforms (so only around 12 bases pairs on DNA are exposed at once). When RNA polymerase reaches a stop sequence of bases it detaches and the pre-mRNA molecule is complete.

Pre-mRNA is processed to remove introns and leaves the nucleus.

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17
Q

What are the names of the 3 phases of translation?

A

Initiation, Elongation, Termination

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18
Q

Describe the process of Translation - Initiation

A

Initiation:
Ribosome attaches to the start codon AUG at one end of the mRNA molecule.
The tRNA molecule with complementary anticodon moves to the ribosome and binds with the codon on the mRNA, carrying the amino acid methionine.

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19
Q

Describe the process of Translation - Elongation

A

Elongation:
The next tRNA with the complementary anticodon enters the ribosome and a peptide bond is formed between the two amino acids. An enzyme is required as well as ATP to form this bond.
The ribosome translocates along the mRNA sequence allowing a new tRNA to enter the ribosome. The empty tRNA is released from the ribosome to be recycled by addition of another amino acid (binding of this amino acid requires ATP).
This is a RAPID process.

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20
Q

Describe the process of Translation - Termination

A

The synthesis of the polypeptide continues until a ribosome reaches a stop codon. The ribosome, mRNA and last tRNA molecule all separate and the polypeptide chain is terminated.

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21
Q

What is the genome?

A

The complete set of genes in a cell including those in the mitochondria and chloroplasts.

22
Q

What is the proteome?

A

The full range of proteins produced by the genome.

23
Q

What was the experiment that Hershey and Chase conducted to prove that DNA not protein was the genetic material?

A

In two parallel experiments, Bacteriophages (virus) containing radioactive labels (32P or 35S) were allowed to infect bacteria. The 32P involved itself in the viral DNA and 35S involved itself in the viral protein coat. Following infection the cultures were agitated in a blender to detach viruses from the bacterial cells and then centrifuged to form a pellet and supernatant which were then screened for radioactivity.

Supernatant contained viruses. pellet contained bacterial cells.

RESULTS
32P found in Pellet only and 35S found in supernatant only. Suggesting that DNA injected into cells while protein coat remained outside of cells. So DNA concluded to be the genetic material NOT the protein.

24
Q

What is a mutation?

A

Any change in the quantity or base sequence of the DNA of an organism.

25
Q

What is a gene mutation?

A

Any change in the nucleotide bases or the sequence of bases.

26
Q

What is a chromosome mutation?

A

Any change to the quantity of DNA.

27
Q

When does a substitution mutation occur? What is it’s effect on the protein?

A

When a nucleotide is replaced by another nucleotide with a different base.

Leads to no change in amino acid or a different amino acid - may cause polypeptide to have reduced or no function. This is because a change in amino acid may change bonds formed, changing tertiary structure. Sometimes subsitution forms a STOP sequence, shortening the polypeptide chain.

28
Q

When does a deletion mutation occur? What are the effects?

A

When a nucleotide is lost from the DNA sequence.

Causes a shift in the reading frame of the DNA and can change all of the amino acids in the polypeptide.

29
Q

How do mutations occur?

A

Spontaneously as the result of errors in DNA replication.

30
Q

What are mutagenic agents?

A

Things that can increase the rate of mutations by causing damage to DNA
- e.g. ultraviolet light and smoking

31
Q

What is the difference between diploid and haploid cells?

A

Diploid cells have homologous pairs of chromosomes (2 of each type of chromosome) - 2n.

Haploid cells DO NOT have homologous pairs of chromosomes - n.

32
Q

Meiosis is a type of cell division used in the production of ______. It consits of __ divisions and __ gametes are produced. Each gamete is ______. During fertilisation the ______ state is restored.

A

gametes
2
4
haploid
diploid

33
Q

In humans, each homologous pair is split into one ________ and one _______ chromosome. In meiosis 1 these pairs separate completely _________ into each daughter cell. This is called _______ __________ and provides a huge variety of different combinations of chromosomes in the gametes, leading to _______ _________.

A

maternal
paternal
randomly
Independent Segregation
Genetic Variation

34
Q

What is random fertilisation?

A

The chance of a specific sperm fusing with a specific egg.

It further increases the genetic variation by providing a huge variety of new combinations of chromosomes.

35
Q

What happens in Meiosis 1?

A

Prophase 1:
Homologous pairs come together. Non-sister chromatids cross over (leading to new combination of alleles).

Metaphase and Anaphase 1:
Homologous pairs line up along the equator of the cell. Spindle fibres attach to each centromere and pulls one of each homologous chromosome to each pole. Crossed over sections are exchanged.

Telophase
Cytokenesis

36
Q

What happens in Meiosis 2?

A

Further division of cells - one chromatid from each chromosome randomly pulled to each pole forming gametes which are all genetically different.

37
Q

Compare mitosis and meiosis.

A

MITOSIS
Froms genetically identical cells.
Produces 2 daughter cells that have same number of chromosomes as parent.
One division.
No crossing over.
Froms diploid cells.

MEIOSIS
Froms genetically different cells.
Produces 4 daughter cells which have half the number of chromosomes as parent cell.
2 divisions
Crossing over in Meiosis 1 leads to new combinations of alleles.
Forms haploid cells.

38
Q

What causes changes in chromosome numbers?

A

Non-disjunction events - failure to separate.

On rare occasions chromosomes do not seperate correctly during anaphase 1 or 2 of meiosis, resulting in gametes that have too many or too few chromosomes.

39
Q

What are the effects of having a different number of chromosomes caused by mutations?

A

Having more copies of a particular gene means that more proteins produced.
Having less copies means that less proteins produced.

Chromosome mutations can result in complex syndromes with varying characteristics.

40
Q

When does polyploidy occur?

A

When organisms have 3 or more complete sets of chromosomes rather than 2.

This occurs mostly in plants and results in organisms that are 3n, 4n etc.

41
Q

How can you tell if meiosis or mitosis has occured in an exam question?

A

Meiosis halves chromosome number while mitosis retains chromosome number - whether it is 2n or n.

42
Q

Compare gene and chromosome mutation.

A

GENE MUTATIONS

  • Change in nucleotide sequence in a particular gene.
  • Affects only one gene and only one copy of the gene.
  • One protein may have reduced/no function.

CHROMOSOME MUTATIONS

  • Involves change in the number or structure of chromosomes.
  • Affects many genes and changes the number of copies of many genes.
  • Keeps function but more or less proteins may be produced.
43
Q

What are the safety precautions/asepctic techniques for the practical that investigates the growth of bacteria in the presence of different antimicrobial substances?

A
  • Incubate no higher than 30 degrees to discourage growth of human pathogens.
  • Do not tape all the way around the petri dish to prevent anaerobic conditions for harmful pathogen growth.
  • Work near a bunsen flame so hot rising air moves microbes away from your culture.
  • Steralise inoculating loop/spreader and neck of glass container with a bunsen flame before and after using.
  • Steralise glasswear before and after using an autoclave.
44
Q

What is genetic diversity? Why is it beneficial?

A

The total number of different alleles in a population.

Increases chances of survival of the population through the process of natural selection if environment changes.

45
Q

What increases genetic diversity?

A

Mutation which form new alleles and migration of individuals from different populations.

46
Q

What is allele frequency?

A

A measure of how common a partciular allele is in a population.

Allele frequencies change over time due to natural selection.

47
Q

Describe the process of natural selection.

A

1) New allele rises through mutation.
2) Mutation may be beneficial to survival in a certain environment.
3) Species tend to over-produce offspring, leading to competition for resources.
4) If the new allele increases the chance of survival and reproduction this allele will be passed on to the offspring - called reproductive success.
5) Allele frequency increases with each successive generation.
6) Over time leads to evolution.

48
Q

What are the 3 types of adaptations that can occur?

A

Anatomical, Physiological and Behavioural

49
Q

What is directional selection.

A

The mean (highest poit) shifts.

Selection against one exetreme and slection for another extreme.

50
Q

What is Stabalising Selection?

A

Mean is selected for.

51
Q
A

Biology (17 decks)

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