Topic 8: DNA, Genes, Protein Synthesis Flashcards

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1
Q

What is a gene

A

A gene is a base sequence of DNA that codes for:
- the amino acid sequence of a polypeptide
- a functional RNA

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2
Q

What do you call the fixed position of the gene on a DNA molecule

A

Locus

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3
Q

Where is DNA found

A

Mostly in nucleus
(also in mitochondria as mitochondial dna)

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4
Q

What are the 4 bases of DNA

A
  • Adenine
  • Thymine
  • Cytosine
  • Guanine
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5
Q

What is a codon

A

A sequence of three bases that codes for a single amino acid

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6
Q

How many amino acids are coded for in protein synthesis

A

20 amino acids

(because some have multiple codes)

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7
Q

What does it meanby the genetic code being degenerate

A

several code words have the same meaning (amino acid)

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8
Q

What are stop codes

A

When the codon does not code for an amino acid, but for the ribosome to stop the polypepetide chain

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9
Q

What is always the start codon

A

Methionine
(AUG)

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10
Q

What does it mean by the code is non-overlapping

A

Each base is only read once, and the triplets are read in the same direction

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11
Q

What does it mean by the code being universal

A

The genetic code is the same in almost every living being, with a few specific exceptions.

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12
Q

What do you call a sequence that does not code for an amino acid

A

Introns

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13
Q

What do you call a sequence that codes for an amino acid

A

Exons

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14
Q

What happens to the introns

A

They are removed by splicing before the final mRNA reach the ribosomes.

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15
Q

What do you call the proteins associated with DNS

A

Histones

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16
Q

What forms a chromosone

A

DNA molecule and its associated proteins (histones)

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17
Q

When the cell is not dividing, what are the chromosones like?

A
  • not visible
  • uncoiled
  • loosely found throughout nucleus
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18
Q

How do chromosones appear at the start of cell division

A

Two threads joined at a central point (centromere).

19
Q

What does each chromosone consist of

A
  • two identical DNA molecules (chromatids)
  • held together by proteins called histones.
20
Q

How are chromatids of a chromosone produced?

A
  • The DNA helix is wound tightly around histones acting as packaging proteins, forming a nucleosome.
  • A series of nucleososmes looks like beads on a string in an electron micrograph.
  • The string of nucleosomes then loops and coils into the *30nm fibre. *
  • The 30nm fibre folds up further into a 300nm wide supercoil.
  • This then produce the chromatid of a chromosome.
21
Q

What is the advantage of DNA coiling?

A

A lot of DNA can be packed into the chromosome, with each chromosome consisting of a single, very long strand of DNA.

22
Q

What is a homologous pair

A
  • two copies of each chromosome
  • always carry same genes but may have different alleles of the genes.
23
Q

During meiosis, what happens to the number of chromosones

A

number of chromosomes is halved and this is controlled so that each daughter cell end up with one chromosome from each homologous pair.

24
Q

What is an allele

A

One of a number of different forms of the same gene.

25
Q

How do you inherit alleles (sexual organisms)

A
  • One allele from mum
  • One allele from dad

(Can be different or the same)

26
Q

What happens if the two inherited alleles are different

A

The result will be two different polypeptides being expressed.

27
Q

What happens to the allele if there is a mutation

A

A new allele will form, producing a different polypeptide

28
Q

What is an organisms genome

A

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

29
Q

What is the proteome

A

The full range of proteins produced by the genome

30
Q

Where does the synthesis of proteins happen?

A

In the cytoplasm
(in the ribosomes)

31
Q

What is the function of mRNA

A

To transfer information from the nucleus to the ribosome

32
Q

Name four differences between RNA and DNA

A
  1. RNA has the sugar ribose instead of deoxyribose
  2. RNA has the base uracil instead of thymine
  3. RNA is usually single stranded, but can fold into 3-dimentional structures, like proteins.
  4. RNA is usually shorter than DNA
33
Q

How long is mRNA

A

One gene long

34
Q

How does the codon bind to a tRNA molecule

A

Using the anticodon of the tRNA

35
Q

What are some features of a tRNA molecule

A
  • One end has the amino acid bidning site
  • One end has the anticodon which is a triplet code to bind to the codon
  • Clover shaped
36
Q

How are the amino acids attatched to the tRNA molecule

A

By specific **aminoacyl tRNA synthase enzymes. **

37
Q

What two things form ribosomes

A
  • RNA
  • other Protiens
38
Q

What do ribosomes do

A
  • Site of mRNA translation
  • Site of protein synthesis
39
Q

What are ribosomes made up of

A

2 sub units
(Large and Small)

40
Q

Where are ribosomes assembled

A

Assembled in the nucleolus of the nucleus and exported into the cytoplasm.

41
Q

What do the different ribosomes make protiens for

A
  • Ribosomes in the cytoplasm make protiens for use in the cell
  • Ribosomes made in the RER make protiens for export
42
Q

Where is tRNA made

A

In the nucleus

43
Q
A