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Biology > 4. DNA, Genes & Chromosomes > Flashcards

4. DNA, Genes & Chromosomes Flashcards

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1
Q

DNA

A

Deoxyribonucleic acid - a molecule. Genes and chromosomes are made of DNA.

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2
Q

Gene

A

A section of DNA that codes for 1 polypeptide

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3
Q

Chromosome

A

A long chain of genes. May also contain non-coding DNA.

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4
Q

Allele

A

Different version of a gene

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5
Q

Chromosomes are found in homologous pairs. What does this mean?

A

They have the same genes, but not necessarily the same alleles.

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6
Q

Loci

A

The place on a chromosome where a gene is found

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7
Q

DNA is packaged with…

A

proteins called histones

only in the nucleus of eukaryotic cells!!!

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8
Q

Breakdown of a chromosome in an eukaryotic cell

A

See Notion

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9
Q

How is DNA different in a prokaryotic cell?

A 
1 loop of DNA
No homologous pairs
No histones
No nucleus
DNA is shorter than in eukaryotic cells
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10
Q

How does DNA work?

A
  • DNA stores information
  • The information is in the order of the bases
  • That information is a code for how to make proteins
  • One gene is a stretch of DNA that contains the information to make one polypeptide
  • The order of bases in the gene is a code for the order of amino acids in the protein
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11
Q

Base triplet code quick summary

A

A sequence of 3 bases is a code for an amino acid. The three bases are referred to as a codon.

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12
Q

Key features of the base triplet code

A

Non-overlapping
Includes start and stop codons
Degenerate - some amino acids have more than one codon
Universal - all organisms use the same code

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13
Q

Mutation

A

a change in the structure of the DNA

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14
Q

Gene mutation

A

a change in the sequence of bases in a gene

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15
Q

When do mutations usually happen?

A

During DNA replication before mitosis/meiosis

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16
Q

Germ line mutation

A

Mutations in gametes due to mistakes in meiosis

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17
Q

Somatic mutation

A

Mutations in somatic cells due to mistakes in mitosis

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18
Q

Most cancers are linked to which type of mutation?

A

Somatic mutations

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19
Q

Why are germ line mutations arguably worse than somatic mutations?

A

Germ line mutations are passed onto the next generation - potentially subsequent generations too!

20
Q

Gene mutations lead to…

A

changes in the sequences of bases in the DNA, and therefore a change in the primary structure of the protein encoded by that gene

21
Q

Substitution

A

This can be silent (no consequences).
One base gets swapped out for another.

They can lead to a change in the primary structure of a protein –> change in bonds forming between R groups –> change tertiary structure –> change function.

Substitution can also lead to a protein being cut short (mutates into a stop codon)

22
Q

Deletion

A

Leads to a frameshift - all codons after the mutations are going to be affected.
Insertion of a base can also lead to a frameshift.

23
Q

Examples of mutagens

A

Chemicals

  • nitrous acid: changes C into U by removing a chemical group
  • benzopyrene: makes G unable to pair with C, so DNA polymerase inserts any other base instead

Radiation
- ionising radiation creates free radicals which alter the shape of bases so that DNA polymerase can’t act on them

24
Q

Chromosome mutation

A

Changes in whole sets of chromosomes

25
Q

Down’s syndrome is due to a mistake that happens in…

A

meiosis

26
Q

Polyploidy

A

Organisms having more than 2 sets of chromosomes. Occurs almost exclusively in plants.

27
Q

The sugar-phosphate backbone is joined together via…

A

phosphodiester bonds

28
Q

How does the genetic code work?

A

3 bases code for an amino acid (primary structure) and is called a codon
Universal & degenerate
There are start & stop codons

29
Q

The three stages of protein synthesis in order are…

A
  1. Transcription
  2. Splicing
  3. Translation
30
Q

Transcription in a nutshell

A

A copy of the gene is made out of RNA.

This can leave the nucleus and go to the ribosome in the cytoplasm.

31
Q

Transcription in detail

A
  1. Original DNA molecule has a coding strand and a template strand
  2. DNA molecule separates
  3. An RNA molecule is built using the template strand
  4. RNA polymerase joins the RNA nucleotides together
  5. The pre mRNA molecule detaches from the DNA molecule
32
Q

What’s unique about splicing?

A

Only in eukaryotic cells

33
Q

What is splicing?

A

Making modifications to the pre mRNA before it leaves the nucleus (i.e. removing bits that don’t code for proteins)

34
Q

What is pre mRNA?

A

A copy of the gene containing introns and exons

35
Q

What are introns?

A

Regions that don’t code for a protein in eukaryotes

36
Q

What are exons?

A

Regions that code for a protein in eukaryotes

37
Q

What is mature mRNA?

A

The end product of splicing

38
Q

How does the mRNA leave the nucleus after splicing?

A

Via the nuclear pores

39
Q

Structure of tRNA

A

Amino acid at the top, anticodon at the bottom

40
Q

2 things the anticodon on tRNA is complementary to

A
  1. the codon for the amino acid attached at the other end of the tRNA
  2. the codon of the mRNA
41
Q

What are ribosomes made of (cells recap!)

A

Proteins and ribosomal RNA (rRNA)

42
Q

Translation in detail

A
  1. Small subunit of ribosome binds to mRNA
  2. tRNA molecule arrives
  3. Large subunit arrives
  4. Anticodon of tRNA binds with codon of the mRNA that it is complementary to
  5. Another tRNA arrives at the ribosome
  6. A peptide bond forms between the two amino acids once the codon and anticodon have joined together
  7. tRNA leaves the ribosome leaving the amino acid behind
  8. Ribosome shifts along by one codon after the bond has formed
  9. Process continues until the stop codon is reached
43
Q

Where exactly is the mRNA during translation?

A

BETWEEN the large & small subunit, NOT DIRECTLY ATTACHED TO THE SMALL SUBUNIT!!

44
Q

What happens when the STOP codon is reached during translation?

A

The ribosome detaches & so does the polypeptide chain

45
Q

What needs to happen to a protein after it has been synthesised on a ribosome so that it is ready to carry out its job?

A
  1. Add prosthetic groups (some - eg. haemoglobin)
  2. Folded up into specific 3D structure (tertiary)
  3. Bind to a carbohydrate (glycoproteins)
46
Q

Where do the modifications to the protein after translation take place?

A

Some in the cytoplasm

Can also happen in the Golgi (when molecules need to be added)

47
Q

T or F: only one ribosome can work on one mRNA molecule

A

FALSE!

Several ribosomes can work on an mRNA molecule at the same time

Biology (42 decks)

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