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A-Level Biology > 4 DNA, genes and protein synthesis > Flashcards

4 DNA, genes and protein synthesis Flashcards

1
Q

What is a gene?

A

A section of DNA that contains the coded information for making polypeptides and functional RNA

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2
Q

What is the genetic code?

A

The order or sequence of the 4 bases in each gene

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3
Q

Which base sequence is read to make proteins?

A

On the coding strand

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4
Q

What is a codon?

A

The sequence of three bases on mRNA that codes for a single amino acid

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5
Q

How many bases code for 1 amino acid?

A

3

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6
Q

How many possible combinations of amino acids are there but how many amino acids are there?

A

64 combinations
20 amino acids

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7
Q

What is the purpose of the extra 44 triplet codes?

A
  • A mutation (substitution) may change a base, but it results in a codon that codes for the same amino acid, so the same primary protein structure
  • 3 stop codons
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8
Q

What does degenerate mean?

A

Amino acids are coded for more than one triplet

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9
Q

What does non-overlapping mean?

A

Every 3 bases belong to only 1 codon

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10
Q

What does universal genetic code mean?

A

All living organisms have the same codons, that all code for the same amino acids

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11
Q

What is a locus?

A

DNA located at a particular position

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12
Q

What do genes code for?

A
  • Amino acid sequence of a polypeptide
  • Functional RNA, including ribosomal RNA and transfer RNA
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13
Q

What are the 4 bases in DNA?

A

Adenine, guanine, cytosine, thymine

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14
Q

What is DNA like in prokaryotic cells?

A
  • Shorter
  • Form a circle
  • Not associated with protein molecules, therefore do not have chromosomes
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15
Q

What is DNA like in eukaryotic cells?

A
  • Longer
  • Linear
  • In association with proteins called histones to form chromosomes
  • Mitochondria and chloroplasts of eukaryotic cells contain DNA like prokaryotic DNA
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16
Q

What is the structure of DNA?

A
  • Double helix
  • Helix is wound around histones to fix it in position
  • DNA- histone complex is then coiled, the coil is looped and further coiled then packed into the chromosome –> lots is condensed into a single chromosome
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17
Q

What is a homologous pair?

A

Two chromosomes that carry the same genes but not necessarily the same alleles of the genes

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18
Q

What is an allele?

A

One of a number of alternative forms of a gene

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19
Q

What is a genome?

A

Sum of all the genes that are in an organism

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20
Q

What is a proteome?

A

Sum of all the proteins that are made by the cells of an organism

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21
Q

What is RNA?

A

Ribonucleic acid
- Polymer made up of repeating mononucleotide sub-units
- Forms a single strand

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22
Q

What is RNA made up of?

A
  • Pentose sugar ribose
  • Adenine, guanine, cytosine and uracil
  • Phosphate group
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23
Q

How do single nucleotides form?

A

Pentose sugar, phosphate group and organic base are joined in a condensation reaction

24
Q

What is the bond formed between 2 mononucleotides?

A

Phosphodiester bonds - dinucleotide

25
Q

What is a chain of nucleotides called?

A

Polynucleotide

26
Q

What is DNA made up of?

A
  • Pentose sugar is deoxyribose
  • Phosphate group
  • Adenine, thymine, guanine and cytosine
  • Made up of two strands of nucleotides which are joined together by hydrogen bonds
27
Q

What are the complementary base pair rules?

A

Adenine and thymine
Guanine and cytosine

28
Q

Why is DNA a stable molecule?

A
  • Phosphodiester backbone protects the more chemically reactive organic bases inside the double helix
  • Hydrogen bonds link the organic base pairs forming bridges between the Phosphodiester uprights
  • 3 hydrogen bonds between cystine and guanine, higher the proportion of C-G more stable the molecule
  • Base stacking hold the molecule together between the base pairs
29
Q

What is the function of DNA?

A
  • Hereditary material responsible for passing genetic information from cell to cell and generation to generation.
  • Large number of base pairs so lots of variety of sequences of bases so provides genetic diversity
30
Q

What is DNA?

A

A double helix with two polynucleotide chains held together by hydrogen bonds between specific complementary base pairs

31
Q

What is the DNA structure?

A
  • 5 prime end and 3 prime end (number of the carbon of the deoxyribose at the end)
  • DNA strands are antiparallel (one goes up and the other goes down)
  • Phosphate groups make DNA acidic
32
Q

What does pyrimidines mean?

A

T and C bases - have 1 ring

33
Q

What does purines mean?

A

A and G bases - 2 rings

34
Q

Explain how the structure of DNA is related to its functions

A
  1. Sugar phosphate backbone/double stranded/helix so provides strength/stability
  2. Weak hydrogen bonds so strands can separate during replication
  3. Extremely large so can store loads of information
  4. Coiled into a helix so is compact
  5. Complementary base pairs so can replicate accurately
  6. Many hydrogen bonds so its is stable
  7. The base sequence allows information to be stored and transcribed into the correct order of amino acids
  8. Double stranded so each strand acts as a template for semiconservative replication
35
Q

What is a histone?

A

Positively charged proteins associated with DNA is eukaryotic cells
Act as spools around which the DNA wraps, which condenses the DNA into more manageable units for gene expression

36
Q

What is chromatin?

A

Consists of mainly DNA and histones - describes the structure of DNA during interphase of the cell cycle - has a small amount of mRNA

37
Q

How does DNA replicate?

A

Semi-conservative replication

38
Q

Describe the stages to DNA replication

A
  • DNA helices separates the 2 strands of DNA double helix by breaking 3 hydrogen bonds between the A and T and 2 h-bonds between the C and G
  • Each strand of DNA becomes templates for each strand of the new DNA
  • Complementary nucleotides form hydrogen bonds with the new/old exposed nucleotides using the base pairs of A,T,C and G.
  • The DNA polymerase then forms phosphodiester bonds between the nucleotides in a condensation reaction
39
Q

What must DNA do as the genetic material?

A
  • Replicate faithfully
  • Have the coding capacity to generate proteins and other products for all cellular functions
40
Q

What is the structure of ATP?

A

Adenine - a nitrogen-containing organic base
Ribose - a sugar molecule with a 5-carbon ring structure (pentose sugar) –> backbone
Phosphates - chain of 3 phosphate groups

41
Q

How does ATP store energy?

A
  • The bonds between phosphate groups are unstable so have low activation energy (easily broken)
  • Release large amount of energy
42
Q

What is the equation for the breakdown of ATP?

A

ATP (adenosine triphosphate) + H2O (water) –> ADP (adenosine diphosphate) + Pi (inorganic phosphate) + E (energy)

43
Q

What reaction is used to convert ATP to ADP?

A

Hydrolysis
Catalysed by the enzyme ATP hydrolyse
Reversible reaction

44
Q

Why and how is ATP formed from ADP?

A

ATP to ADP is reversible reaction
Energy can be used to add an inorganic phosphate to ADP to re-form ATP
Catalysed by ATP synthase
Water removed –> condensation reaction

45
Q

When does the synthesis of ATP from ADP occur?

A
  • In chlorophyll-containing plants cells during photosynthesis
  • In plant and animal cells during respiration
  • In plant and animal cels when phosphate groups are transferred from donor molecules to ADP
46
Q

Why is ATP an immediate energy source?

A

The instability of its phosphate bonds means it is not a long-term energy store
Therefore, cells do not store large quantities of ATP (rapidly re-formed from ADP and Pi)

47
Q

Why is ATP a better immediate energy source than glucose?

A
  1. Each ATP molecule release less energy than each glucose molecule - energy for reactions is release is in smaller and more manageable quantities
  2. Hydrolysis of ATP to ADP is a single reaction that releases immediate energy. The breakdown of glucose is a long series of reactions and therefore the energy release takes longer
48
Q

What is ATP used in?

A
  1. Metabolic processes
    - Provides energy to build up macromolecules from their basic units eg starch from glucose
  2. Movement
    - Muscle contraction, energy for filaments
  3. Active transports
    - Provides energy to change shape of carrier proteins in plasma membranes
  4. Secretion
    - Needed to form lysosomes necessary for secretion of cell products
  5. Activation of molecules
    - Inorganic phosphate from hydrolysis of ATP used to phosphorylate other compounds and lower activation energy
49
Q

What is an exon?

A

Coding parts of the gene that are expressed

50
Q

What is an intron?

A

Non-coding parts that are spliced

51
Q

Describe the stages of transcription

A
  • DNA helicase breaks the hydrogen bonds between the DNA strands
  • Free RNA nucleotides bind to their complementary DNA nucleotides on the coding strand
  • RNA polymerase moves down the DNA strand, and forms phosphodiester bonds between the mRNA molecules
  • Introns are removed (by splicesomes) in a process called splicing, leaving only the axons (mRNA)
  • Edited mRNA now leaves the nucleus through a nuclear pore
52
Q

Describe the process of splicing

A
  • Pre mRNA is made during transcription
  • Spliced to remove introns
  • Only axons remain in the mRNA, as these are the coding regions
  • mRNA leaves the nucleus through a nuclear pore
53
Q

In which cells does splicing happen?

A

Eukaryotic cells
Prokaryotic cells (bacteria) do not have introns

54
Q

What is translation?

A

Turning mRNA code into a polypeptide chain

55
Q

Describe the stages of translation

A
  1. Ribosome bind to mRNA at the start codon
  2. A tRNA molecule that has an anticodon that is complementary to the codon binds to the mRNA
  3. A second tRNA that has an anticodon complementary to the second codon also binds to the mRNA
  4. Each tRNA molecule brings a specific amino acid
  5. A peptide bond forms between the amino acids. Requires energy from ATP
  6. First tRNA molecule detaches from the ribosome
  7. Ribosome moves along the mRNA
  8. Next tRNA binds to the mRNA
  9. When ribosome reaches the stop codon, it detaches

A-Level Biology (19 decks)

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