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Biology AQA AS > Chapter 8 DNA and Protein synthesis > Flashcards

Chapter 8 DNA and Protein synthesis Flashcards

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1
Q

What is a gene?

A

Section of DNA that contains a code for making a polypeptide and functional RNA. The code is a specific sequence of bases.

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2
Q

What is a locus?

A

Location of a particular gene on a chromosome is called the locus.

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3
Q

What is an allele?

A

One of a number of alternative forms of a gene.

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4
Q

What is a chromosome?

A

In a eukaryotic cell nucleus, DNA is stored as chromosomes.

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5
Q

What is a homologous pair?

A

They are a pair of chromosomes with exactly the same size, and have exactly the same genes but might have different alleles.

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6
Q

What is a histone?

A

The protein that DNA is wrapped around.

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7
Q

Describe DNA in prokaryotic cells.

A

DNA is in chromosomes.
DNA molecules are shorter and circular.
DNA is not wound around histones.
It supercoils to fit into cell.

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8
Q

What is the DNA in mitochondria and chloroplasts like?

A

It is short and circular and also not wrapped around histones.

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9
Q

How is the genetic code degenerate?

A

Each amino acid is coded for by more than one triplet of bases.

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10
Q

How is the genetic code universal?

A

The same triplet of bases code for the same amino acid in all organisms.

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11
Q

How is the genetic code non-overlapping?

A

Each base in a gene is only part of one triplet of bases that codes for one amino acid. Therefore each codon is read as a discrete unit.

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12
Q

What are introns?

A

Sections of DNA that do not code for amino acids and therefore polypeptide chains. Introns are only found in eukaryotic DNA.

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13
Q

What are Exons?

A

Sections of DNA which do code for amino acids.

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14
Q

What is the genome and the proteome?

A

An organisms complete set of DNA in one cell and the proteome is the full range of proteins in one cell.

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15
Q

What is RNA?

A

A polymer of a nucleotide formed of ribose, a nitrogenous base and a phosphate group

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16
Q

What bases does RNA contain?

A

Adenine, guanine, cytosine and uracil.

17
Q

What is the function of RNA?

A

It is to copy and transfer the genetic code from DNA in the nucleus to the ribosomes.

18
Q

What is mRNA?

A

A copy of a gene from DNA.

19
Q

Why is mRNA short lived?

A

As it is only needed temporarily to create a protein.

20
Q

Describe the structure of mRNA.

A

It is single stranded and every 3 bases in the sequence code for a specific amino acid. These 3 bases are called codons.

21
Q

What is the structure of tRNA?

A

Single stranded but folded to create a cloverleaf shape. This shape is held together by hydrogen bonds.

22
Q

What is the function of tRNA?

A

To attach to one of the 20 amino acids and transfer this amino acid to the ribosome to create the polypeptide chain.

23
Q

What is the anticodon in tRNA?

A

Specific amino acids attach to specific tRNA molecules and this is determined by three bases found on the tRNA which are complementary to three bases on mRNA. These are called the anticodon.

24
Q

Describe the process of transcription.

A
  • DNA helix unwinds to expose the bases as a template.
  • Only one chain of DNA acts as template.
  • Unwinding and zipping is catalysed by DNA helicase.
  • DNA helicase breaks hydrogen bonds between the bases.
  • Free mRNA nucleotides in nucleus align opposite exposed complimentary DNA bases.
  • Enzyme RNA polymerase bonds together the RNA nucleotides to create phosphodiester bonds.
25
Q

What happens in splicing?

A

The introns are spliced out by a protein called a splicesome. This leaves behind just exons.

26
Q

Describe how translation works.

A
  • Once modified mRNA has left nucleus it attaches to to ribosome in cytoplasm.
  • Ribosome attaches to start codon.
  • The tRNA molecule with the complementary anticodon to the start codon aligns opposite the mRNA, held in place by the ribosome.
  • Ribosome will move along the mRNA molecule to enable another complimentary tRNA to attach to the next codon on the mRNA.
  • The 2 amino acids that have been delivered by the tRNA molecules are joined by a peptide bond. This is catalysed by an enzyme and requires ATP.
  • This continues until the ribosome reaches the stop codon at the end of the mRNA molecule. The ribosome detaches and translation ends.
    Polypeptide chain is now created and will enter golgi body for folding and modification.
27
Q

Describe how independent segregation occurs

A

-Homologous pairs of chromosomes line up opposite each other at equator of cell.
-It is random which side of equator paternal and maternal chromosomes from each homologous pair lie.
-These pairs are separated, so one of each homologous pair ends up in daughter cell.

28
Q

Describe how crossing over works

A

When homologous pairs line up opposite each other at the equator, parts of the chromatids can become twisted around each other.
-This puts tension on the chromatids, causing pairs of chromatid to break.
-The broken parts of chromatid recombines with another chromatid.

29
Q

What is non-disjunction?

A

When the chromosomes or chromatids do not spit equally during anaphase.

30
Q

What is polyploidy?

A

Changes in whole sets of chromosomes.

31
Q

What is aneuploidy?

A

Changes in number of individual chromosomes.

32
Q

What is genetic diversity?

A

The number of different alleles in a population.

33
Q

What is evolution?

A

The change in allele frequency over many generations in a population.

34
Q

Describe the process of natural selection.

A

-New alleles for a gene is caused by random mutations.
-If new alleles increases the chances of individual to survive in that environment, then they are more likely to survive and reproduce.
-This reproduction passes on the advantageous allele to next generation.
-As a result over many generations, the new allele increases in frequency in population.

35
Q

What is directional selection?

A

When one of the extreme traits has the selective advantage. Occurs when there is a change in environment.

36
Q

What is stabilising selection?

A

Biology AQA AS (11 decks)

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