Category: A2 Level Biology

A2 Level Biology
Cambridge International Examination

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whale meat

Scientists, film-makers team up to expose illegal international trade in whale meat

In October 2009, a man and two women walked into a renowned Los Angeles restaurant called The Hump and ordered some sushi. This seemingly innocuous act was the start of a fascinating chain of events that would involve hidden cameras, genetic sequencing, a few arrests, and the first solid proof of an illegal international trade in whale meat.

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parasitism

Parasitism is the biology term used to describe the relation between two different kinds of organisms in which one receives benefits from the other by causing damage to it.

Eg. Mosquitoes, and Plasmodium—the parasite that causes malaria. This is an excellent example of how multiple species can be tied together in complex ecological interactions.

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Cellular Respiration

Metabolism

The relationship between photosynthesis and respiration. The synthesis of ATP and ADP and inorganic phosphate, and its role as the immediate source of energy for biological processes.

  • ATP is required for endothermic processes, but can be re-synthesized when coupled to exothermic processes.
  • ATP is synthesized across the inner membranes of the mitochondria and chloroplasts, hence they are adapted to give the maximum surface area. AT[ase enzymes are powered by a proton gradient that provides the energy for ATP synthesis.
  • NADH (NADPH is used in photosynthesis) and FADH2 are reduced co-enzymes that are used to carry electrons to a different part of the organelle.

Cellular Respiration

Respiration as the process by which energy in organic molecules is made available for other processes within and organism. The structure and role of mitochondria in respiration. The biochemistry of aerobic respiration only in sufficient detail to show that:

  • Glycolysis involves the oxidation of glucose to pyruvate with a net gain of ATP and reduced NAD. Pyruvate combines with co-enzyme A to produce acetyl co enzyme A.
  • Acetyle coenzyme A combines with four-C molecule to produce six-C molecule which enters Krebs production of ATP and reduced coenzyme (NAD or FAD).
  • Synthesis of ATP is associated with the electron transport chain.

Learn the 4 stages of aerobic respiration

  1. Glycolysis (in the cytosol)
  2. The link reaction in the matrix: pyruvic acid reacts with coenzyme A to form Acetyl coenzyme A and release CO2
  3. Kreb cycle in the matrix
  4. Electron transport chain in the cristae.

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End of Protein Synthesis. Then what?

Breakdown of mRNA

  • Each mRNA molecule is read many times over before being eventually breakdown by an RNase enzyme.
  • The cell can therefore only continue to make the same protein if new mRNA molecule continue to pass out from the nucleus.
  • To decrease the rate of protein synthesis, few of the mRNA molecule coding for it are made in a given time.
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Protein Synthesis 5: tRNA

  • About 80 nucleotides in length and are made under the direction of genes in thechromosomes.
  • Different tRNA molecule for each of the different possible anti-codons because of the degeneracy of the genetic code.
  • Anti-codon at the base of each tRNA must make a perfect complementary match with the codon on the mRNA before the amino acid is released.
  • Once released, the amino acid is added to the growing polypeptide chain by enzymes.
  • Since there is different kinds of tRNA for each amino acids there must be at least 2kinds of tRNA.
  • tRNA molecule is folded back on itself giving a complex 3-D shape.
  • Each tRNA molecule must be able to combine with:
  1. One of the 20kinds of amino acid
  2. mRNA codon that specifies the amino acid
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Protein Synthesis 3: RNA Polymerase

Transcription과 Translation과정을 자세히 알아보자.

1. Transcription에 사용되는 Enzyme: RNA Polymerase

  • Transcription is the process by which the code contained in the DNA molecule is transcribed into a mRNA molecule.
  • Under the control of the cell’s metabolic processes.
  • The gene must be activated before this process can begin.

2. The role of RNA Polymerase

  1. Enzyme that directly controls the process
  2. Moves 3’–>5’ direction
  3. Makes a strand of mRNA using the single strand of DNA (template strand) –Only transcribe a gene length of DNA at a times.
  4. Recognizes start and stop codes at the beginning and end of the gene.
  5. Only enzyme involved in mRNA synthesis.
  6. Unwinds the DNA

3. Terms

  • Template strand: contains the information for the construction of a protein
  • Coding strand: DNA has nucleotide sequence complementary to the template strand.
  • mRNA: Complementary to the template strand. Containing same ‘message’ as the coding strand.

4. DNA처럼 RNA도 5′–>3’방향으로 자란다. (3′–>5′ 읽어나가기 때문에..)

  • RNA grows in 5’–>3’ direction by adding new nucleotides to the 3’ end.
  • Two polynucleotide strands are anti-parallel.
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Protein Synthesis 2: Translation

NCEA LV2에서 배웠기때문에 Protein Synthesis가 생소하지는 않겠지만 Gene expression을 이해하려면 모든 과정을 디테일하게 알아야 헷갈리지 않는다. Animation을 보면서 3D로 이해해보자.

and bit of Mutation

  • •mRNA travels from the nucleus where it is formed to ribosomes in the cytoplasm.
  • tRNA, found in the cytoplasm, carries a particular amino acid that is related to its particular anti-codon.
  • An anti-codon is part of tRNA molecule and consists of 3 bases that pair with the complementary codon on mRNA.
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Protein Synthesis 1: Transcription

The transfer of the genetic code occurs in 2stages:

1. Transcription: The code in DNA is transcribed or copied into mRNA, which travels of the cell nucleus to the ribosomes in the cytoplasm.

2. Translation: At the ribosomes, the code in mRNA is translated into a specific amino acid sequence in a protein.

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Transcription

  • The genetic code in DNA is transcribed into molecule of mRNA.
  • mRNA molecule is a single strand of nucleotides joined together.
  • The order of nucleotides in an mRNA molecule is determined by the order of nucleotides in the DNA molecule from which the mRNA has been transcribed.
  • Four different kinds of nucleotides are found in RNA: (A) Adenine, (U)Uracil, (C) Cytosine, (G) Guanine
  • No thymine found in RNA strand.

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Splicing

• Initially, the RNA copy of a gene includes both introns and exons.

•Introns are removed and the exons are spliced together to make a continuous strand of mRNA.

•After removal of the introns, the RNA leaves the nucleus via the pores in the nucleus envelope and passes to the cytoplasm.

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DNA Replication Process Steps (1)

DNA Replication process steps:

1.Unwinding the DNA molecule

2.Making new DNA strand

3.Two new double-helix DNA molecule

*In cell division, two DNA strands appear as sister chromatids joined at a centromere.

Make sure you understand Semi Conservative model: Two daughter strands of DNA will each have one old strand from the parent DNA and one newly formed strand.