CIE IGCSE Biology: 复习笔记:17.1.5 Which Proteins are Synthesised?

CIE IGCSE Biology: 复习笔记:17.1.5 Which Proteins are Synthesised?

Control of Gene Expression: Extended

 

Protein-synthesisProtein synthesis

  

  • Expression of a gene means whether that gene is transcribed and translated in a particular cell or not
  • Most genes are not expressed in a particular cell
    • They are 'switched off'
    • Because that would be a waste of energy and other resources in the cell
  • Only the genes whose proteins are vital to that cell's function are expressed ('switched on')

 

How-ribosomes-build-proteins

 The triplet code of DNA (carried by mRNA) is read by the ribosome and amino acids are attached together in a specific sequence to form the protein

 

  • In this way, DNA controls cell function by controlling the production of proteins
  • The proteins may be enzymes, antibodies, or receptors for neurotransmitters
  • Although all body cells in an organism contain the same genes, many genes in a particular cell are not expressed because the cell only makes the specific proteins it needs

 

Haploid and Diploid Cells

 

  • All humans have 23 different chromosomes in each cell
  • In most body cells, not including the gametes (sex cells), we have 2 copies of each chromosome, leading to a total of 46 chromosomes
  • Nuclei with two sets of chromosomes are known as diploid nuclei
  • The gametes (egg and sperm cells) only have one copy of each chromosome, meaning they have a total of 23 chromosomes in each cell
  • Nuclei with one set of unpaired chromosomes are known as haploid nuclei

 

Exam Tip

An easy way to remember the difference between haploid and diploid is to remember:

Haploid = Half the normal number of chromosomes

It’s worth noting that the human diploid chromosome number is 46. In an exam, you may be given information about a different species, with a different number of chromosomes. Make sure you read exam questions carefully.

转载自savemyexams

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