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BIOL5 > Control Of Gene Expression > Flashcards

Control Of Gene Expression Flashcards

1
Q

What are multipotent cells?

A

Cells that can differentiate to form many different types of specialised cell. These are found in adult bone marrow, skin and the lining of the small intestine.

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2
Q

How do cells become differentiated?

A

Some genes are switched on and others are switched off

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3
Q

How many stem cells do plants have?

A

Plants contain many stem cells which can help to form clones

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4
Q

Look over how embryonic stem cells can be used in medicine p238.

A

Done!

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5
Q

How does oestrogen encourage gene transcription?

A
  • Oestrogen is a lipid soluble molecule and diffuses easily through the phospholipid portion of the cell-surface membrane
  • The oestrogen combines with a site on a receptor molecule of the transcriptional factor with a complementary shape
  • The oestrogen changes the shape of the receptor molecule, which releases the inhibitor molecule from the DNA binding site on the transcriptional factor
  • The TF enters the nucleus through a pore to combine with DNA
  • This stimulates transcription
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6
Q

How does siRNA prevent gene expression?

A
  • An enzyme cuts large double-stranded molecules of RNA into smaller sections called siRNA
  • One of the two siRNA strands combines with an enzyme
  • The siRNA molecule guides the enzyme to the mRNA by pairing up its bases with complementary ones on the section of the mRNA molecule
  • The enzyme cuts the mRNA into smaller sections so it can no longer be translated into a polypeptide so the gene can not be expressed
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7
Q

How can siRNA be used medically?

A
  • To identify the roles of genes in biological pathways

* To use siRNA to block genes and prevent disease

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8
Q

What are totipotenent cells?

A

Cells that can differentiate to form any type of specialised cell. These are found in embryos.

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9
Q

How is MRNA adapted for its function?

A

It possesses the correct sequences of organic bases that code for specific polypeptides
It is easily broken down

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10
Q

How does DNA compare with MRNA and TRNA?

A

Double stranded – single stranded – single stranded
Largest – middle- smallest
Double-helix – single-helix – clover shaped
Deoxyribose sugar – ribose sugar – ribose sugar
Found in nucleus - made in nucleus but found throughout the cell – made in nucleus but found throughout the cell
Chemically stable – chemically unstable – in the middle
Read p222 for TRNA description

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11
Q

Describe the process of transcription.

A
  • DNA Helicase breaks the hydrogen bonds between bases, causing the two strands to separate
  • RNA polymerase moves along one of the DNA strands (the template strand), bringing in free complementary nucleotides
  • The DNA strand recoils behind the RNA polymerase
  • When the RNA polymerase reaches the stop codon, it detaches and the production of pre-MRNA is complete
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12
Q

Why must splicing occur after transcription?

A

Exons code for proteins and introns do not
Introns would interfere with the synthesis of the protein so they are removed in splicing
Mutations can affect the splicing of mRNA, which is why some diseases occur

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13
Q

Describe the process of translation.

A
  • MRNA leaves the nucleus via the nuclear pores
  • It is attracted to the ribosomes and attaches to them at the start codon
  • The TRNA molecule with a complementary anticodon sequence pairs up with the sequence on the MRNA
  • The molecule with a complementary anticodon sequence pairs to the next codon, carrying another amino acid
  • Using an enzyme and ATP, the two amino acids on the TRNA are joined by a peptide bond
  • The amino acids are continually linked together as the ribosome moves along the mRNA
  • As the peptide bonds form, the TRNA molecule is released and is free to collect another amino acid from the cell
  • This continuous until a stop codon is reached, at which point the ribosome, MRNA and last TRNA molecule all separate and the polypeptide chain is complete
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14
Q

What are the three forms of gene mutation (substitution)?

A

Nonsense mutation – occurs if a base change results in the formation of a stop codon so the synthesis of the polypeptide is stopped prematurely
Mis-sense mutation – arises when a base change results in a different amino acid being coded for, which affects the tertiary structure of the protein
Silent mutation – arises when a base change results in the same amino acid being coded for

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15
Q

How does gene mutation (deletion) occur?

A

If one of the bases is lost from the DNA sequence, a frame-shift occurs and an entirely new protein may be synthesised

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16
Q

What are the causes of mutations?

A
  • Typically occur spontaneously during DNA replication but we can increase their frequency
  • Mutagenic agents include high-energy radiation that disrupts the DNA molecule and chemicals that interfere with transcription or alter the DNA structure
  • Whilst mutations produce variation, they often produce an organism less suited to its environment
17
Q

Which two genes is cell division controlled by?

A

Proto-oncogenes which stimulate cell division

Tumour suppressor genes that slow cell division

18
Q

How is cell division controlled in a normal cell/in an abnormal cell?

A
  • Growth factors attach to a receptor protein on the cell-surface membrane and switch on the genes necessary for DNA replication
  • A gene mutation can cause proto-oncogenes to mutate into oncogenes which permanently activate the receptor protein on the cell membrane, so cell division is switched on in the absence of growth factors
  • The oncogene may also code for a growth factor that can be produced in excessive amounts, again stimulating excessive cell division
19
Q

What is the role of tumour suppressor genes?

A
  • They inhibit cell division - Can become mutated and therefore inactivated, so the rate of cell division increases
  • Most mutated cells die but any that survive are capable of making clones of themselves and forming tumours
  • Malignant tumours are harmful, whilst benign tumours are harmless

BIOL5 (6 decks)

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