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Nucleic Acids > Hormones That Act Within The Cell > Flashcards

Hormones That Act Within The Cell Flashcards

1
Q

What are the two types of hormone that act within the cell?

What is significant about both classes?

A
  1. steroid hormones
  2. thyroid hormones

Both classes of hormones are hydrophobic

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2
Q

What are steroid and thyroid hormones derived from?

A

Steroid hormones are derived from cholesterol

Thyroid hormones are derived from tyrosine within the protein thyroglobulin

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3
Q

What are the two types of steroid hormones?

A
  1. androgens

2. oestrogens

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4
Q

What is the difference between androgens and oestrogens?

A

Oestrogens have an aromatic ring, introduced by aromatase

Androgens do not

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5
Q

How is a receptor-hormone complex formed by a steroid hormone?

A
  1. Steroid hormone enters the cell by simple diffusion
  2. It binds to a complementary-shaped receptor in the cytosol or nucleus
  3. This forms a receptor-hormone complex
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6
Q

What happens to the steroid hormone when it binds to the receptor?

Why is this significant?

A

The shape of the hormone is changed slightly

This allows it to bind to DNA in the nucleus

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7
Q

What will the receptor-hormone complex bind to in the nucleus?

A

The hormone response element (HRE)

This is a short sequence of DNA within the promoter region of a gene

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8
Q

How does the hormone-receptor complex act as a transcription factor?

A

When it binds to the HRE, the HRE then stimulates binding of DNA polymerase and transcription of mRNA

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9
Q

What are the domains that nuclear hormone receptors are divided into?

A
  1. N-terminal domain
  2. DNA binding domain
  3. Hinge region
  4. Ligand binding domain
  5. C-terminal domina
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10
Q

What is present at the N-terminal domain of the nuclear hormone receptor?

A

A transcription regulation domain

This interacts with other proteins that regulate transcription

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11
Q

What is present at the DNA binding domain of the nuclear hormone receptor?

A

Zinc fingers which bind to the DNA helix

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12
Q

What are zinc fingers?

A

Loops of protein containing a Zn2+ ion that is coordinated with 4 cysteine residues

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13
Q

What is present at the C-terminal domain?

A

Hormone binding domain

This makes each receptor specific to a particular hormone

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14
Q

What are the two closely related versions of the oestrogen receptor?

A

ER-alpha and ER-beta

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15
Q

What is the expression of ER-alpha and ER-beta like in normal healthy breast tissue?

A

It expresses more ER-beta that ER-alpha

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16
Q

What happens if a breast cancer strongly expresses ER-alpha?

A

It causes the tissue to become more sensitive to oestrogen

Oestrogen promotes rapid division of ER-alpha-positive breast cancer cells

17
Q

How are ER-alpha positive breast cancers detected?

A

By staining sections of tumour biopsies with antibodies against the oestrogen receptor

ER-alpha positive cells are stained brown

18
Q

How can the growth and spread of ER-alpha positive breast cancers be inhibited?

A

BY administering anti-oestrogen drugs such as tamoxifen

19
Q

Why is tamoxifen described as a pro-drug?

A

It gets converted to an active form within the body by being hydroxylated

20
Q

How does tamoxifen work?

A
  1. it binds to the oestrogen receptor
  2. the oestrogen receptor does NOT acquire a shape change
  3. The oestrogen receptor cannot bind to co-activators as it has not changed shape
21
Q

What are aromatase inhibitors used to treat?

A

Oestrogen sensitive tumours

22
Q

How do aromatase inhibitors work?

A

Aromatase introduces an aromatic ring into oestrogens

Aromatase inhibitors block the formation of the aromatic ring in oestrogens

23
Q

In breast cancers that are not ER-positive, how do they increase signalling for cell division?

A

They do this by changing the amount or properties of HER2

24
Q

What is HER2?

A

A cell-surface receptor that binds to a growth factor

25
Q

What is used to treat breast cancers that are not ER-positive?

A

An antibody is given which binds to the HER2 receptor and stops it from signalling

26
Q

How does Trastuzumab work?

A

It attaches to HER2 so cancer cells cannot grow or divide

27
Q

How do thyroid hormones from a receptor-hormone complex?

A

They bind to a receptor that is already bound to DNA

28
Q

What is the result of a thyroid hormone binding to a DNA-bound receptor?

A

The hormone-receptor complex moderates gene expression

It stimulates or prevents transcription of certain genes

29
Q

What is T4 and how is it synthesised?

A

Thyroxine

It is synthesised in the thyroid gland by combining tyrosine with iodine

30
Q

How is thyroxine (T4) converted to an active form?

A

By deiodination in the peripheral tissues

It is converted to T3

31
Q

In the nucleus, where are the thyroid hormone receptors bound to?

A

Thyroid response elements (TRE) in the DNA

32
Q

What does binding of T3 to the TREs lead to?

A

The release of proteins which will either switch off or activate transcription

33
Q

What happens when transcription is activated by TREs?

A

The repressors will leave and the activators will bind to the DNA

34
Q

Where are thyroid response elements found?

A

In the promoter regions of genes involved in heart function and energy metabolism

These genes are activated by thyroid hormones

35
Q

How are thyroid hormones synthesised?

A
  1. tyrosine is iodinated on thyroglobulin
  2. iodotyrosine molecules on thyroglobulin are crosslinked
  3. the thyroxine is cut out to produce the hormone
36
Q

What enzyme do retroviruses contain?

What is the function of this enzyme?

A

Reverse transcriptase

It allows them to convert RNA into DNA once entering a cell, so the retroviral DNA can integrate into the host DNA

37
Q

What happens if a retrovirus incorporates host DNA into its sequence?

A

This produces infectious RNA viruses

They carry and express a host gene in the next cell they infect

38
Q

How may a retrovirus become capable of causing cancer?

A

If the virus captures a version of a protein that is involved in growth control

39
Q

What human protein can act as an oncogene that will cause cancer from a retrovirus?

A

A mutated version of the thyroid hormone receptor

Nucleic Acids (4 decks)

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