cell differentiation

totipotent

can differentiate into any type of cell

eg cells in zygote / all plant tissue

issues with embryonic stem cells

ethical issues. cannot conesnt, some believe that life starts at conception

Stem cell defintion (3)

undifferentiated cells

capable of continuous division

divide to renew themselves over long periods of time and can develop into other specialised cell types

pluripotent deifinition and example

• can differentiate into a limited number of specialised cells

• eg embyonic / fetal

multipotent

• can differentiate into a limited number of specialised cells

• eg bone marrow producing any type of blood cell

unipotent

• can only differentiate into a single type of cell

• eg cardiomyocyte

explain induced pluripotent cells (3)

• pluripotent stem cell that is produced from unipotent stem cells eg. any body cells

• cells are genetically altered in a laboratory by inducing genes and transcriptional factors within cellls to express themselves

• are capable of self renewal, therefore theoretically provide limitless supply

Pros (2) and cons (3) of stem cells treating human disorders

pros:

• do not require donors for organ transplants

• less / no chance of rejection

cons:

• possibility of uncontrolled cell division

• ethical debate regarding use of human embryos

• iPS are new technology, long term effects are unknown

somatic cell definition

diploid, specialised cellthat has been differentiated to become specialised to perform specific functions

all somatic cells are genetically identical

gene expresion is controlled by (3)

1. epigenetics

2. regulating translation

3. regulating transcription

explain regulating transcription (6)

• promotor region of a gene regulates expression

• oestrogen diffuses into the cell through the phospholipid bilayer

• attaches to the inactive transcription factor

• activated transcription factor enters nucleus through nuclear pores

• attaches to promotor region

• allows for RNA polymerase to begin transcription

Transcription factor (3)

• molecules (usually proteins) that bind to the promotor region

• which allow RNA polymerase to bind to the gene and intitiate transcription

• can be activated or inhibited by other molecules

regulation of translation (7)

1. Occurs if theres a high concentration of mRNA in cytoplasm

2. double stranded RNA is produced

3. is hydrolysed by enzymes, producing short lengths of double stranded RNA (siRNA)

4. one strand, which is complimentary to mRNA attaches to enzymes

5. single stranded siRNA attaches to the mRNA

6. mRNA can’t be translated

7. polypeptide / protein is not produced

Enzymes involved in regulating translation (3)

• RNA dependent RNA polymerase

• Dicer

• Argonaut

Chromatin

composed of DNa molecules wrapped around histone proteins

structure can be altered so that nucleosomes are closer together or further apart

nucleosomes being further apart allows them to be expressed

nucleosomes

strands of DNA wrapped around histone

epigenome and examples

chemical tags which attach to DNA or histone proteins

examples: acetyl and methyl groups

explain methylation and demethylation of DNA

• methylation causes chromatin to become more condensed, so harder for DNA to be transcribed. gene is silenced

• demethylation causes chromatin to be less ocndensed, easier for DNA to be transcribed, so genes are expressed

explain deacylation and acylation of HISTONES

• deacylation causes chromatin to become more condensed, so harder for DNA to be transcribed. gene is silenced

• acylation causes chromatin to be less ocndensed, easier for DNA to be transcribed, so genes are expressed

explain the results of the rat licking experiment

1. high licking and grooming / low licking and growing

2. increases serotonin / decreases serotonin

3. enzymes activated / enzymes not activated

4. DNA is unmethylated / DNA stays methylated

5. GR expressed / GR unexpressed

6. low conc. cortisol and low anxiety / high conc. cortisol and anxiety

Genome

all genes in a cell

Proteome

full range of proteins a cell / tissue / organism can produce

Mutation definition

Random change in DNA base sequence

When do mutations occur

Interphase / DNA replication

Consequence of DNA mutation (6)

1. Change in DNA base sequence

2. Change in sequence of mRNA codons

3. Change sequence of amino acids in polypeptide chain

4. Changes position of ionic / disulfide bonds

5. Changes in tertiary structure of protein

6. Protein is non-functional

Types of dna mutation (6)

1. Substitution

2. Deletion

3. Addition

4. Duplication

5. Inversion

6. Translocation

Substitution definition

One nucleotide base is incorrectly copied

Changes only one amino acid

May not change sequence due to degenerate code

Deletion definition

One nucleotide base isn’t copied

frame shift

All amino acids that downstream from the mutation are changed

Polypeptide chain would be shorter (or longer if stop codon removed)

Additional definition

Additional nucleotide base is inserted into the new DNA

Frame shift

Polypeptide chain is longer

Duplication definition

Sequence of bases copied multiple times

Sequence of amino acids duplicated

Polypeptide chain is longer

Inversion definition

Sequence of bases is inverted

Amino acids duplicated Polypeptide sequence is reversed

Translocation definition

Sequence of bases is transferred to different chromosome

How can a mutation be silent (4)

• mutation occurs in intron

• Degenerate DNA code

• Inversion: sequence is palindromic

• Change of shape occurs not in active site, so protein is still functional

Describe proto-oncogenes (5)

• codes for growth hormone and growth hormone receptors, and growth factors

• Which promote progression of the cell cycle

• Initiate DNA replication

• Stimulate cell division

• Inhibit apoptosis

Describe tumour surpressor genes (3)

• code for proteins that inhibit progression of cell cycle

• Inhibit DNA replication and cell division

• Stimulate apoptosis

Describe benign tumours (4)

• grow in one place and do not spread

• Grow slowly and are surrounded by capsule (primary tumour)

• Non cancerous

• Treatment usually involves surgery

Describe malignant tumours (4)

Have cells which break off and spread around the body (metastasis)

Grow rapidly and not surrounded by capsule

Cancerous and form secondary tumours

Treatment involves surgery and chemotherapy or radiotherapy

How can mutations to proto oncogenes cause cancer

Proto oncogenes mutate to form oncogenes

Permanently activated / expressed

Imcreases production of proteins that stimulate DNA replication and cell division

Treatment of breast cancer (6)

1. Inhibit enzyme that synthesises production of oestrogen

2. Inhibit the ERa transcription factor, binding to ERa so oestrogen can’t bind, inhibiting growth of tumour

3. Use siRNA to prevent translation of oncogenes

4. Epigenetic drugs to methylate oncogenes or acylate tumour surpressor genes

5. Monoclonal antibodies to bind ro growth factor receptor