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SNAB biology hoe > 3C Differentiation and Variation > Flashcards

3C Differentiation and Variation Flashcards

1
Q

stem cell

A

undifferentiated cell with potential to continue to DIVIDE to become specialised cells with one function

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2
Q

differentiated cell

A

cell with one purpose -> cannot become multiple cells

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3
Q

totipotent

A

stem cells that can become ALL cells

  • embryonic stem cells that can differentiate into any cell type in embryo
  • … and extra-embryonic cells (cells that make up placenta and umbilical cord)

“i can totally be pregnant” -> embryonic cells

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4
Q

pluripotent

A

stem cells that can become MOST cells

  • embryonic stem cells that can differentiate into any cell type found in an embryo
  • but NOT able to differentiate into cells forming placenta and umbilical cord
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5
Q

(multipotent)

A

stem cells that can become SOME cells

adult stem cells that have LOST SOME OF POTENCY associated with embryonic stem cells and are no longer pluripotent

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6
Q

explain why some cells do not remain totipotent

A

during fertilisation and cell division -> become specialised for a purpose

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7
Q

state 3 examples of multipotent stem cells in humans

A
  • nerve cells
  • muscle cells
  • bone marrow
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8
Q

explain how “potency” of plant and animal cells differ

A

animal cells: once specialised, it is usually permanent

plant cells: become specialised and unspecialised throughout lifetime

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9
Q

describe potential uses of stem cells in medicine

A
  • used to regrow limbs, organs
  • cure degenerative diseases

v useful as no chance of rejection (unlike donor organs)

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10
Q

explain why PLURIPOTENT EMBRYONIC stem cells could be considered more useful than ADULT MULTIPOTENT stem cells

A
  • embryonic stem cells -> can turn into more types of cells than body cells
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11
Q

discuss the ethical views on the use of embryonic stem cells

A

obtaining stem cells from embryos created via IVF raise ethical issues as procedure destroys viable embryo

FOR:

  • embryos will be destroyed anyway
  • advancing science with hope of saving lives

AGAINST:

  • mothers pressured into donating eggs
  • murder? -> on religious grounds
  • ppl believe that at moment of fertilisation: genetically unique individual created -> has a right to life
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12
Q

why aren’t stem cells rejected by body?

A

DNA is from YOU -> not recognised as foreign

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13
Q

what are the dangers of stem cell therapy?

A
  1. stem cells becoming cancerous
  2. body may reject stem cells
  3. when injecting stem cells -> risk of introducing INFECTION
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14
Q

activators

A

factors that increase rate of transcription

  • help RNA polymerase bind to DNA and begin transcription
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15
Q

repressors

A

factors that decrease rate of transcription

  • prevent RNA polymerase binding to DNA and stopping transcription
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16
Q

where do transcription factors bind to in EUKARYOTES (animals and plants)?

A

specific DNA sites near START of TARGET GENES (genes they control expression of)

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17
Q

where do transcription factors bind to in PROKARYOTES?

A

OPERONS

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18
Q

operon

A

section of DNA that includes…

  • cluster of structural genes that are transcribed together (these code for useful proteins e.g. enzymes)
  • control elements -> including a PROMOTER REGION (a DNA sequence that RNA polymerase initially binds to)
    -> OPERATOR REGION (where transcription factors bind)
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19
Q

lac operon

A

controls production of enzyme LACTASE and 2 other structural proteins

where genes that produce enzymes needed to respire lactose are found

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20
Q

promoter

A

DNA sequence located BEFORE structural genes that RNA POLYMERASE binds to

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21
Q

operator

A

DNA sequence that TRANSCRIPTION FACTORS bind to

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22
Q

E. coli

A

bacterium that respires glucose BUT will use lactose if glucose isn’t available

23
Q

name lac operons structural genes

A
  • lacZ
  • lacY
  • lacA

they produce proteins that help bacteria digest lactose

24
Q

potency

A

ability of stem cells to differentiate into more specialised cell types

25
Q

how are epigenetic changes to a cell’s gene expression passed on?

A
  • when a cell ÷ and replicates …
  • epigenetic changes to its gene expression passed on to daughter cells
  • certain genes that are activated / deactivated in o.g cell will also be activated / deactivated in daughter cells
  • so daughter cells equipped to deal with changed env in same way as o.g cell was
26
Q

differentiation

A

proccess by which a cell becomes specialised

27
Q

where are totipotent stem cells present?

A

first few cell ÷ of an embryo

28
Q

how do stem cells become specialised?

(1 mark)

A

different genes in their DNA become active and get expressed

29
Q

how are stem cells specialised in animals and plants?

A
  • when chemical stimulus present -> some genes activated / others inactivated (differential gene expression)
  • transcription occurs at active genes
  • active mRNA from active genes translated on ribosome to synthesise proteins
  • protein modifies cell and determines structure and functions
  • changes to cell produced by these proteins cause cell to become specialised
30
Q

discuss the way society uses scientific knowledge to make decisions about the use of stem cells in medical therapies

(6 marks)

A
  • looking at proposals of research and deciding if they should be allowed -> ethical issues into account
    -> ensures research isn’t unnecessarily repeated by diff groups
  • licensing and monitoring centres -> ensures only fully trained staff carry out research
    -> staff won’t waste precious resources eg. embryos
    -> helps avoid unregulated research
  • guidelines / codes of practice -> all scientists working in similar manner
    -> ensures scientists using acceptable source of stem cells and method to extract cells are controlled (includes max. age of embryo that can be used)
  • monitoring developments
    -> ensures changes in field regulated appropriately and all guidelines up to date
  • providing info / advice to governments / professionals
    -> helps promote science involved in embryonic research
    -> helps society understand what’s involved / why it’s important
31
Q

adult stem cells can only develop into a limited range of cells whereas embryonic stem cells can develop into all types of specialised cells.

suggest why adult stem cells might be used instead of embryonic stem cells

A

if patient needs stem cell transplant and own stem cells can be used -> less risk of rejection

as cells are not foreign (‘self’) and doesn’t initiate immune system response

32
Q

describe how stem cells can be used to treat a range of diseases

A
  • stem cells can differentiate into any cell type -> so can be used to replace damaged tissue in range of diseases
  • eg. leukemia (cancer of bone marrow) kills bone marrow stem cells -> so bone marrow transplants given to replace them
33
Q

what conditions are scientists researching for stem cell treatment?

A
  • spinal cord injuries
    -> stem cells could be used to repair damaged nerve tissue
  • heart disease and damage caused by heart attacks
    -> replace damaged heart tissue
34
Q

explain one benefit of using embryonic stem cells instead of adult stem cells

A

embryonic stem cells can develop into all types of specialised cell

whereas adult stem cells can only develop into a limited range of cells

35
Q

state 2 reasons why some ppl are opposed to using embryonic stem cells

A
  • believe embryos have a right to life from moment of fertilisation
  • believe its wrong to destroy viable embryos
36
Q

RBCs contain lots of haemoglobin and have no nucleus (to make room for more haemoglobin).

they are produced from a type of stem cell in the bone marrow.

describe how a red blood cell becomes specialised

A
  1. stem cell in bone marrow produces new cell where genes for haemoglobin production activated
  2. other genes (eg. those involved in removing nucleus) activated too
  3. many other genes activated / inactivated -> leads to specialised RBC
37
Q

what is the variation in phenotype influenced by?

A

variation in genotype (genes) and the env

(phenotype produced by interactions of env and genotype)

38
Q

locus

A

location of genes on chromosome

39
Q

explain the type of variation shown by human blood groups

(3 marks)

check this

A

discontinuous variation

-> blood groups: A, B, AB, O

monogenic characteristics (controlled by one gene) so blood groups show this type of variation

  • blood groups only influenced by genotype (not env)
40
Q

discontinous variation

A
  • when 2 or more distinct categories
  • each individ. falls into only 1 category
41
Q

monogenic characteristics

A

controlled by one gene

usually show discontinous variation

eg. blood group

42
Q

polygenic characteristics

polygenic inheritance

A

controlled by no. of genes at diff loci

usually show continuous variation

eg. height

43
Q

continous variation

A

when individ. in pop vary within a range -> no distinct categories

Eg.

  • height
  • mass
  • skin colour
44
Q

height is a phenotype influenced by both genotype and env.

describe how the env affects the height of an individ.

A
  • height is polygenic (controlled by no. of genes at diff loci)
  • and affected by env factors eg. nutrition
  • tall parents usually produce tall children (polygenic inheritance)
  • BUT if child undernourished: won’t grow to max. height (as protein required for growth)
45
Q

MAOA is enzyme that breaks down monoamines (chemical) in humans.

describe how the env affects the MAOA of an individ.

A
  • low levels of MAOA linked to mental health problems
  • MAOA production controlled by single gene (monogenic)
  • BUT taking anti-depressants / smoking can reduce amount produced
46
Q

risk of cancer is influenced by genotypes and the env.

suggest what env factors influence the risk of cancer

A

cancer: uncontrolled ÷ of cells -> leads to lumps of cells (tumours) forming

  • risk affected by genes
  • BUT env factors eg. diet can also influence risk
47
Q

some arctic animals have dark hair in summer but white hair in winter.

describe how the env interacts with the animals’ genotype to produce this phenotype

A
  • animal hair colour is polygenic
  • BUT env plays part in some animals
  • env factors eg. decreasing temp trigger this change BUT couldn’t happen if animal didn’t have genes for it
48
Q

describe how changes to the env can cause changes in gene expression

(4 marks)

A

in eukaryotes, epigenetic control can determine if certain genes expressed -> altering phenotype

  • epigenetic control doesn’t alter base seq DNA
    -> works by attaching / removing chemical groups to / from DNA …
  • … altering how easy it is for enzymes (and other proteins needed for transcription) to interact with and transcribe genes
  • epigenetic changes are independent -> modification in 1 area not linked to modification in another
  • epigenetic changes to gene expression play role in lots of cellular processes
    -> also occur in response to changes to env (pollution, availability of food)
49
Q

one method of epigenetic control is methylation of DNA.

describe this process

A
  • when methyl group (-CH₃) is added to DNA coding for gene
  • group always attaches at a CpG site -> where a cytosine and guanine base are next to each other in DNA
  • increased methylation changes DNA structure …
  • … so proteins and enzymes needed for transcription (transcription factors) cannot bind to gene
  • so gene not expressed (inactivated)
50
Q

one method of epigenetic control is the modification of histones.

explain why this is the case

A

histones: proteins that DNA wraps around to form chromatin -> which makes up chromosomes

  • adding/removing acetyl groups to chromatin make it highly condensed / less condensed
  • how condensed it is affects accessibility of DNA and if proteins and enzymes needed for transcription can bind to it
  • so modification of histones affects gene expression
51
Q

describe the epigenetic modifications of histones

A

include addition / removal of acetyl groups (COCH₃)

  1. when histones acetylated -> chromatin less condensed
    -> so proteins involved in transcription can bind to DNA
    -> so genes can be transcribed (activated)
  2. when acetyl groups removed from histones
    -> chromatin highly condensed
    -> genes in DNA cannot be transcribed
    -> as transcription proteins cannot bind to them
    -> so genes repressed
  3. modification of histones REVERSIBLE -> can be diff in diff cell types + varies with age
52
Q

histone

A

protein that DNA wraps around to form chromatin (which makes up chromosomes)

53
Q

epigenome

A

all epigenetic tags in an organism

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