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a level biology > Topic 3: Voice of the Genome Part 2 > Flashcards

Topic 3: Voice of the Genome Part 2 Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

what is a locus

A

the position that a gene holds on a chromosome

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2
Q

define homologous chromosomes

A

they are 2 chromosomes that have genes occupying the same locus and are a similar size and shape

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3
Q

outline meiosis

A

cell starts with 46 chromosomes
1. DNA replicates to give 2 identical copies of each chromosome, which is 2 chromatids
2. DNA condenses and the chromosomes arrange into homologous pairs
3. 1st division - homologous pairs are separated and 2 cells have formed
4. 2nd division - sister chromatid pairs are separated and 4 genetically different, gamete daughter cells form; each with 23 chromosomes (haploid)

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4
Q

how does meiosis produce genetically non-identical cells?

A
  1. crossing over
    it occurs before the first division
    homologous chromosomes pair up
    the non-sister chromosomes of these can cross over (forming chiasmata) and get entangled a
    this can cause a chromosome section of one chromosome to break and rejoin with the chromatid of the other chromosome

they have the same genes, but allele combinations are now different so the gametes produced will all have different alleles

  1. independent assortment
    allele combinations vary in daughter cells because homologous pairs line up randomly in the equator in meiosis
    so the maternal and paternal chromosome combinations in each cell vary; increasing genetic variation in gametes
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5
Q

what are linked genes

A

genes are linked if they have loci on the same chromosome; as they’re on the same chromosome, they’ll stay tother during independent assortment and the alleles will be passed on the the offspring together
unless they are split up by crossing over

the closer together the loci of 2 genes on a chromosome, the less likely they are to be split up by crossing over and they are said to be more closely linked

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6
Q

what are sex linked genes

A

genes/a characteristic is sex linked if the locus of the allele that codes for it is on a sex chromosome

female - XX male - XY
Y is smaller and carries fewer genes so males often have only one allele for sex-linked genes and so will express the characteristic even if its recessive

males are more likely to show recessive phenotypes for sex-linked genes

X-liked disorders - colour blindness and haemophilia

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7
Q

what is a stem cell

A

an undifferentiated cell that can give rise to specialised cells and is capable of unlimited division

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8
Q

what is a totipotent cell

A

a cell that has the ability to differentiate into any and all cells of an organism, it is the least differentiated cell type eg. embryonic stem cell

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9
Q

what is a pluripotent cell

A

a cell with the ability to differentiate into most of the cells in an organism; some differentiation options may no longer be available because it has already started along the cell specialisation pathway
eg. bone marrow

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10
Q

how do stem cells become specialised

A
  • stimuli activate and inactivate certain genes
  • mRNA is only transcribed from active genes
  • this mRNA is then translated into proteins
  • these proteins modify the cell and determine structure and function
  • the changes that these proteins cause are what makes the cell increasingly specialised
  • the changes are difficult to reversible so specialisation/differentiation is irreversible
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11
Q

how can gene expression be controlled

A

by altering the rate of transcription in genes which is done by transcription factors; activators and repressors

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12
Q

what is an operon

A

a functioning section of DNA that contains a cluster of structural genes that get transcribed together, control elements, and sometimes a regulatory gene

structural genes - code for useful proteins eg. enzymes

control elements - includes a promoter and an operator

regulatory gene - codes for an activator or repressor

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13
Q

what is a promoter

A

the section of DNA where transcription starts

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14
Q

what is a terminator

A

the DNA section where transcription ends

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15
Q

what is a transcription factor

A

a molecule that regulates transcription rate

activator - increases transcription rate by helping RNA polymerase to bind to the DNA at the start of a gene so that transcription starts

repressor - decreases transcription rate by preventing RNA from binding to DNA at the start of a gene so that transcription occurs

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16
Q

what is the lac operon

A

it is found in E.coli bc E.coli usually respires with glucose but can use lactose
the lac operon carries the genes that produce the necessary enzymes to respire lactose

it has 3 structural genes; lacZ, lacY and lacA, these produce proteins that help bacteria to digest lactose, including beta-galactosidase and lactose permease

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17
Q

how does the lac operon work when lactose isn’t present vs is present

A

lactose not present:
the lac repressor is produced by the regulatory gene, the repressor binds to the operator site
- transcription of lactase is blocked because RNA polymerase now can’t bind to the promoter

lactose present:
lactose binds to the repressor to change the repressor’s shape, making it unable to bind to the operator site
RNA polymerase will now be able to begin the structural gene transcription and produce lactase

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18
Q

how are cells organised

A

cells have proteins on their surface called adhesion molecules, which help them locate and stick to ‘like minded’ cells

similar specialised cells –> tissue

tissues –> organ

organs –> organ system

organ systems –> organism

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19
Q

how can stem cells be used in treatment

A

they could be used to repair damaged nerve tissue in spinal cord injuries

they could be used to repair damaged heart tissue for heart disease/heart attack caused damage

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20
Q

what are adult stem cells and how are they obtained

A

they’re obtained from an adults body tissues, eg. bone marrow

relatively simple operation to obtain with very little risk but a lot of discomfort
donor is anaesthetised and a needle is inserted into the centre of a bone to remove a small quantity of bone marrow

they aren’t as flexible as embryonic stem cells, there’s a limited number of differentiation options

a patient can use their own adult stem cells if they need a stem cell transplant and there’s no rejection risk

21
Q

how do you get embryonic stem cells

A

obtained from early embryos
embryos are created in lab, using IVF where egg cells are fertilised by sperm outside the womb

after the embryos are 4 to 5 days old, stem cells are removed and the embryo remaining is then destroyed

they can develop into all specialised cell types

22
Q

what are some ethical ideas associated with embryonic stem cell use

A
  1. embryos can’t consent

many believe that at the moment of fertilisation, a genetically unique individual is formed that has the right to life, so they believe embryo destruction is wrong

  1. some have less objections to obtaining stem cells from an egg cell that hasn’t yet been fertilised by sperm, but has been activated artficially to start dividing; this is because these cells can’t survive more than a few days and wouldn’t form a fetus if placed in a womb
  2. some people think that scientists should only use adult stem cells because they don’t destroy embryos but they can’t specialise into as many cells
23
Q

what do regulatory authorities do

A

look at research proposals to decide if they should be allowed by considering ethical issues

involve licensing and monitoring centres in embryonic stem cell research to ensure that only fully trained staff carry the research out; helps avoid unregulated research

produce guidelines and codes of practice to ensures that all scientists are working in a similar manner and results can be compared

make sure they use controlled extraction methods and have a regulated max embryo stem cell usage age

monitoring developments in scientific research and advances to ensure that any field changes are appropriately regulated with up to date guidelines

providing info and advice to govs. and professionals to promote the science in embryo research and help society realise it’s importance

24
Q

genotype

A

the alleles that we inherit

25
Q

phenotype

A

the physical display of our inherited genotype

26
Q

recessive

A

a mutated disorder for which the genotype must be homozygous to display the phenotype

27
Q

dominant

A

a characteristic that is coded for and overrides the other allele for that trait

28
Q

co-dominance

A

when two dominant alleles are expressed in a phenotype

29
Q

allele

A

a variation of a gene

30
Q

what is polygenic inheritance

A

when one trait showing continuous variation is influenced by multiple genes found at various loci

31
Q

what is an epigenetic change

A

the influence of the environment on the genome without changing the DNA base sequence

32
Q

how is chromatin formed in eukaryotic cells

A

nuclear DNA wraps around proteins called histones to form chromatin

33
Q

how is gene expression altered through epigenetics

A
  1. methylation of DNA (adding -CH3 groups)
  2. histone modification (via acetylation of amino acids)

both can occur in different areas of the same DNA

34
Q

what can cause epigenetic changes

A

smoking/stress/exercise/diet/internal signalling from the body’s own cells

35
Q

what is DNA methylation

A

an epigenetic tag that acts as a repressor and prevents gene expression
a methyl group is added to the DNA, making the DNA less accessible to transcription factors/preventing them from binding as the chromatin becomes more condensed

36
Q

define tissue

A

the same specialised cell type grouped together to form a tissue

37
Q

what is an organ

A

made up of many types of tissues that work together to carry out an overall function

38
Q

define organ system

A

a group of organs with related functions, grouped together

39
Q

define the term sex-linked disorder

A

a disorder caused by a mutated gene on the X or Y chromosome, making it more likely to occur in one gender than the other

40
Q

can you reject your own stem cells

A

no, there’s no chance of rejection and immunosuppressant drugs don’t have to be taken

41
Q

autosomal

A

any chromosomes that aren’t the sex chromosomes

42
Q

what is histone acetylation

A
  1. acetylated histones have less condenses chromatin, so the proteins involved in transcription can bind to the DNA, allowing genes to be transcribed and so, activated
  2. removing acetyl groups from histones causes the chromatin to become highly condensed, the genes in the DNA can then not be transcribed as transcription proteins can’t bind to them, repressing genes
43
Q

outline a transmission electron microscope (TEM)

A

electromagnets are used to focus a beam of electrons which is then transmitted through the specimen
more electrons are absorbed by denser areas, making them darker in the image

+ high resolution images, you can see internal structures of organelles like mitochondria
– can only be used on thin specimens

44
Q

outline scanning electron microscopes (SEM)

A

SEM’s scan an electron beam across the specimen, knocking off electrons from the specimen which are gathered in a cathode ray tube to form an image
the images show the surface of the specimen and can be 3D

+ can be used on thick specimens
– lower resolution images then TEM’s

45
Q

explain how epigenetic changes affect development

A

DNA is wrapped around histones and methylation affects gene transcription, altering gene expression

46
Q

how could a hormone cause epigenetic changes

A

add methyl groups to DNA, modification of histones and therefore altering gene expression

47
Q

can epigenetic changes be passed on

A

yes they can get passed on and the genes that were de/activated in the original cell would be the same in the daughter cells

if the epigenetic change occurred due to a change in environment the daughter cells will be equipped to deal with the changed environment in the same way

48
Q

what are transcription factors

A

they bind to a DNA promoter sequence near the transcription start site and can be activators which increase transcription rate and help RNA polymerase to bind or repressors which do the opposite

49
Q

how do stem cells specialise

A

THEY DIFFERENTIATE
stimuli activate or inactivate etc.

a level biology (13 decks)

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