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Edexcel SNAB A Level Biology > Topic 3 - Voice of the Genome > Flashcards

Topic 3 - Voice of the Genome Flashcards

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1
Q

What is a eukaryotic cell?

A

A cell containing a nucleus and other membrane bound organelles

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2
Q

What is a prokaryotic cell?

A

A cell with circular DNA and no membrane bound organelles

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3
Q

What is the structure and function of the mitochondria?

A

Double membrane with the inner one folded to form cristae.
The mitochondria are the site of the later stages of aerobic respiration

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4
Q

What is the structure and function of the nucleus?

A

Double membrane (nuclear envelope) perforated by pores. Contains chromosomes and a nucleolus.
Acts as control centre of cell, retains genetic material and manufactures ribosomes

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5
Q

What is the structure and function of the nucleolus?

A

Dense body in nucleus
Makes rRNA and assembles ribosomes

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6
Q

What is the structure and function of a chloroplast? (PLANT CELL ONLY)

A

Double membrane, filled with grana (disc like stacks of thykaloids). Stroma
Carry out photosynthesis

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7
Q

What is the structure and function of the rough endoplasmic reticulum?

A

System of interconnected membrane-bound, flattened sacs with ribosomes attached to outer surface.
Protein synthesis

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8
Q

What is the structure and function of the smooth endoplasmic reticulum?

A

Same as rough ER but doesn’t have any attached ribosomes
Make lipids and steroids

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9
Q

What is the structure and function of a ribosome?

A

Made of RNA and protein - 2 different subunits
Site of protein synthesis

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10
Q

What is the structure and function of the Golgi apparatus?

A

Stacks of flattened, membrane-bound sacs formed by fusion of vesicles from ER. Curved/flattened cisternae of different sizes
Modifies proteins and packages them in vesicles for transport

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11
Q

What is the structure and function of a lysosome?

A

Spherical sac containing digestive enzymes, bound by a single membrane
Involved in breakdown of unwanted structures within cell, and sometimes in destruction of whole cells when old cells are to be replaced or during development

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12
Q

What is the structure and function of the cell surface membrane?

A

Phospholipid bilayer containing proteins and other molecules
Forms a partially permeable barrier

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13
Q

What is the structure and function of a centrosome?

A

A centrosome is composed of 2 centrioles
It duplicates before mitotic division and moves to opposite poles to start the process of spindle formation

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14
Q

What is the structure and function of a centriole? (ANIMAL CELL ONLY)

A

Hollow cylinders made up of a ring of 9 protein microtubules
Involved in formation of spindle during nuclear division

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15
Q

What is the structure and function of the cell wall? (PLANT CELL ONLY)

A

Outer protective layer composed of a number of polysaccharides
Provides mechanical strength to stop cell bursting, allows water to pass along it

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16
Q

What is the structure and function of a prokaryotic cell wall?

A

Made of peptidoglycan
Provides cells with support

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17
Q

What is the structure and function of the capsule (prokaryotic cells)?

A

Stick outermost layer usually composed of polysaccharides
Helps prokaryotes cling to each other

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18
Q

What is the structure and function of a plasmid?

A

A small circular double stranded DNA molecule
Carries DNA separate from chromosomal DNA

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19
Q

What is the structure and function of the pili?

A

Short hair like structure on cell surface
Involved in adherence to surfaces

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20
Q

What is the structure and function of a mesosome?

A

Invagination/infolding of plasma membrane
Used in aerobic respiration and cell wall formation

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21
Q

What is circular DNA?

A

DNA forming a closed loop with no ends

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22
Q

How are proteins made and modified? (GOLGI APPARATUS AND ER)

A

Transcription of DNA to mRNA in nucleus, then mRNA leaves nucleus.
Protein is made on the ribosomes of the Rough ER and then moves through the ER, gaining it’s 3D shape. It is then moved in a vesicle to fuse to form the flattened sacs of Golgi apparatus.
Here the proteins are modified, before being pinched off into vesicles and fused with the cell membrane to be released.

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23
Q

How is a glycoprotein created from a regular protein by the Golgi Apparatus?

A

The protein arrives and is modified by adding a carbohydrate to become a glycoprotein

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24
Q

What is the equation for magnification?

A

Magnification = size of image/size of object

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25
Q

What is the difference between resolution and magnification?

A

Resolution is the ability to distinguish between 2 points, whereas magnification is how enlarged an image is compared to a specimen

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26
Q

What is an eyepiece graticule and stage micrometer?

A

Eyepiece graticule = small engraved disc with an eyepiece ruler placed into eyepiece of microscope
Stage micrometer = used to calibrate the eyepiece graticule to work out the size of each graticule unit

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27
Q

What is the difference between a light and electron microscope?

A

Light - uses light to form image, much lower resolution and magnification
Electron - uses electrons to form an image, much higher resolution and magnification

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28
Q

How do you prepare a microscopic slide?

A

Liquid sample - add a few drops to slide and cover with coverslip
Solid sample - cut a thin layer of tissue cells from the sample, apply a stain to make cells more visible and cover with a coverslip

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29
Q

What are the common stains, what do they colour?

A

Methylene blue - stains animal cell nuclei blue
Iodine - stains starch-containing material in plant cells blue-black
Toluidine blue - stains tissues that contain DNA and RNA blue
Phloroglucinol - stains lignin found in some plant cells red/pink

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30
Q

What is a Transmission Electron Microscope, and what type of specimens can it be used on?

A

Uses electromagnets to focus a beam of electrons which is then transmitted through the specimen - has a very high resolution
Can only be used on thin specimens
Produces 2D images

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31
Q

What is a Scanning Electron microscope, and what type of specimen can it be used on?

A

Uses a beam of electrons to knock electrons off the specimen. Can be used on thick specimens, but gives lower resolution
Produces 3D images

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32
Q

What are gametes?

A

Sex cells

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33
Q

What are the adaptations of a sperm cell?

A

Acrosome - contains digestive enzymes to hydrolyse the zona pellucida
Flagellum - propels the sperm forwards (motility)
Large amounts of mitochondria - provide ATP for respiration, energy for swimming
Haploid - sexual reproduction
Hydrodynamic

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34
Q

What is the acrosome reaction?

A

When the acrosome in the head of the sperm swells, fuses with the head of the cell surface membrane and releases digestive enzymes. This then hydrolyses the zona pellucida

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35
Q

What are the adaptations of an egg cell?

A

Zona pellucida hardens after fertilisation to prevent polyspermy
Follicle cells provide protective coating
Cytoplasm contains nutrients for the embryo

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36
Q

What happens when the sperm and egg nuclei meet each other?

A

Egg nuclear envelope breaks down and the 2 haploid nuclei fuse, which produces a fertilised egg (zygote - diploid)

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37
Q

How do the events following the acrosome reaction prevent more than 1 sperm fertilising an egg?

A
  • sperm cell fuses with cell membrane
  • cortical granules are released by ovum via exocytosis
  • cortical granules released into the zona pellucida
  • this causes the zona pellucida to harden, preventing polyspermy
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38
Q

What are the similarities and differences between the acrosome and cortical reaction?

A

Similarities = both involve exocytosis, both involve vesicles
Differences = acrosome digests zona pellucida, cortical hardens it

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39
Q

What is meiosis?

A

A type of cell division that produces gametes

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40
Q

How does meiosis ensure genetic variation?

A
  • through the production of non-identical gametes
  • as a consequence of independent assortment of chromosomes and crossing over of alleles between chromatids
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41
Q

Explain how meiosis gives rise to genetic variation in gametes?

A

Independent assortment gives rise to different/new combinations of chromosomes
Crossing over means sections of chromosomes are swapped over

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42
Q

What is crossing over and how does it create genetic variation?

A

When sections of DNA are exchanged between non sister chromatids (chiasmata)
This gives rise to a large amount of genetic variation

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43
Q

What is independent assortment and how does it create genetic variation?

A

When chromosomes line up randomly on the cell equator during mitsosis
This means either chromosome from each pair could be in any gamete

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44
Q

What happens during meiosis?

A

Original cell - diploid
Before Meiosis I, chromosomes replicate. During Meiosis I, the homologous pairs of chromosomes are split up (still remain as 2 chromatids) to produce 2 haploid nuclei.
During Meiosis II, the chromatid pairs are pulled apart to produce 4 haploid nuclei (each chromosome is a single chromatid)

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45
Q

What is the locus of a gene?

A

The position of a gene on a chromosome

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46
Q

What is autosomal linkage?

A

When genes that are on the same autosome are not assorted independently (as they have a similar locus) so they become linked and stay together during original parental combination - meaning they are passed on to offspring all together.

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47
Q

What is the autosome?

A

All chromosomes except from the sex chromosomes

48
Q

What sex chromosomes do females have?

A

XX

49
Q

What sex chromosomes do males have?

A

XY

50
Q

Why is colour blindness more common in males than females?

A

Colour blindness is caused by a recessive allele on the X chromosome
Males only need 1 recessive allele to be colour blind whereas females need 2

51
Q

Why does males only having one X chromosome make it more likely they will inherit sex linked conditions?

A

Because it means they are hemizygous for any genes present on the X chromosome and therefore it will be expressed even if it is a recessive allele

52
Q

What is sex linkage?

A

When genes are linked due to the locus of the allele that the gene codes for being found on a sex chromosome

53
Q

What are the 3 stages of the cell cycle?

A

Interphase
Nuclear division (mitosis)
Cell Division (cytokinesis)

54
Q

What are the 3 phases in interphase?

A

G1
S
G2

55
Q

What happens in each of the 3 interphase stages?

A

G1 = signal received to divide again, cells make DNA, enzymes and proteins for growth
S = DNA replicates
G2 = cell continues to grow, new DNA checked, preparations for cell divison

56
Q

What happens to cell growth in mitosis?

A

It stops

57
Q

What happens in cytokinesis?

A

The whole cell divides to create 2 genetically identical daughter cells

58
Q

What is mitosis?

A

The process of nuclear division forming 2 genetically identical daughter nuclei (which are also identical to the parent nuclei)

59
Q

What happens during prophase?

A

Chromosomes condense, centrosomes move to opposite ends of the cell and spindle fibres begin to form. Nuclear envelope and nucleolus break down

60
Q

What happens during metaphase?

A

Centrosomes reach opposite poles, spindle fibres start to extend and attach to centromeres of chromosomes which are lined up on equator

61
Q

What happens during anaphase?

A

Sister chromatids separate at the centromere and are pulled away by shortening spindle fibres (microtubules) to opposite poles

62
Q

What happens during telophase?

A

Chromosomes arrive at opposite poles and start to decondense. Nuclear envelope reforms around each set of chromosomes, remainder of spindle breaks down

63
Q

Why is mitosis biologically significant?

A
  • for the growth of multicellular organisms from unicellular zygotes
  • replacement of cells and repair of tissue (cells are constantly dying so need to be replace by genetically identical cells)
  • asexual reproduction
64
Q

What is a stem cell?

A

An undifferentiated stem cell that can give rise to specialised cells and divide to produce more stem cells

65
Q

What is potency?

A

The ability to differentiate into more specialised cell types

66
Q

What are totipotent stem cells?

A

Stem cells that can differentiate into any cell type

67
Q

What are pluripotent stem cells?

A

Embryonic stem cells that can differentiate into any cell type found in an embryo, but not the cells forming placenta and umbilical cord

68
Q

What are multipotent stem cells?

A

Adult stem cells which have lost some of the potency associated with the embryonic stem cells, no longer pluripotent

69
Q

What are the differences between totipotent and pluripotent stem cells?

A
  • totipotent can differentiate into any cell type
  • pluripotent can only give rise to most (not all cells in the body or totipotent cells)
  • totipotent can give rise to an entire human, pluripotent cannot
70
Q

What are the uses of embryonic stem cells, and where are they taken from?

A

Huge potential in development of therapeutic treatments of diseases
Taken from embryos, and can therefore be pluri or totipotent

71
Q

What are the uses of adult stem cells, and where are they taken from?

A

Can be injected into damaged tissue to treat diseases such as leukaemia and also injuries - but must match blood type and antigen or there is a risk of rejection
Taken from bone marrow and brain

72
Q

How do official regulatory authorities make decisions about the use of stem cells?

A
  • review proposals for stem cell resarch
  • licensing and monitoring of research centres
  • providing guidelines and codes for practice
  • monitoring new developments
  • providing governments and other professional bodies with correct and up to date advice and info on stem cell research
73
Q

What are the benefits of stem cells?

A

Potential to treat a range of diseases, can develop treatments from a patient’s own organs, adult stem cells are already successful

74
Q

What are the risks/issues with stem cells?

A

Stem cells could become infected in lab, can develop into cancer cells due to mutations, there are low numbers of donors

75
Q

What are the social issues associated with the use of stem cells?

A

Lack of peer reviewed evidence to suggest success of stem cells, public must be educated sufficiently, embryonic stem cells collected before birth are expensive

76
Q

What are the ethical objections to the use of stem cells?

A

Amounts to killing an unborn child/abortion/murder, intefering in nature, may have genetic consequences for future generations, pressure to harvest human eggs for medical use, money could be used for other types of research

77
Q

What are the advantages of using stem cells from a patient rather than a donor?

A

Genetically identical cells to the patient therefore there is no risk of rejection.
No need to take immunosuppressant drugs, and less risk of infection

78
Q

How do cells become specialised?

A

Stimulus (e.g. chemical) causes some genes to be switched on/expressed. This leads to transcription of active genes, the mRNA produced is then translate to create the protein. This protein modifies the cell/determines cell structure

79
Q

What is a transcription factor?

A

A protein that controls the transcription of genes by binding to a specific region of DNA

80
Q

What are the 2 types of transcription factor?

A

Transcription factors increasing rate of transcription = activators
Transcription factors decreasing rate of transcription = repressors

81
Q

How do transcription factors control gene transcription?

A

Binding to promotor region of a gene
They interact with RNA polymerase, either assisting or preventing it

82
Q

What is an operon?

A

A group or cluster of genes that are controlled by the same promoter

83
Q

What is the lac operon?

A

Section of genes that controls production of enzyme lactase, which is ‘inducible’ and only synthesised when lactose is present

84
Q

What happens when lactose is absent? (lac operon)

A
  • regulatory gene is transcribed and translated to produce the lac repressor protein
  • the protein binds to the operator region
  • due to the presence of the promoter region, RNA polymerase is unable to bind
    NO LACTASE PRODUCED
85
Q

What happens when lactose is present? (lac operon)

A
  • lactose is present so binds to lac repressor protein and distorts it
  • this means it can no longer bind to the operator region
  • RNA polymerase is able to bind to the promoter region
    LACTASE IS PRODUCED
86
Q

What is an organelle?

A

A component within a cell that carries out a specific task

87
Q

What is a cell?

A

The basic functional and structure unit within a living organism

88
Q

What is a tissue?

A

A group of cells that works together to perform a particular function

89
Q

What is an organ?

A

Made from a group of different tissues working together to perform a particular function

90
Q

What is an organ system?

A

Made from a group of organs with related functions, working together to perform body functions within the organism

91
Q

What is phenotype?

A

The observable characteristics of an organism

92
Q

What is phenotype determined by?

A

The expression of an organism’s genotype and it’s interaction with it’s environment

93
Q

What is genetic variation?

A

The small differences in DNA base sequence between individual organisms within a species

94
Q

Why is the variation in phenotype due to genetics inherited but the variation in phenotype due to environmental factors not?

A

Genetic variation directly affects the DNA of the gametes but variation in the phenotype caused by the environment does not

95
Q

What does monogenic mean?

A

Characteristics controlled by one gene

96
Q

What does polygenic mean?

A

Characteristics controlled by several genes

97
Q

What is polygenetic inheritance?

A

When a single characteristic is coded for by several genes at different loci. Gives rise to continuous variation

98
Q

What in the genotype can determine the phenotype?

A

The different alleles an organism has at a single gene locus can determine the phenotype

99
Q

What are environmental factors that can affect the phenotype of plants?

A

Living conditions:
- availability of water
- supply of nutrients
- temperature range
- oxygen levels
- length of sunlight hours

100
Q

How do changes in environmental factors affect changes in the phenotype of an organism?

A

Because environmental factors change how an organism grows and develops
Environmental factors determine the achievement of the genetic potential

101
Q

How can the height of an adult human demonstrate how environmental factors interact with genotype (diet)?

A

Malnutrition - prevents a nutrient being taken in for specific growth - e.g. bone growth/muscle growth
Other environmental factors can determine expression of genotype (such as health)
Environmental factors determine the achievement of genetic potential

102
Q

What are the features of discontinuous variation, and what type of variation in the phenotype gives rise to it?

A

Generally monogenic inheritance causing qualitative differences
Features:
- distinct classes/categories
- characteristics cannot be measured over a range
- individuals cannot have features that fall in between categories

103
Q

What are the features of continuous variation, and what type of variation in the phenotype gives rise to it?

A

Caused by multiple different genes or multiple alleles for the same gene at many different loci as well as the environment (polygenic inheritance causing quantitative differences)
Features:
- no distinct classes or categories
- characteristics can be measured and fall within a range between 2 extremes

104
Q

What is epigenetics?

A

The control of gene expression by factors other than an individual’s DNA sequence. This involves switching genes on and off withou changing the actual code

105
Q

What are histones?

A

Proteins around which nuclear DNA is wrapped to form chromatin

106
Q

How can chromatin be chemically modified to alter gene expression?

A
  • methylation of DNA
  • histone modification via acetylation of amino acid tails
107
Q

What is DNA methylation and what change does it cause?

A

The direct addition of methyl groups (CH3) to DNA
Causes the inactivation of genes

108
Q

How does DNA methylation cause the inactivation of genes?

A

Methylation suppresses the transcription of the affected gene by inhibiting binding of transcription factors and the enzymes needed for transcription

109
Q

What can DNA methylation be affected by?

A

Environmental, lifestyle or age related factors

110
Q

What is the acetylation of histones and what change does it cause?

A

The addition of acetyl groups (-COCH3) to lysine amino acids on histone proteins
It causes genes to be activated

111
Q

How does histone acetylation cause gene expression?

A

On lysine amino acid, there is normally a positively charged R group which forms iocnic bonds with the phosphate backbone - so DNA coils tightly.
Adding an acetyl group removes the positive ion, removing a bond between the histone protein and DNA so it becomes less tightly wrapped.
Less tightly wrapped DNA means RNA polymerase and transcription factors can bind more easily and the gene is activated

112
Q

Can epigenetic changes be passed on?

A

Yes, via cell divison
EXAMPLE - during gamete production, DNA in parent cells usually undergoes de-methylation, but often methyl groups are not removed and therefore are present in DNA on sperm or egg cells
Epigenetic changes due to environmental factors therefore can be passed down to the next generation

113
Q

Why does increasing the number of stem cell divisions increase the risk for cancer?

A

Greater number of cell divisions = more opportunities for errors in DNA replication
Therefore more mutations may occur, creating a greater chance of cancer.

114
Q

What are the comparisons/contrasts between the acrosome and cortical reaction?

A

SAME: both involve vesicles, both involve release of a substance via exocytosis
DIFFERENT: acrosome causes digestion of zona pellucida, cortical causes thickening of zona pellucida

115
Q

What is molecular phylogeny?

A

Study of molecular differences/similarities in DNA/RNA and proteins to determine evolutionary relationships between organisms

Edexcel SNAB A Level Biology (9 decks)

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