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A Level Biology Edexcel A > The Voice of the Genome > Flashcards

The Voice of the Genome Flashcards

Topic 3

1
Q

State 3 structural differences between a prokaryotic cell and a eukaryotic cell.

A
  1. Prokaryotes have no membrane bound organelles whereas eukaryotes do have membrane bound organelles. e.g. mitochondria.
  2. Prokaryotes have DNA in cytoplasm whereas eukaryotes have DNA in cell nucleus.
  3. Prokaryotes have 70s small ribosomes whereas eukaryotes have 80s large ribosomes.
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2
Q

Describe the structure and function of the capsule.

A

Structure: thick, slimy layer of polysaccharide that covers the cell wall.
Function: prevents cell from dying out, helps adhesion to surfaces.

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3
Q

Describe the structure and function of a prokaryotic cell wall.

A

Structure: forms a rigid outer layer, made of peptidoglycan.
Function: provides strength, support, protection against damage.

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4
Q

Describe the structure and function of a plasmid.

A

Structure: circular molecules of DNA.
Function: DNA replication, gene expression, can contain genes for antibiotic resistance and can be transferred between prokaryotes.

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5
Q

Describe the structure and function of the flagellum.

A

Structure: a long, thin tail like projection attached to the cell wall.
Function: movement, propels the cell forward using a corkscrew motion.

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6
Q

Describe the structure and function of the pili.

A

Structure: short hair-like extensions.
Function: help cells to adhere to surfaces, primarily each other for transfer of genetic material.

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7
Q

Describe the structure and function of the mesosomes.

A

Structure: inward folds of the plasma membrane.
Function: ATP production (respiration).

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8
Q

Describe protein transport.

A
  1. Amino acids are joined together to form a polypeptide chain on a ribosome attached to the rough ER
  2. The polypeptide passes through the cisternae membrane and into the lumen of the rough ER where the polypeptide folds into its 3D shape (protein).
  3. ER packages proteins into ER vesicles which transport the protein to Golgi apparatus/body
  4. ER vesicles fuse with Golgi apparatus membrane to become part of the Golgi apparatus
  5. Protein enters the Golgi body and is modified as the protein moves through the Golgi body
  6. The proteins (eg. enzymes) are packaged into a Golgi secretory vesicle for transport through the cell cytoplasm
  7. This vesicle moves to the cell surface membrane , fuses with it and the proteins (eg. enzymes) exit the cell by the process of exocytosis
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9
Q

Define extracellular enzyme.

A

Biological protein/ enzyme made by a cell/ organism. A biological catalyst which speeds up a chemical reaction by lowering the activation energy.

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10
Q

Describe the purpose of the acrosome reaction.

A

To digest the zone pellucida to allow the sperm to enter the ovum.

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11
Q

Describe the purpose of the cortical reaction.

A

To thicken and harden the zona pellucida of ovum to prevent polyspermy.

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12
Q

Describe the acrosome reaction.

A
  1. The ovum releases chemicals/chemokines which attract sperm
  2. Receptors on the head of the sperm binds to the zona pellucida of the ovum
  3. The acrosome in the head of the sperm swells , then the acrosome membrane fuses with the sperm cell membrane
  4. Hydrolytic/digestive enzymes are released from the acrosome by exocytosis
  5. The zona pellucida of the egg is hydrolysed / digested by the enzymes, allowing the sperm head to reach, bind to and fuse with the ovum membrane. Genetic material in the nucleus of one sperm passes through the ovum cell membrane and enters the ovum
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13
Q

Describe the cortical reaction.

A
  1. Genetic material from the sperm head enters the ovum
  2. Cortical granules in the cytoplasm of the ovum move towards and fuse with egg cell surface membrane, releasing enzymes by exocytosis into the zona pellucida
  3. The zona pellucida hardens/ thickens which prevents polyspermy
  4. There is a change in charge across egg cell membrane.
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14
Q

Define fertilisation.

A

The fusion of the nuclei from the sperm cell (male gamete) and ovum (female gamete).

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15
Q

Define haploid.

A

Half the number of chromosomes found in a somatic cell.

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16
Q

Define diploid.

A

Full number of chromosomes found in a somatic cells.
Two copies of each chromosome

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17
Q

How many chromosomes does a somatic cell have?

A

46 chromosomes.

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18
Q

How many pairs of chromosomes do humans have?

A

23 pairs

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19
Q

Give the two roles of meiosis.

A
  1. It results in haploid nuclei necessary to maintain the diploid number of chromosomes after fertilisation.
  2. Creates genetic variation in offspring.
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20
Q

Define stem cell.

A

An undifferentiated cell that can can give rise to other specialised cell types. No hayflick limit. Can be totipotent, pluripotent or multipotent.

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21
Q

Give the 3 types of stem cells.

A

Totipotent
Pluripotent
Multipotent

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22
Q

Define Totipotency.

A

When an undifferentiated stem cell can give rise to all specialised cell types. No limit to division. All genes switched on.

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23
Q

Define Pluripotency.

A

When an undifferentiated stem cell can give rise to most specialised cell types except totipotent embryonic stem cells. No limit to division. Some genes switched off.

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24
Q

Define Multipotency.

A

When an undifferentiated stem cell can give rise to only specialised cell types of a closely related family. Many genes switched off.

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25
Define cell.
The basic unit from which living organisms are built. Can be specialised for a particular function.
26
Define tissue.
A group of one type of cells (often have the same origin - specialised) which work together to carry out a specific function/s. e.g muscle tissue.
27
Define organ.
A group of different tissues which work together to carry out one or more functions. e.g. heart.
28
Define organ system.
A group of different organs working together for the same function. e.g. digestive system.
29
What is formed when there are multiple organ systems working together?
Multicellular organism.
30
Define apoptosis.
Programmed cell death - the process in which healthy animal cells die during the normal development of an organism, in particular places e.g between the fingers.
31
How are master genes involved in early development of an organism?
Master genes control the development of segments of an organism. e.g legs. The master genes produce mRNA that is translated into signal proteins. These proteins switch on the genes responsible for producing the proteins needed for specialisation of cells in each segment.
32
Explain how cell form tissues (cell recognition).
Similar specialised cells recognise each other using adhesion/ recognition molecules (proteins or glycoproteins) found on the cell surface membrane. These molecules have complementary shapes and can bind to each other through the tissue fluid surrounding the cells. The cells form a tissue.
33
Define variation.
The differences that exist between individuals.
34
What is variation in phenotype caused by?
Genotype and environment.
35
Define polygenic inheritance.
A single characteristic showing continuous variation caused by multiple genes at different loci.
36
What does a dihybrid cross show?
The inheritance of two characteristics (two genes at different loci).
37
How do cells become specialised? (differential gene expression)
The correct stimulus e.g hormone causes some genes to be activated (switched on) and some to be de-activated. The activated genes are transcribed producing mRNA, which is then translated to produce proteins. These proteins determine the structure and function of cells as different proteins permanently modify a cell in different ways.
38
How does DNA methylation affect gene transcription?
Involves addition of methyl group to one of the bases. Prevents transcription factors from binding. Therefore gene transcription is suppressed.
39
Describe the two types of phenotypic variation.
Continuous = variation exists as gradual changes over a range. e.g. height. Discontinuous = variation exists as distinct categories. e.g. blood group.
40
What is a locus?
The fixed position/ location of a gene/ allele on a chromosome.
41
Describe linked genes.
Linked genes are found on the same chromosome, but at different gene loci. They have a high chance of being inherited together, as when the chromatids separate in meiosis II all the genes on the chromatid move as one unit and enter the same gamete.
42
Define sex-linked gene.
An allele or gene responsible for a trait is located on a sex X/Y chromosome.
43
What are autosomal chromosomes?
Chromosomes that are not sex chromosomes.
44
Give two examples of sex-linked conditions.
-Colour blindness -Haemophilia
45
Define multifactorial disease.
Many factors contribute to the risk of developing the disease.
46
What is cancer?
Cancer is a disease resulting from uncontrolled cell division which forms a malignant tumour (a mass of abnormal, unspecialised cells), which invades and destroys surrounding tissue.
47
Is meiosis cell division or nuclear division?
Nuclear division
48
How many divisions are there in meiosis?
2
49
Describe the process of meiosis.
1. Homologous chromosomes line up in pairs down the equator of cell. 2. Meiosis I - homologous chromsomes seperate from each other, as the spindle fibres contract. 3. Meisosis II - sister chromatids seperate from each other, producing 4 gametes.
50
How does meiosis create genetic variation?
1. Independent Assortment of maternal and paternal chromosomes. 2. Crossing Over between non-sister chromatids of homologous chromosomes. This forms new combinations of alleles in the gametes.
51
Describe independent assortment.
Maternal and paternal chromosomes randomly align in different combinations along the equator of the cell.
52
Describe crossing over.
At the chiasmata, the chromatids break and rejoin, exchanging sections of DNA. Forms recombinants (chromosomes that contain new allele combinations from both parents).
53
Explain what is meant by the term sex-linked disorder.
A disorder caused by a mutated/ faulty gene located on the X/Y chromosome. Therefore the disorder is more likely in one gender than another.
54
Explain how crossing over may differ in sex-chromosomes.
-Cross overs cannot form between the sex X/Y chromosomes. -because they are not homologous chromosomes/ the Y chromosome is shorter.
55
Explain the role/ uses of mitosis.
Produces genetically identical cells which are needed in growth, repair and (in prokaryotes) asexual reproduction.
56
Explain why DNA is replicated before mitosis begins.
-To ensure that there is diploid number of chromosomes/ one copy of each chromosome in each daughter cell. -To ensure the daughter cells are genetically identical.
57
How does histone modification affect gene expression?
DNA in a chromosome is wrapped around histone proteins. Acetylation/ modification of histone affects binding of RNA polymerase/ chromosome unwinding.
58
State the 4 stages of mitosis.
Prophase Metaphase Anaphase Telophase
59
Describe the events that occur during prophase in an animal cell.
Chromosomes condense (visible). Centrioles move to opposite poles of the cell. Spindle fibres form, ready for the centromeres to attach to. Nucleolus and nuclear envelope break down.
60
Describe the events that occur during metaphase in an animal cell.
Centromeres of sister chromatids attach to spindle fibres and chromosomes line up down the equator of the cell.
61
Describe the events that occur during anaphase in an animal cell.
Centromeres split, separating the two sister chromatids. Spindle fibres shorten and contract, pulling the two chromatids to opposite poles of the cell.
62
Describe the events that occur during telophase in an animal cell.
Chromosomes decondense, nuclear envelope forms around each cluster of chromosomes, two nuclei form, spindle fibres break down.
63
Define epigenetic modification.
Changes that affect gene expression/ activation but do not change the base sequence of DNA.
64
What is the importance of the large size of the ovum?
Many sperm able to fit round it, so increased chance of fertilisation. Contains more lipid droplets, so more energy for developing embryo.
65
What is the function of the zona pellucida?
Hardens when one sperm has entered to prevent polyspermy.
66
What are cortical granules?
Lysosomes that release enzymes which cause the zona pellucida to harden to prevent polyspermy.
67
What is the role of cytoplasm with proteins and lipid droplets in the ovum?
Food source to supply energy for cell division of the fertilised ovum, until implantation.
68
What is the significance of the haploid nucleus in the ovum?
Contains half the number of chromosomes, so that the diploid chromosome number is restored at fertilisation. Mixing of alleles allows for genetic variation.
69
What is the function of the flagellum in sperm?
Allows sperm to swim to reach the ovum (in the oviduct).
70
Why do sperm have many mitochondria?
Carry out aerobic respiration to release energy in the form of ATP so the tail can move and so the sperm can swim to the egg.
71
What is an acrosome?
A specialised lysosome which contains and releases digestive enzymes, which hydrolyse the zona pellucida, enabling the sperm to enter the ovum.
72
What is the significance of the haploid nucleus in sperm?
Same as ovum.

A Level Biology Edexcel A (9 decks)

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