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Edexcel A Biology > TOPIC 3 > Flashcards

TOPIC 3 Flashcards

1
Q

What is a prokaryotic cell?

A

A prokaryotic cell is a cell which contains no nucleus and no membrane- bound organelles.

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2
Q

What is the function of the capsule on a prokaryotic cell?

A

It is a slime coat used for the protection of the cell and to prevent dehydration of the cell

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3
Q

What is the function of the pilli?

A

The pilli are thin protein tubes which allow bacteria to adhere to surfaces

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4
Q

What is a plasmid

A

A small circle of DNA

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5
Q

What is the function of the flagellum in a prokaryotic cell?

A

Hollow, thread like structure which rotates to move the cell

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6
Q

What is the ribosome the site of?

A

Protein synthesis

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7
Q

Is the DNA of prokaryotic cells associated with proteins?

A

No

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8
Q

Define a eukaryotic cell.

A

A eukaryotic cell is a cell with a nucleus and membrane bound organelles

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9
Q

What, in a eukaryotic cell, is either found free in the cytoplasm or attached to the ER?

A

Ribosomes

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10
Q

Where are ribosomes made in a eukaryotic cell?

A

Nucleolus, a dense body within the nucleus

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11
Q

What does the Smooth ER synthesise?

A

Lipids, steroids, reproductive hormones

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12
Q

What is the Golgi and what does it do?

A

Stacks of flattened, membrane-bound sacs formed by the fusion of vesicles from the ER. The Golgi modifies proteins, attaches carbohydrate molecules and packages them in vesicles for transport

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13
Q

What is the mitochondria the site of?

A

The later stages of aerobic respiration

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14
Q

What are the finger-like projections in the mitochondria?

A

cistae

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15
Q

What is a gene?

A

A sequence of bases in DNA which codes for a sequence amino acids which codes for a new protein/ polypeptide chain

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16
Q

What is a lysosome?

A

Spherical sacs containing digestive enzymes and bound by a single membrane.

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17
Q

The function of a lysosome is

A

to break down unwanted structures in the cell and to destruct whole cells when cell replacement occurs

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18
Q

What are centrioles? What is the function of centrioles?

A

Every animal cell has one pair of centrioles, which are hollow cylinders made up of microtubules. They are involved in the formation of the spindle during nuclear division and in transport within the cytoplasm.

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19
Q

What is the production of protein and their route through the cell?

A

1) Transcripted mRNA leaves nucleus
2) Proteins made on ribosomes enter rough ER
3) Protein moves through the ER assuming a 3-D shape en route- protein is processed
4) Vesicles pinched off the rough ER contain the protein
5) Vesicles from the rough ER fuse to form the Golgi apparatus sacs
6) Proteins are processed further and modified e.g. with the attachment of a carbohydrate molecule
7) Vesicles pinched off Golgi containing modified protein
8) Vesicle fuses with cell membrane, exocytosis

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20
Q

What is a Mammalian gamete?

A

A haploid sex cell produced via meiosis

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21
Q

What are the Mammalian gametes?

A

Sperm and Ovum

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22
Q

How is the ovum adapted for sexual reproduction?

A

1) haploid, so can fuse with the nuclei of the sperm to create a diploid zygote
2) has a cytoplasm with protein and lipid reserved for a developing embryo
3) a zona pellucida jelly surrounding layer which hardens in order to prevent multiple sperm from penetrating the egg (polyspermy)

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23
Q

How is the sperm cell adapted for its function?

A

1) long flagellum for swimming through the cervical tubes, motility
2) lots of Mitochondria in the middle to provide energy and respire for swimming
3) The sperm head is covered by an acrosome, a specialized structure that contains enzymes. The acrosomal enzymes help the sperm penetrate and dissolve the outer protective layers of the ovum, facilitating fertilization.
4) haploid, fuse with egg to create a zygote with the full set of chromosomes

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24
Q

Describe the acrosome reaction

A

1) Sperm reach the ovum
2) Chemicals are released from the ovum’s surrounding cells, triggering the reaction
3) The acrosome swells and fuses with the sperm cell surface membrane
4) Acrosomes release digestive enzymes which digest through the follicle cells and the Zona Pellucida
7) Sperm fuses with the ovum membrane

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25
Q

Describe the cortical reaction.

A

1) The sperm nucleus enters the ovum
2) Enzymes released from lysosomes in the ovum thickens the jelly like layer, preventing entry from other sperm
3) Nucleus of both gametes fuse to produce zygote

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26
Q

Describe the chain of meiosis

A

1) Chromosomes replicate before division- they are made up of two strands of genetic material, two chromatids
2) Meiosis 1- Homologous chromosomes pair up and separate
3) Chromatids separate and gametes are formed, each with half of the original chromosomes.

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27
Q

What is independent assortment

A

Independent assortment is a principle in meiosis that states that during the formation of gametes, the distribution of alleles for different traits is random and independent of one another. This means that the segregation of one pair of alleles (from one parent) during meiosis is independent of the segregation of another pair of alleles (from the other parent), resulting in a variety of possible combinations of traits in offspring.

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28
Q

Describe the process of crossing over.

A

During meiosis 1, homologous chromosomes come together as pairs and all four chromatids come into contact. At these points, the chromatids break and rejoin, exchanging sections of DNA between non-sister chromatids. These points are chiasmata and there are several along the lengths of each pair of chromosomes, giving rise to a large amount of variation.

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29
Q

Is there crossing over between the sex chromosomes during meiosis?

A

There isn’t.

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30
Q

What are the three phases of interphase?

A

G1, S1, G2

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31
Q

During PROPHASE…

A

the chromosomes shorten and thicken (condense) to be visible as two identical replicated chromatids (strands). They are joined at the centromere. Then, the spindle forms- and the centrioles move around the nuclear envelope and position themselves at opposite poles of the cell, followed by the spindle fibres forming between the poles. The nuclear envelope then breaks down.

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32
Q

In METAPHASE…

A

the chromosomes’ centromeres attach to the spindle fibres at the equator (widest part of the spindle).

33
Q

In ANAPHASE…

A

the centromeres split and the spindle fibres shorten and pull the halves of the centromere in each direction, toward the poles of the cell. The spindle proceeds to break down.

34
Q

In TELOPHASE…

A

the chromosomes unravel and the nuclear envelope reforms such that the two sets of genetic information are enclosed in separate nuclei.

35
Q

In cytoplasmic division…

A

the new cell surface membranes constricts around the centre of the cell.

36
Q

What happens in interphase?

A

G1
the cell grows in size, and performs its normal metabolic functions, such as protein synthesis and energy production. G1 phase is also a period of intense biochemical activity in which the cell prepares itself for DNA replication, which occurs during the next phase, S phase.
S1
During the S phase (Synthesis phase), the cell replicates its DNA in preparation for cell division.
G2
Synthesis of organelles
Protein synthesis
The centrosomes replicate and the spindle fibres assemble

37
Q

When do the chromosomes condense to become visible?

A

Prophase

38
Q

When do the chromatids line up in the middle of the cell?

A

Metaphase

39
Q

When does the spindle break down?

A

Anaphase

40
Q

In telophase, are the genetic material enclosed in two separate nuclei?

A

Yes

41
Q

What is the word for a stem cell that can give rise to any specialised cell, and even to an entire organism?

A

Totipotent stem cell

42
Q

What is a pluripotent stem cell?

A

A stem cell which can give rise to many different specialised cells, but not to an entire organism

43
Q

Which specialised cells can embryonic stem cells give rise to?

A

Only certain types of cells, not an entire organism

44
Q

What is a stem cell?

A

Stem cell = undifferentiated basic cells that have the potential to give rise into any specialised cell

45
Q

What is multipotency

A

Multipotency = adult stem cells that have the ability to form a variety of different cell types

46
Q

How do stem cells give rise to different specialised cells even though they have an identical genome to each other?

A

Despite the stem cells having the same genome, they are able to specialise into a diverse range of cell types because during differentiation certain genes are expressed (‘switched’ on)

47
Q

How does cell differentiation work?

A

Under certain conditions, some genes in a stem cell are activated, whilst others are inactivated
mRNA is transcribed from active genes only
This mRNA is then translated to form proteins
These proteins are responsible for modifying the cell (e.g. they help to determine the structure of the cell and the processes that occur within the cell)
As these proteins continue to modify the cell, the cell becomes increasingly specialised
The process of specialisation is irreversible (once differentiation has occurred, the cell remains in its specialised form)

48
Q

Define transcription factor.

A

a protein that controls the transcription of genes by binding to a specific region of DNA, they control gene expression

49
Q

What is an operon?

A

An operon is a section of DNA that includes:
A 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) and an operator region (where transcription factors bind)
Some operons may include regulatory genes that code for activators or repressors

50
Q

What is the lac operon? What is its purpose?

A

The lac operon controls the production of the enzyme lactase (also called β-galactosidase) and two other structural proteins

51
Q

What is the purpose of lactase?

A

Lactase breaks down the substrate lactose so that it can be used as an energy source in the bacterial cell

52
Q

What is the structure of the lac operon? What are its components?

A

The components of the lac operon are found in the following order:
Promoter for structural genes
Operator
Structural gene lacZ that codes for lactase
Structural gene lacY that codes for permease (allows lactose into the cell)
Structural gene lacA that codes for transacetylase
Located to the left (upstream) of the lac operon on the bacterium’s DNA there is also the:
Promoter for regulatory gene
Regulatory gene lacI that codes for the lac repressor protein

53
Q

The lac repressor protein has two binding sites. Where can it bind to?

A

The lac repressor protein has two binding sites that allow it to bind to the operator in the lac operon and also to lactose (the effector molecule)

54
Q

What happens when the lac repressor protein binds to the operon and the lactose?

A

When it binds to the operator it prevents the transcription of the structural genes as RNA polymerase cannot attach to the promoter
When it binds to lactose the shape of the repressor protein distorts and the repressor protein can no longer bind to the operator

55
Q

What happens when lactose is absent in the lac operon model?

A

The following processes take place when lactose is absent in the medium that the bacterium is growing in:
The regulatory gene is transcribed and translated to produce lac repressor protein
The lac repressor protein binds to the operator region upstream of lacZ
Due to the presence of the repressor protein RNA polymerase is unable to bind to the promoter region
Transcription of the structural genes does not take place
No lactase enzyme is synthesized

56
Q

What happens when lactose is present in the lac operon model?

A

There is an uptake of lactose by the bacterium
The lactose binds to the second binding site on the repressor protein, distorting its shape so that the repressor protein cannot bind to the operator region
RNA polymerase is then able to bind to the promoter region and transcription takes place
The mRNA from all three structural genes is translated
The enzyme lactase is produced and lactose can be broken down and used for energy by the bacterium

57
Q

What happens when lactose is present in the lac operon model?

A

There is an uptake of lactose by the bacterium
The lactose binds to the second binding site on the repressor protein, distorting its shape so that the repressor protein cannot bind to the operator region
RNA polymerase is then able to bind to the promoter region and transcription takes place
The mRNA from all three structural genes is translated
The enzyme lactase is produced and lactose can be broken down and used for energy by the bacterium

58
Q

The more differentiated a cell is…

A

The more potency it loses

59
Q

What are some ethical issues with the use of embryonic stem cells?

A

When does an embryo become a human w/ human rights?
Is it acceptable to use human embryos specially created for research?
Is it acceptable to remove the chance of life from the embryo in fused cells?

60
Q

What is gene expression?

A

the process by which information from a gene is used in the synthesis of a functional gene product

61
Q

The process of gene expression is…

A

Correct stimulus is given to unspecialised cells
Some genes are switched on and become active, others switched off
mRNA is made from the active genes only
mRNA goes to the ribosome to be read and protein is made
The protein can permanently alter the structure and function of the cells

62
Q

What is the definition of epigenetics?

A

the study of changes in organisms caused by modification of gene expression

63
Q

Describe the Acetabularia experiment.

A

Separate each section and see what grows, and what it grows into
The stem didn’t grow and the tip only grew a matching hat not a rhizoid
Cut the hat off, then the rhizoid later on and see what hat grows
A matching hat grew but the rhizoid did not grow back
Cut the rhizoid and hat off, and move the nucleus to the stem and see if/what grows
The matching hat and rhizoid grew back
Swap the stem and cut the hat off, and see what hat grows, then cut the hat off again
The first hat was an intermediate hat
The second hat matched the rhizoid
Shows that DNA is left in the stem, the rhizoid with the nucleus controls the growth of everything, the tip can only regrow a stem and hat from the DNA left in the tip

64
Q

Define epigenome

A

a mixture of chemical markers that ‘instruct’ genes/ are attached to histone proteins

It affects the phenotype w/o affecting genotype

65
Q

What is a tissue?
What is an organ?
What is an organ system?

A

A group of specialised cells working together to carry out one function
A group of tissues working together to carry out one function
A group of organs working together to carry out a particular function

66
Q

What is B-Galactosidase?

A

The enzyme in the lac operon model which breaks down lactose. It is transcribed by the DNA in the lac operon and a lac repressor molecule prevents its production.

67
Q

What happens when a methyl group is attached to the DNA of a gene?

A

This stops the RNA polyemerase from binding to the promoter

68
Q

Define histone modification

A

The binding of epigenetic markers to histone tails alters how tightly DNA winds around histone proteins

69
Q

When the DNA is wound tightly around the histone proteins, what does this do to the expression of the gene?

A

Deactivates it, prevents transcription into mRNA

70
Q

What is a locus?

A

a locus (plural = loci) is the location of genes on a chromosome.

71
Q

What is the phenotype?

A

outward expression of a cell or organism due to the interaction of:

Genotype:
Genetic differences leading to outward differences
Environment:
Environmental differences leading to outward differences

72
Q

What is a master gene?

A

The genes that control the development of a section of an organisms structure.

73
Q

What is discontinuous data?
What about continuous data?

A

1) Data that falls in discrete groups with no overlap
2) Data that falls within any value within certain range.

74
Q

Which two types of gene have a role in control of the cell cycle?

A

Oncogenes, Tumour suppressor genes

75
Q

Oncogenes are…

A

genes which code for proteins that stimulate the transition from one stage of the cell cycle to the next stage. Mutations/ less methylation can lead to the cell cycle being continuously active.

76
Q

Tumour suppressor genes are…

A

produce suppressor proteins which stop the cell cycle

77
Q

How does sex linkage work?

A

Some genes are only present on one sex chromosome and not the other
As the inheritance of these genes is dependent on the sex of the individual they are known as sex-linked genes
Most often sex-linked genes are found on the longer X chromosome
If the gene is on the X chromosome, males (XY) will only have one copy of the gene, whereas females (XX) will have two
Because males only have one X chromosome, they are much more likely to show sex-linked recessive conditions (such as red-green colour blindness and haemophilia)
Females, having two copies of the X chromosome, are likely to inherit one dominant allele that masks the effect of the recessive allele

78
Q

What is autosomal linkage?

A

As its name implies, autosomal linkage only occurs on the autosomes (any chromosome that isn’t a sex chromosome)
Two or more genes on the same autosome do not assort independently during meiosis
Instead, these genes are linked and they stay together in the original parental combination
These linked genes are passed on to offspring all together (through the gametes)

Edexcel A Biology (2 decks)

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