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A-level Biology > 3.1 - In the beginning > Flashcards

3.1 - In the beginning Flashcards

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1
Q

What are centrioles?

A

They are hollow cylinders made from 9 protein microtubules(polymers of globular proteins arranged in a helix to form a tube). They are involved in the formation of the spindle by organising the microtubules during nuclear division(mitosis) and in transport within the cell cytoplasm

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2
Q

What is the cytoplasm / function?

A

A fluid like substance found inside the cell that is mainly composed of water.
The cytoplasm acts as a site for chemical reactions.
The cytoplasm supports the shape of the cell.
The cytoplasm contains different cell structures within it.

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3
Q

What is the plasma membrane / function?

A

a biological membrane that separates the interior of a cell from its outside environment. It is a fluid mosaic of lipids, proteins and carbohydrate. The plasma membrane is impermeable to ions and most water-soluble molecules.

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4
Q

What is the nuclear envelope / function?

A

-The nuclear envelope contains the outer and inner membrane of the nucleus.
-Protects the genetic material inside the cell which could become damaged if it leaves the cell

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5
Q

What is the nuclear pore/function?

A

-Nuclear pores allow things to leave and enter the nucleus of the cell
-They allow mRNA to leave the cell for protein synthesis

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6
Q

What is the smooth endoplasmic reticulum (SER) ?

A

It is present in both animal and plant cells
The smooth endoplasmic reticulum is similar to the rough ER but it doesn’t have any ribosomes attached.
Smooth ER is mainly associated with lipid production, metabolism, steroid production and hormone production. It also has a detoxification function
Consists of tubules, which are located near the cell periphery
The network of tubules increases the surface area for the storage of key enzymes and the products of these enzymes

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7
Q

What is the nucleolus?

A

A dense body within the nucleus where ribosomes are made. It contains DNA, rRNA and ribosomal proteins.

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8
Q

What is the golgi apparatus/ vesicles?

A

The golgi apparatus is several stacks of flattened, membrane-bound sacs (the amount depends on how much they need to transport) formed by the fusion of vesicles from the endoplasmic reticulum.
It is responsible for modifying proteins and packages them in vesicles for transport.
Then, it classifies and modifies these vesicles and distributes them into the places where they are used in the cell.

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9
Q

What are ribosomes?

A

Made of ribosomal RNA and protein, found free in the cytoplasm or attached to endoplasmic reticulum.
They are the site of protein synthesis.
Composed of two subunits, a smaller and a larger subunit. Larger subunit contains two RNA binding sites. The mRNA attaches to the smaller subunit.

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10
Q

What is the rough endoplasmic reticulum (RER)?

A

A system of interconnected membrane-bound, flattened sacs
Ribosomes are attached to the outer surface
Proteins made on these ribosomes are transported through the ER (endoplasmic reticulum) to other parts of the cell
They play a central role in the synthesis of proteins

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11
Q

What is the function of mitochondria?

A

the mitochondria are the site of the later stages of aerobic respiration
The function of mitochondria is to synthesise ATP

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12
Q

What are lysosomes?

A

Lysosomes are spherical sacs containing digestive enzymes.
They are bound by a single membrane.
They contain the enzymes that help break down unneeded structures in the cell.
And they contain the enzymes that help break down the whole cell when old cells are being replaced or during development.
The acrosome is a special form of the lysosomes.

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13
Q

What are prokaryotic cells?

A

Prokaryotic cell means ‘before the nucleus’.
Prokaryotic cells do not have nuclei or other membrane bound cell organelles.
Prokaryotes are extremely small with diameters between 0.5 and 5 um.
Their DNA is not associated with any proteins and lies free in the cytoplasm
A cell wall is always present
Prokaryotes contain 2 groups called bacteria and archaea

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14
Q

What are eukaryotic cells?

A

Eukaryotic means ‘true nucleus’
They are larger than prokaryotic cells with diameters 20um or more
They do not all have a cell wall
They contain discrete membrane bound organelles such as nuclei and mitochondria

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15
Q

What are gametes?

A

sex cell (e.g. sperm and egg, pollen and ovum)

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16
Q

Name organisms which have eukaryotic cells

A

Animals, plants, fungi, protists

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17
Q

What is the process of protein traffiking?

A
  1. Transcription of DNA to mRNA
  2. mRNA leaves the nucleus
  3. Protein made on ribosomes enter rough ER
  4. Protein moved through the ER assuming 3D shape on route
  5. Vesicles pinched off the rough ER contain the protein
  6. Vesicle from rough ER fuse to form the flattened sacs of the golgi apparatus
  7. Proteins are modified within the golgi apparatus
  8. Vesicles pinched off the golgi apparatus contain the modified protein
  9. Vesicle fuses with cell surface membrane releasing protein, such as extracellular enzymes
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18
Q

Describe how a protein is modified, packaged and secreted

A

Proteins are packaged and transported in vesicles by the rER. Vesicles fuse to form the golgi apparatus. Proteins are modified within the golgi apparatus. The vesicles pinched off the golgi apparatus contain the modified protein The vesicles then fuse with cell surface membrane releasing proteins by exocytosis.

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19
Q

What happens during fertilisation?

A

The nucleus of the sperm fuses with the nucleus of the egg to produce a zygote (fertilised egg). This contains the full number of chromosomes eg. diploid

20
Q

What is the acrosome?

A

Contains digestive enzymes in the sperm head

21
Q

What happens in an acrosome reaction?

A

When a sperm reaches the egg cell, it binds to its outer layer (the zona pellucida) through attachment to sperm binding proteins. The acrosome swells and fuses with the sperm cell surface membrane
Digestive enzymes that are contained in the acrosome are released
These enzymes digest a tunnel through follicle and then the zona pellucida so that the sperm can reach the plasma membrane of the egg cell
The plasma membranes of the sperm cell and the egg cell fuse and the sperm releases its nucleus into the egg cytoplas

22
Q

Describe the role of the acrosome in fertilisation:

A

The acrosome of the sperm cell fuses with the sperm cell surface membrane and releases digestive enzymes which break down the zona pellucida.

23
Q

Explain why a defective acrosome reaction may result in male infertility

A

The egg cell is protected by the zona pellucida, if the acrosomes are defective the digestive enzyme won’t be released which means the zona pellucida will not break down and sperm will not be able to fuse with the egg.

24
Q

What is an egg cell?

A

Cytoplasm contains nutrients for growth of the developing embryo.
There is an outer layer called the zona pellucida - this changes after fertilisation so that no further sperm can penetrate.
Follicle cells outside the zona pellucida form a protective coating around the egg cell.

25
Q

What adaptions of the egg cell are there?

A

large cell with lots of cytoplasm- means cells are ready to divide immediately after fertilisation
zona pellucida - releases chemicals to attract sperm
cortical granules - contains enzymes to harden the zona pellucida to prevent polyspermy
lipid droplets - provide energy store for cell divisions

26
Q

What are the sperm cells adaptions?

A

Streamlined shape for faster swimming.
Tail (flagellum) enables the sperm to swim.
Contain lots of mitochondria to provide ATP for movement.
The head of the sperm contains the acrosome (a type of lysosome) - this is filled with digestive enzymes which break down the egg’s zona pellucida and allow the sperm to reach the egg cell membrane.

27
Q

What is meant by a homologous pair of chromosomes?

A

Identical pair of chromosomes carrying the same genes at the same loci

28
Q

What is the process of a cortical reaction?

A

The fusion of the sperm cell and egg cell stimulates the cortical granules to move and fuse with the egg cell surface membrane
Cortical granules (secrete) release their contents (by exocytosis) into the zona pellucida
These contents react with the zona pellucida causing it to thicken/harden which prevents other sperm cells from entering
The sperm and egg cell nuclei then fuse

29
Q

Describe the events of fertilisation that occur after the acrosome reaction.

A

Sperm fuses with the egg cell surface membrane
Cortical granules release their contents into the zona pellucida
This causes the zona pellucida to thicken/harden preventing other sperm from entering

30
Q

What is meiosis?

A

Cell division that results in a halving of the chromosome number and a reshuffling of alleles
Produces gametes (sex cells)
Meiosis consists of 2 divisions called meiosis I and Meiosis II
It results in the production of four haploid nuclei and creates genetic variation among offspring

31
Q

What happens in meiosis 1?

A

a reduction division, resulting in the production of 2 daughter nuclei with half the number of chromosomes of the parent nucleus

32
Q

What happens in meiosis 2?

A

second division, chromatids separate and haploid gametes form

33
Q

What is crossing over?

A

Occurs during meiosis I
Homologous chromosomes come together as pairs and all 4 chromatids come into contact
At these contact points, chromatids break and rejoin exchanging sections of DNA between non-sister chromatids
The point where the chromatids break is called a Chiasma (chiasmata)
Many chiasmata may form anywhere along the length of the chromosome leading to chromosomes containing new combinations of alleles from both parents. This results in genetic variation
Crossing over does NOT occur between the sex chromosomes

34
Q

What is independent assortment?

A

In meiosis I
Each gamete ends up with only one of the homologous pairs of chromosomes
The independent assortment of chromosomes as they line up during meiosis is random and either chromosome from each pair could be in either gamete
This means gametes can end up with many different combinations of maternal or paternal chromosomes

35
Q

Explain how meiosis gives rise to genetic variation in gametes.

A

Meiosis gives rise to genetic variation because of independent assortment and crossing over. Independent assortment means gametes can end up with many different combinations of maternal or paternal chromosomes. Crossing over involves swapping of sections of chromosomes.

36
Q

What is linkage?

A

2 genes with a locus on the same chromosome are linked together and will tend to be passed on as a pair of genes

37
Q

What are autosomes?

A

all chromosomes except sex chromosomes

38
Q

What is the locus?

A

the position of a gene on a chromosome

39
Q

What is sex linkage?

A

Genes whose loci are on the X or Y chromosomes (sex chromosomes) have different inheritance patterns from genes on all the other chromosomes (autosomes).
Women are XX, while men have are XY
These genes are said to be sex-linked, because their inheritance is affected by whether a person is male or female.

40
Q

If a sex-linked gene has a recessive allele for a particular condition, will it be more common in men or women?

A

men

41
Q

Why is X linkage more common?

A

the X chromosome is larger
part of it does not have a homologous section on the Y chromosome, therefore only one allele of a gene will be present and so will always be expressed.

42
Q

What do homologous regions carry?

A

Do NOT carry sex-determining genes

43
Q

What do non-homologous regions carry?

A

sex-determining genes and other genes

44
Q

What are some examples of X-linked genes?

A

haemophillia, red-green colour blindness and duchenne muscular dystrophy

45
Q

What does TREV Goes Mad Singing For Everyone stand for?

A

Transcription
mRNA to DNA
proteins made on RER
Vesicles
Golgi apparatus
Modified and packaged
Secretary vesicles
Fusion of cell membrane
Exocytosis

A-level Biology (48 decks)

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