EQ - Topic 3: Voice of the Genome

Give two functions of the golgi apparatus (2)

• modifies proteins

• forms vesicles

Compare and contrast the structures of the golgi apparatus and the rER

• both are membrane bound organelles

• both consist of folded membrane bound sacs

• both fluid-filled sacs

• rER has ribosomes attached to it’s surface whereas golgi apparatus does not

• golgi apparatus has vesicles at the end whilst rER does not

bacteria do not posses golgi apparatus

hence the polypeptide chain cannot be modified properly

therefore the protein is incorrectly folded

Describe the function of the plasmodesmata (2)

• cytoplasmic connection between cells

• which allows transport between cells

DNA synthesis in bacterial cell cultures has been investigated.

Describe how DNA is organised in a bacterial cell (3)

in prokaryotics there are:

• large circular DNA

• several small plasmids

• DNA is found in the cytoplasm and not in the nucleus

• vesicles fuse with golgi apparatus

• proteins are modified inside golgi apparatus

• protein packaged into secretory vesicles

• vesicles fuse with cell surface membrane

• lysosomes fuse with cell surface membrane

• lysosomes release it’s contents

• by exocytosis

Explain why the nucleus cannot be observed at the end of prophase (2)

the nuclear envelope breaks down into small vesicles

• because DNA is coiled into individual chromsomes (they condense)

Explain the role of meiosis in the production of gametes (3)

produces haploid cells

genetic variation occurs through crossing over

crossing over involves the swapping of sections of chromatids

Explain the role of meiosis in the production of genetically variable sperm cells (5)

• meiosis produces 4 haploid cells

• genetic variation occurs due to crossing over

• whereby the homologous chromosomes join at the chiasmata where tey exchange sections of chromatids

• this reults in exchange of alleles between chromatids

• and thus the formation of recombinants

• genetic variation also occurs due to independent assortment

• where homologous chromsoes line up in different combinations

• resulting in new combination of alleles in the gametes

crossing over:

• the homologous chromosomes join at the chiasmata and swap genetic information as the chromatids are produced with different combinations of alleles

• and leads to the formation of recombinant chromatids

• e.g Ab/ aB

independent assortment:

• different combinations of chromosomes (1 and 2) are prodcued

• therefore the alleles for A and B could be in the same gamete as C or c

Give two differences other than size between the structure of a sperm cell and a structure of a female gamete (2)

• sperm has a flagellum but female gamete does not

• sperm has acrosomes in it’s head but female gamete does not

• no cortical granules in sperm but are present in the ovum

Explain how the structure of an egg cell is related to it’s function as a gamete (4)

• haploid nucleus

• the haploid state allows for the restoration of diploid number at fertilisation

• corical granules

• secrete it’s contents which cause the zona pellucida to thicken and harden preventing any other sperm cells from enetering the egg cell

Describe the process of fertilisation in mammals (4)

• sperm uses flagella for movement to swim to the ovum

• whereby mitochondria in the mid-piece release energy through repsiration for movement

• the acrosomes in the head release digestive enzymes which break down the zona pellucida —→ the acrosome reaction

• the egg cell membrane fuses with the sperm cell membrane

• the cortical granules release its contents which cause the zona pellucida to thicken and harden so no sperm cells can penetrate the cell —→ cortical reaction

• fusion of sperm and egg nuclei (which are both haploid) to restore the number of chromosomes

Describe the role of the acrosome in fertilisation (3)

the acromosome fuses with the cell surface membrane of the sperm cell

• digestive enzymes are released

• which break down the zona pellucida hence can penetrate through the egg cell membrane

Describe how the acrosome is involved in the digestion of the zona pellucida

the membrane of the acrosome fuses with the plasma membrane of the sperm cell

releasing enzymes from the acrosome

by exocytosis