Topic 3 - Voice of the Genome

Question 1

Describe the structure and function of the nucleus.

Answer 1

Structure - Surrounded by a double membrane, has pores that allows molecules (such as mRNA) to enter and leave.
Function - Stores DNA, coordinates cell activities.

Question 2

Describe the structure and function of the nucleolus.

Answer 2

Structure - Found within the nucleus, made of proteins and RNA.
Function - Produces ribosomes.

Question 3

Describe the structure and function of the rough endoplasmic reticulum.

Answer 3

Structure - A series of flattened sacs, with large numbers of ribosomes at the surface.
Function - Protein synthesis and folding of proteins.

Question 4

Describe the structure and function of the smooth endoplasmic reticulum.

Answer 4

Structure - A series of membrane-bound sacs, without ribosomes at the surface.
Function - Produces and processes lipids.

Question 5

Describe the structure and function of the golgi apparatus.

Answer 5

Structure - flat, curved, fluid-filled sacs surrounded by vesicles.
Function - Processes and packages proteins and lipids, produces lysosomes.

Question 6

Describe the structure and function of the mitochondria.

Answer 6

Structure - bound by a double outer membrane, inner membrane folded to increase surface area.
Function - site of respiration and ATP production.

Question 7

Describe the structure and function of centrioles.

Answer 7

Structure - hollow cylinders containing microtubules.
Function - involved in cell division.

Question 8

Describe the structure and function of ribosomes.

Answer 8

Structure - composed of two subunits, either membrane-bound or free in the cytoplasm.
Function - site of protein synthesis (translation)

Question 9

Describe the structure and function of lysosomes.

Answer 9

Structure - vesicles filled with digestive enzymes bound by a membrane.
Function - breakdown of any cell’s waste, destroy disease-causing organisms that enter the cell.

Question 10

Outline the role of the RER and golgi apparatus in transporting proteins.

Answer 10

-Proteins are produced on the ribosomes in the RER, and are then packaged and processed.
-Transported in vesicles to the golgi body.
-Modified and repackaged to be transported around the cell, or to leave the cell in the case of extracellular enzymes.

Question 11

Describe the structure and function of the prokaryotic cell wall.

Answer 11

Structure - forms a rigid outer covering over the cell, made of peptidoglycan.
Function - provides strength, support and protection against damage.

Question 12

Describe the structure and function of the capsule.

Answer 12

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

Question 13

Describe the structure and function of a plasmid.

Answer 13

Structure - circular molecules of DNA
Function - DNA replication, transferring DNA between bacteria, gene expression.

Question 14

Describe the structur and function of the flagellum.

Answer 14

Structure - a long, thin projection attached to the cell wall.
Function - movement; propels the cell forwards using a corkscrew motion.

Question 15

Describe the structure and function of the pili.

Answer 15

Structure - hair-like extensions on the surface of bacterial cells.
Function - help cells adhere to various surfaces, primarily each other.

Question 16

Describe the structure and function of mesosomes.

Answer 16

Structure - infolds of the plasma membrane, associated with enzymes.
Function - site of respiration

Question 17

How are mammalian eggs adapted for function?

Answer 17

-Zona pellucida to prevent polyspermy.
-Haploid nucleus to restore a full set of chromosomes at fertilisation.

Question 18

How are mammalian sperm adapted for function?

Answer 18

-Contain many mitochondria for energy required for moving.
-Acrosome contains digestive enzymes which break down the zona pellucida of the egg.

Question 19

Describe the process of mammalian fertilisation.

Answer 19

-Acrosome reaction - enzymes in the acrosome digest the zona pellucida. Sperm nucleus enters the egg cell.
-Cortical reaction - causes zona pellucida to harden, preventing polyspermy.
-Nucleic fusion - restoring full set of chromosomes, forming a diploid zygote.

Question 20

What is a locus?

Answer 20

The fixed position of a gene on a chromosome.

Question 21

What is meant by autosomal linkage?

Answer 21

Where two or more genes are located on the same (non-sex) chromosome, so are inherited almost as if they were the same gene. The closer the loci, the closer the linkage, as the genes are less likely to be recombined.

Question 22

What is meant by sex-linkage?

Answer 22

Where an allele is located on one of the sex chromosomes, meaning its expression depends on the sex of the individual.

Question 23

What is meant by polygenic inheritance?

Answer 23

Where a characteristic is determined by several different genes at different loci.

Question 24

Describe the two types of phenotypic variation.

Answer 24

-Continous - variation exists as gradual changes over a range (no set groups), such as height
-Discontinuous - variation exists as distinct categories (within set groups), such as blood group.

Question 25

Suggest factors that cause a phenotype to show continuous variation.

Answer 25

-If the characteristic is determined by more than one gene. -If the environment has an effect on the phenotype.

Question 26

In which ways does meiosis ensure genetic variation?

Answer 26

It produces non-idential gametes through: -Crossing over of alleles between chromatids -Independent assortment of chromosomes.

Question 27

Explain the role of mitosis.

Answer 27

Produces genetically identical daughter cells. Useful for growth, repair, and (in prokaryotic cells) asexual reproduction.

Question 28

What is a stem cell?

Answer 28

Undifferentiated cells, that can divide indefinitely and turn into other specific cell types.

Question 29

What is meant by pluripotent and totipotent stem cells?

Answer 29

-Totipotent - can develop into any cell type including the placenta and embryonic cells. -Pluripotent - an develop into any cell type excluding the placenta and embryonic cells.

Question 30

State some uses of stem cells.

Answer 30

-Treat diseases,, such as Parkinsons and multiple sclerosis. -Replace damaged tissues, such as spinal chords.

Question 31

Why is the use of stem cells controversial?

Answer 31

-Involves killing embryos -There is a risk of infection after transplant. -However; could save lives and greatly improve quality of life.

Question 32

How do cells become specialised?

Answer 32

-Environmental stimuli cause some genes become switched on or off. -The active genes are transcribed and translated into proteins, which are then used for the specific function of the cell.

Question 33

Define phenotype.

Answer 33

The expression of an organism's genes, combined with its interaction with the environment.

Question 34

What is meant by epigenetics?

Answer 34

A heritable change in gene function without change to the base sequence of DNA.

Question 35

How does DNA methylation affect gene transcription?

Answer 35

Involves the addition of a CH₃ group to one of the bases. Prevents transcription factors from binding. Therefore, gene transcription is supressed.

Question 36

How can histone modification affect gene expression?

Answer 36

-Addition of an acetyl group activates chromatin, allowing transcription. -Addition of a methyl group can either activate or inactivate chromatin depending on the position.

Question 37

How are epigenetic changes passed on?

Answer 37

Because the changes affect cell division, all cells that arise from the altered cells will possess the modifications. This includes gametes, meaning the changes are hertiable.