Topic 3 - Voice of the Genome

Question 1

Describe the structure of the nucleus.

Answer 1

Surrounded by a double membrane porous envelope, containing DNA wrapped around histone proteins in a chromatin complex, and a nucleolus.

Question 2

What is the role of the nucleolus?

Answer 2

The site of ribosome production.

Question 3

Describe the structure and function of the rough endoplasmic reticulum (rER).

Answer 3

A series of flattened sacs enclosed by a membrane with ribosomes on the surface, the rER folds and processes proteins into 3D shape.

Question 4

Describe the structure and function of the smooth endoplasmic reticulum.

Answer 4

A system of membrane bound sacs with no ribosomes on the surface, it produces and processes lipids.

Question 5

Describe the structure and function of the Golgi apparatus.

Answer 5

A series of fluid-filled curved sacs with vesicles on the edges. It modifies (adds saccharide chains) and packages proteins after receiving them from the rER into vesicles, and lipids, also producing lysosomes

Question 6

Describe the structure and function of the mitochondria.

Answer 6

Site of aerobic respiration. Double membrane organelle, inner membrane is folded forming projections called cristae, fluid matrix inside contains enzymes for cellular respiration.

Question 7

Describe the structure and function of centrioles.

Answer 7

Hollow cylinders with a ring of microtubules, separates chromosomes during mitosis.

Question 8

Describe the structure and function of ribosomes.

Answer 8

Site of protein synthesis, composed of large and small subunit, 80S in eukaryotes, 70S in prokaryotes.

Question 9

Describe the structure and function of lysosomes.

Answer 9

Single membrane vesicles containing digestive enzymes. to digest invading cells or break down old cell components.

Question 10

Describe the protein production and transport process.

Answer 10

1) Proteins are produced in the ribosomes.
2) Proteins from rER ribosomes are folded and processed (i.e. saccharide chains added) in the rER
3) Proteins are transferred to Golgi apparatus in vesicles
4) They are modified (i.e. carbohydrate added to form glycoprotein)
5) Proteins are packaged into vesicles to be transported around the cell or are secreted via exocytosis from the cell

Question 11

Name organelles and their functions that are unique to prokaryotes/bacteria cells.

Answer 11

Slime capsule - Layer of slime to retain moisture and protects from immune system cell attacks
Cell wall - Provides strength & support, made of peptoglycan
Plasmid - Circular loops of DNA
Flagellum - Tail structure for movement
Pilli - Hair-like structures, allow exchange of genetic material between cells
Mesosome - Inward folds of plasma membrane, unknown function (artifacts of microscopy or needed for respiration?)

Question 12

What is a haploid and diploid cell?

Answer 12

Diploid cells contain 23 pairs of chromosomes (=46), so normal body cells.
Haploid cells contain 23 single chromosomes, so are gamete or sex cells (sperm and ova)

Question 13

What are the two reactions involved in fertilization?

Answer 13

The acrosome reaction and the cortical reaction

Question 14

Describe the acrosome reaction.

Answer 14

1) When a sperm cell makes contact with the zona pellucida of the egg cell
2) Digestive enzymes are released from the acrosome of the sperm
3) These digest the zona pellucida

Question 15

Describe the cortical reaction.

Answer 15

1) The sperm head fuses with the cell membrane of the egg cell, allowing sperm nucleus to enter the cell
2) Contents of vesicles called cortical granules are released
3) These chemicals make zona pellucida thicken, preventing polyspermy (making it impenetrable to other sperm)
4) Nuclei fuse, a diploid zygote is formed, thus it is fertilized.

Question 16

What is the zona pellucida?

Answer 16

A protective glycoprotein layer between the egg cell membrane and follicle cell coating that sperm must penetrate.

Question 17

What is the locus (pl. loci) of a gene?

Answer 17

The position of a gene on a chromosome

Question 18

What is a sex-linked characteristic?

Answer 18

When the locus of the allele that codes for a certain characteristic is on a sex chromosome (X or Y)

Question 19

Why are men more likely to inherit certain sex-linked disorders (i.e. red-green color blindness)?

Answer 19

The Y chromosome is smaller than the X so most sex-linked genes are only carried by X chromosome.
Since males have only one X chromosome, if men don’t have another copy of a certain allele, it is expressed even if it’s recessive, so are more likely than females to show recessive phenotypes for sex-linked genes.

Question 20

What is the function of mitosis?

Answer 20

For the growth, repair and asexual reproduction of cells.

Question 21

What are the 3 stages of the cell cycle?

Answer 21

Interphase, mitosis and cytokinesis

Question 22

What are the sub-stages of interphase?

Answer 22

G1: Cell growth, copies organelles
S: DNA replicates and condense to form chromatin
G2: Cell keeps growing, proteins needed for division are made

Question 23

What occurs during cytokinesis?

Answer 23

Cytoplasm divides, producing two identical daughter cells

Question 24

What are the stages of mitosis, what occurs during each stage?

Answer 24

1) Prophase: Chromosomes condense, centrioles form a network of spindle, nuclear envelope breaks down so chromosomes lie free in cytoplasm
2) Metaphase: Chromosomes line up along middle of cell, become attached to spindle by centromere
3) Anaphase: Centromeres divide, separating sister chromatids, spindles contract, pulling chromatids to opposite poles, chromatids look v-shaped
4) Telophase: Chromatids reach poles, uncoil to be long & thin again, they are chromosomes again. Nuclear envelope forms around each so there are 2 nuclei
- ->Cytokinesis

Question 25

Describe the steps of meiosis.

Answer 25

DNA replicates to form two copies of each chromosome
Chromosomes arrange into homologous pairs
First division - Homologous pairs are separated
Second division - pairs of chromatids are separated
4 new haploid daughter cells are formed, each with 23 chromosomes.

Question 26

What is the difference between mitosis and meiosis?

Answer 26

Mitosis produces 2 identical diploid daughter cells

Meiosis produces 4 identical haploid daughter cells as gametes

Question 27

What are 2 sources of genetic variation in meiosis?

Answer 27

Crossing over of chromatids and independent assortment of chromosomes

Question 28

How does crossing over of chromatids occur?

Answer 28

Before the first division of meiosis, chromatids of homologous pairs twist around each other, break off and rejoin the other, recombining genetic material –> same genes but different combination of alleles

Question 29

How does independent assortment of chromosomes occur?

Answer 29

When gametes are produced, different combinations of maternal and paternal chromosomes go into each cell, forming 4 genetically diverse haploid cells

Question 30

Why are genes with loci on the same chromosome linked?

Answer 30

Genes on the same chromosome will stay together during independent assortment, both alleles will be passed along together, unless crossing over splits them up. The closer the loci, the more closer they are linked

Question 31

What are stem cells?

Answer 31

Undifferentiated cells which have the potential to develop into any specialized cell.

Question 32

What are the 3 types of stem cells, how are they different?

Answer 32

Multipotent: can give rise to many types of cells
Pluripotent: can give rise to many types of specialized cells, but not extra embryonic cells
Totipotent: can give rise to all types of specialized cells

Question 33

What are the two sources of stem cells, what are some pros and cons?

Answer 33

Adult stem cells from bone marrow, can differentiate into a limited range of cells, less chance o rejection if patient’s own stem cells are used
Embryonic stem cells can differentiate into any body cell, but embryo must be destroyed in the process

Question 34

What diseases can stem cells treat?

Answer 34

Diabetes, Parkinson’s, nerve tissue/spinal cord injuries, heart disease

Question 35

What are some ethical objections to stem cell treatment?

Answer 35

Embryo killed in process, some argue a human individual is killed
Embryo cannot give permission to use its body tissue
Risk of infection when transplanted, risk of becoming cancerous cells

Question 36

What are modern solutions to ethical issues with stem cells, how is treatment regulated?

Answer 36

License and monitoring centers ensures trained staff carries out research
Codes of practice are put in place
Research proposals are checked so research isn’t unnecessarily repeated + resources aren’t wasted
Up to date info + advice given to governments and professionals

Question 37

Where are stem cells located in plants?

Answer 37

In meristem, or roots and shoots of plants (i.e. where it is growing)

Question 38

What is the process of cell specialization/differentiation?

Answer 38

1) A stimulus acts on unspecialized cells
2) Activator/repressor molecules can bind to promoter regions of DNA, causing some genes to be activated or repressed
3) Activated genes are transcribed to produce mRNA, which are translated on ribosomes to produce proteins
4) Proteins determine cell structure and function, cell is specialized

Question 39

Define phenotype.

Answer 39

The characteristic of an organism, resulting from the interaction of the genes and environment

Question 40

What’s the difference between continuous and discontinuous variation?

Answer 40

Continuous variation: Individuals in a population vary within a range, without distinct categories (e.g. height , mass)
Discontinuous variation: When individuals fall into distinct categories (e.g. blood group)

Question 41

What is are monogenic and polygenic characteristics?

Answer 41

Monogenic: A characteristic controlled by one gene
Polygenic: A characteristic controlled by multiple genes at different loci

Question 42

Give examples of the environment and genes affecting a phenotype.

Answer 42

Proto-oncogenes (regulate cell cycle) genetically predispose people to cancer, but smoking exposes them to chemicals which convert these into active oncogenes, causing uncontrolled cell division
Height is polygenic, but is affected by environment (nutrition)
Animal fur color: siamese cats have genes coding for fur-darkening tyrosinase, but is only activated below 31C, so extremities are dark

Question 43

What are epigenetic modifications?

Answer 43

Changes to DNA that don’t change the base sequence, affecting whether a gene is activated or repressed

Question 44

Explain methylation as an epigenetic modification.

Answer 44

Addition of methyl (-CH3) groups to DNA at CpG site (where cytosine and guanine are next to each other).
Methylation changes DNA structure, so proteins/enzymes can’t bind to gene, so gene is not expressed (is repressed/inactivated).

Question 45

What are histones?

Answer 45

Proteins that DNA wraps around to form chromatin

Question 46

Explain histone modification/acetylation as an epigenetic modification.

Answer 46

The addition of acetyl groups (COCH3) to histones, causing chromatin to be less condensed. Transcription proteins can bind to DNA, allowing genes to be transcribed, so gene is activated/expressed
The removal of acetyl groups causes chromatin to be highly condensed, DNA can’t be transcribed, so genes are repressed

Question 47

What are transcription factors?

Answer 47

Proteins that bind to DNA to activate/deactivate genes by increasing/decreasing the rate of transcription

Question 48

What are activators and repressors and what are their functions?

Answer 48

Activators increase the rate of transcription by helping RNA polymerase bind to DNA and begin transcription.
Repressors prevent RNA polymerase from binding, stopping transcription.

Question 49

What are operons?

Answer 49

In prokaryotes, transcription factors bind to operons, which are sections of DNA that contain structural genes (coding for useful proteins like enzymes), control elements (promoter and operator), and regulatory genes (code for activator and repressor)

Question 50

What is a promoter and operator?

Answer 50

Promoter is a DNA sequence located before structural genes that RNA polymerase binds to
Operator is a DNA sequence that transcription factors bind to.

Question 51

Explain the lac operon model in E. coli.

Answer 51

E. coli respires lactose if glucose is unavailable, genes for lactose-respiring enzymes are on the lac operon, which has 3 structural genes (lacZ, lacY, lacA) which produces proteins for lactose digestion.
When lactose is not present, the regulatory gene (lacI) produces the lac repressor, a transcription factor which binds to the operator site, blocking transcription as RNA polymerase can’t bind to the promoter.
When lactose is present, lactose binds to the repressor, changing its shape so it can’t bind to the operator site, so RNA polymerase can begin transcription of the structural lac genes.