Topic 3

Question 1

Structure and function of different parts of a prokaryotic cell (bacteria/archea)

Answer 1

—>Ribosomes- site of protein synthesis
—>Nucleoid- for prokaryotes they have a single circular length of DNA carrying essential information, DNA is folded into nucleoid.
—>Cell surface membrane- controlling what goes in/out
—>Cell wall- made of peptidoglycan (polymer of sugar and amino acids)
—>Memosomes- Infolding of the inner membrane
—>Flagellum- rotates for movement
—>Pili- thin protein tubes allowing bacteria to stick to surfaces
—>Plasmids- double stranded DNA in a circular structure ( provide toxin producing genes)
—>Capsule- used for production and prevent dehydration

Question 2

Structure and function of parts in Eukaryotes (fungi/animal cells)

Answer 2

—>rER- series of single/flattened sacs, folds and processes proteins on ribosomes.
—>sER- system of membrane bound sacs, sER produces/processes lipids.
—>Nucleus- surrounded by a double membrane (envelope) contains pores allowing molecules to enter/leave cell. Nucleus contains DNA wrapped around histone proteins in complex called chromatin and a nucleous that produces ribosomes.
—>Centrioles- two hollow cylinders (right angles) creating the spindle for cell divisions
—>Lysosome- enclosed by single membrane, contains digestive enzymes that destroy old organelles and pathogens.
—>Golgi apparatus- single curved sacs enclosed by membrane formed by vesicle fusion from ER. It modifies proteins and packs them in vesicles for transport.
—>ribosomes- protein synthesis
—>mitchrocondria- surrounded by double membrane (envelope). Inner membrane folds into cristae and central area contains jelly called matrix. Mitchrocondria contains DNA and ribosomes it’s also site of respiration.

Question 3

Steps of Production of proteins and route through cell

Answer 3

1)Transcription of DNA to mRNA, mRNA leaves nucleus
2)Protein on ribosomes enter rER and protein gains 3D shape
3)vesicles fuse to form flattened sacs of Golgi apparatus, here protein is modified and prepared for transport (packed in vesicles)
4)Vesicles pinched and fuse with membrane releasing proteins (exocytosis)

Question 4

Structure and function of different parts of sperm cell

Answer 4

—>Flagellum- used for movement
—>Haploid nucleus- contains half number of chromosomes (so full amount restored after fertilisation)
—>Acrosome- contains enzymes that digest outer layer of egg
—>Middle region (mitchrocondria) - provide energy (respiration) for movement

Question 5

Egg cell structure and function

Answer 5

—>lipid droplets- provide energy
—>Folicile cells from ovary- act as protection and hardern after sperm enters
—>Cytoplasm-full of energy
—>membrane
—>Zona pellucida- jell like layer stopping more than one egg fertilising
—>haploid nucleus- half chromosomes
—>Vesilcles (cortical granules)- release substance to harden zona pellucida

Question 6

Fertilisation steps

Answer 6

1)Sperm reaches ovum so chemicals released triggering acrosome reaction (enzymes digest zone pellucida)
2)sperm fuses with egg membrane and sperm nucleus enters egg
3)cortical reaction occurs hardening zona pellucida
4)full set of chromosomes restored forming diploid zygote

Question 7

What is a gamete

Answer 7

Contains half the number of chromosomes one from each homologous pair.

Question 8

What is mitosis

Answer 8

Mitosis produces new body cells as organism grows and develops, it retains full number of chromosomes (diploid)

Question 9

What is meosis

Answer 9

Produces gametes with haploid. Occurs in ovaries/testies in animals but ovaries/anthers in plants. Meosis creates genetic variance in offspring.

Question 10

What is crossing over

Answer 10

1) homologous chromosome pair is replicated forming chromatids (the point at which the chromatids break is called chiasma)
2) The chromatids separate and gametes are formed (each with half the amount of chromosomes)

Question 11

How is genetic variation achieved through meosis

Answer 11

–>Crossing over- exchange of DNA sections between homologous chromosomes
–>Independent assortment- there are various ways paternal/maternal chromosomes can be distributed between daughter cells

Question 12

Describe what Mendel did with garden pea plants

Answer 12

Mendel analysed patterns of inheritance in garden peas. He crossed homozygous (pure breeding) tall purple plants with short white plants.
-He found that all offspring (f1 generation) were tall purple
-But crossing further he found (F2 generation) there was a mix of different plants.

Question 13

What did Mendel conclude from his peas experiment

Answer 13

Inheritance of one pair of factors is independent of inheritance of other pairs. However this is only the case if genes are on different chromosomes and independently assorted

Question 14

What does sex linked mean

Answer 14

Sex linked- genes with loci on the same sex chromosomes (X/Y chromosomes)

Question 15

What is the cell cycle

Answer 15

Process in which cells divide to produce two genetically identical daughter cells for growth/repair/asexual reproduction

Question 16

What are the three stages in the cell cycle

Answer 16

-Mitosis (Prophase,metaphase,anaphase,telophase)
-Cytokinesis (cytoplasm divides to form 2 new cells)
-Interphase (Cell grows, new organelles grown,finally chromosomes replicated)

Question 17

Stages of mitosis explained

Answer 17

1)Prophase- chromosomes become visible and nucleus breaks down and disappears, spindle formed. Then centrioles move to either end of cell.
2)Metaphase-chromosomes with 2 sister chromatids line up and attach to spindle fibres which are attached to centrioles.
3)Anaphase-spindle fibres contract pulling chromatids apart
4)Telophase-chromosomes decondence and membrane of nucleus reform

Question 18

Stages in interphase

Answer 18

1)G1 (gap 1 phase)- cell grows, DNA replicates and protein synthesis occurs.
2)S phase- chromosomes are replicated and begin to condense to form chromatin
3)G2 (gap 2)- Cell prepares to divide and replicates organelles for a full set in each new cell

Question 19

How does mitosis ensure genetic consistency

Answer 19

As each daughter cell contains same number and type of chromosomes as parent cell.
This is achieved as DNA replicates prior to nuclear Division and the arrangement of chromosomes on spindle/chroatid separation on poles

Question 20

What is a multipotent stem cell

Answer 20

Give rise to variety of different cell types

Question 21

Pluripotent stem cell

Answer 21

Give rise to variety of cells other than placental cells

Question 22

Totipotent stem cells

Answer 22

Give rise to all types of specialised cells, a cell is totipotent when an embryo consists of 8 identical cells

Question 23

Ethical issues for using stem cells in medication

Answer 23

-is it acceptable to use human embryos that are created for research
-when does an embryo become a human with rights

Question 24

What happens during therapeutic cloning (making organs from own cells)

Answer 24

1)diploid cell removed
2)cells nucleus fused with ovum, from which haploid nucleus has been removed and diploid cell results
3)this process is somatic cell nuclear transfer. The stem cells created can be used.

Question 25

How did the creation of Dolly support therapeutic cloning

Answer 25

1)Mammary cells grown in culture, nucleus removed from donor egg cell
2)Cells fused and grown in culture
3)this form embryo that in implanted in another sheep
4)embryo develops and lamb (dolly) that has identical chromosomes to mammary donor

Question 26

What is the Role of active mRNA

Answer 26

mRNA is translated into proteins in cell, these proteins control processes (i.e enzymes) also proteins can control part of cell structure.

Question 27

What does loci mean

Answer 27

Location of genes on a chromosomes

Question 28

What is the epigenome (switching genes on/off)

Answer 28

Epigenome Influences which genes can be transcribed into a cell

Question 29

What is DNA methylation

Answer 29

Attaching methyl group to cystosine as epegenic marker. This stops transcription of mRNA by preventing binding of RNA polymerase.

Question 30

Lac operon

Answer 30

When Lacoste is present- lactose binds to repressor preventing binding to DNA and B glactosidase gene expressed. mRNA coding for B glactosidase transcribed and protein produced.

When lactose is not present- repressor molecule binds to DNA preventing transcribed of B glactosidase, RNA polymerase can’t bind to DNA promoter region and protein not produced.

Question 31

Specialisation (steps for stem cells)

Answer 31

1)Stimulus acts on unspecialised cell
2)activator/repressor molecule bind to promoter region, some genes switch on some off
3)active genes are transcribed forming RNA
4)then mRNA translated into protein (on ribosome)
5)protein produced has ability to change structure/function of cell.

Question 32

What is a phenotype

Answer 32

Characteristic of an organism due to interaction of genes with environment

Question 33

What is continuous and discontinuous variation

Answer 33

CV-variation in a range (mass/height)
DC-only take particular values (gender/size)

Question 34

What is monogenic and polygenic inheritance

Answer 34

Monogenic-characteristics only influenced by one gene ( characteristics show discontinuous variation)
Polygenic-several genes at different loci involved in determining characteristics (continuous variation)