3C

Question 1

what are stem cells

Answer 1

• a cell that can divide by mitosis, each new cell has the potential to to remain stem cell or become speicialised cell, there are three main types of stem cells:
• Totipotent
• Pluripotent
  -multipotent

Question 2

what are totipotent cells

Answer 2

• can divide and produce any type of cell
• morula is a solid ball which is like a zygote and embryoic cells
• cells will lose their ability to deffrentiate into any cell type

Question 3

what are Pluripotent cells

Answer 3

• morula will divide further and form blastocyst which has an outer layer of cells and an inner mass of cell, the outer layer forms placenta and inner layer will no longer become totipotent
• pluripotent embryonic stem cells can deffrintiate to any cell present in embryo but not placenta and umbilical chord

Question 4

what are multipotent cells

Answer 4

• they are found in adult tissues but can only be specialise to certain type of cells

Question 5

how are stem cells used in medicine

Answer 5

• stem cells can be used to replace damaged cells, example:
  in bone marrow cancer stem cells can be transplanted in the bone marrow to replicate new cells

Question 6

how are embryonic cells used in medicine

Answer 6

• stem cells can be used therapeutic treatment of many diseases, but the wasted embryo from IVF is used, it can develop into a human being this is one of ethical issues

Question 7

how are adult cells used in medicine

Answer 7

• they are present in brain and bone marrow to produce essential tissues and repair damaged cells
• less controversial because the donor will be able to give permission but blood type must match and body antigens

Question 8

how are stem cells specialised through differential gene expression

Answer 8

• only certain genes in the DNA are activated and get expressed
• some genes are activated, mRNA is transcribed from active gene, the mRNA is translated to form proteins, these proteins modify the cell to become sepcialised

Question 9

what are transcription factors and what is their function

Answer 9

• is a protein that controls the transcription of genes by binding to a specific region of DNA
• activators are transcription factors that increase the rate of transcription, repressors are same but they decrease the rate of transcription

Question 10

how do transcription factors decrease or increase the rate of transcription

Answer 10

• by binding to the promoter region, by either assisting RNA polymerase to bind or to prevent it from binding

Question 11

how are gene expression controlled through operons

Answer 11

• an operon is a section of DNA that has structural genes transcribed together, promotor region (where RNA polymerase binds to) and operator (where transcription factors bind to),activators and repressors

Question 12

what are lac operon

Answer 12

• they are controlled by the same operator, controls the production of enzyme lactase which breaks down lactose, its only synthesized when lactose is present

Question 13

what is the structure of lac operon

Answer 13

• promoter and operator
• lac Z(codes for lactase), lac A and lac Y

Question 14

what do post-transcriptional modification mechanisms include

Answer 14

• splicing
• alternative splicing

Question 15

what does happen during splicing

Answer 15

• when protein are synthesized, they contain non-coding sections, they are called introns, whilst sections of coding DNA are called exons, splicing occurs which remove introns and join the exons together, then the new protein is trancribed to produce pre-mRNA

Question 16

what is alternative splicing

Answer 16

• a particular exon may or may not be incorporated into the pre-mRNA to produce different pre-mRNA molecules, a single eukaryotic gene may code for many proteins

Question 17

how phenotype is the result of an interaction between genotype and the environment

Answer 17

• when genetic variation is present within species which will cause phenotypic variation
• environments can affect the phenotype by affecting the conditions that will help the organism to grow, it might effect their diet when specific food is not present or plants are not exposed to enough sunlight

Question 18

how does epigenetic modification alert the activation of certain genes

Answer 18

• epigenetics involve switching on and off, in order to survive enviromental conditions. in eukaryotic cells nuclear DNA is wrapped around proteins called histones to form chromatin, it can be modified in different ways to alter gene expression including:
• methylation of DNA
• histone modification via acetylation of amino acid tails

Question 19

what is an epigenome

Answer 19

• modification are called epigenetic tags and all of tags in an organism are called epigenome

Question 20

how does DNA methylation occur and what does it do

Answer 20

• methyl group can be added to DNA to change the activity of a gene
• methylation of DNA suppresses the transcription of the affected gene by inhibiting the binding of transcription factors and other enzymes

Question 21

how does Acetylation of histones occur and what does it do

Answer 21

• Acetyl groups can be added to lysine amino acids on histone proteins which is positively charged adding acetyl group will remove the positive ions which will cause the DNA to be less tight

Question 22

how epigenetic modifications can be passed on following cell division

Answer 22

• the epigenome is heritable which means that when a cell divides and replicates epegentic changes can be passed on the daughter cells, which can cause beneficial changes to the species

Question 23

how are phenotypes affected by phenotypes

Answer 23

• characteristics that are controlled by single gene are known as monogenic, these show discontinuous variation
• characteristics that are controlled by several gene are known as polygenic, these show continuous variation