y11 test3

Question 1

What are chromosomes?

Answer 1

Thread-like structures in the cell that contain DNA

Question 2

What is a gene?

Answer 2

A section of DNA that contains the instructions for a particular characteristic

Question 3

What is DNA?

Answer 3

found as chromosomes, its sequence determines how our bodies are made

Question 4

What is genetic code?

Answer 4

The sequence of bases within the DNA that ultimately code for proteins

Question 5

What are DNA bases?

Answer 5

Four chemicals found in DNA that make up the base sequence (A,T,C,G)

Question 6

What is a genome?

Answer 6

The entire genetic material of an organism

Question 7

What is the role of the DNA?

Answer 7

To code for proteins

Question 8

What were the aims of the human genome project?

Answer 8

-to search for genes linked to different diseases
-to better understand (and possibly treat) inherited disorder
-to create personalised medication
-to trace human migration patterns from prehistory

Question 9

What are some ethical concerns of the human genome project?

Answer 9

-could involve (embryonic) stem cells
-development of medicines could involve animal testing
-not everyone will be able to afford personalised medications

Question 10

What is the structure of DNA?

Answer 10

• DNA is in the shape of a double helix. It forms the genetic code and codes for proteins
• Each strand of DNA is made of a 5-carbon sugar phosphate backbone
• It is made of a series of repeated units called nucleotides, so DNA is a polymer

Question 11

What are nucleotides made of?

Answer 11

• phosphate, 5 carbon sugar and an organic base (A,T,G,C)
• A and T are complementary, held together in DNA by 2 hydrogen bonds
  G and C are complementary, held together in DNA by 3 hydrogen bonds

Question 12

Why does the DNA strand coil up into a double helix?

Answer 12

To protect the bases from pathogens

Question 13

What are the 2 stages in protein synthesis?

Answer 13

Transcription (DNA —> mRNA)
Translation (mRNA —> protein)

Question 14

What are the stages of transcription?

Answer 14

1) The DNA unzips and the gene that needs transcribing is exposed
2) RNA polymerase binds to the intron and starts ‘reading’ the DNA template strand
3) Complementary RNA nucleotides line up alongside the DNA template strand
4) A single stranded copy of the DNA is made
5) Once the mRNA is made, it is released from the DNA which reforms as a double helix. The introns are cut off
6) mRNA leaves the nucleus and moves to the ribosomes in the cytoplasm

Question 15

Why is only the gene needed exposed in transcription?

Answer 15

exposing all the genes isn’t energy efficient

Question 16

Is there a ‘C’ base in RNA nucletides?

Answer 16

No- the ‘T’ is replaced with a ‘U’

Question 17

Why does transcription take place?

Answer 17

The double stranded DNA is too large to leave the nucleus, so a smaller, single stranded mRNA is needed to fit through the nuclear membrane

Question 18

What is the exon?

Answer 18

the coding region, codes for a protein

Question 19

What is the intron?

Answer 19

the non-coding region, where the enzymes bind to ‘switch on’ the gene

Question 20

What are the stages of translation?

Answer 20

1) mRNA binds to the ribosomes
2) The ribosome reads the mRNA in groups of 3 bases- a triplet (codon)- 3 bases codes for 1 amino acid
3) Carrier molecules with the complementary base sequence to the mRNA triplet bind to the mRNA at the ribosome. Attached to the other end of the carrier molecule is an amino acid
4) The next 3 bases are read and another carrier molecule (tRNA) with a complementary base sequence brings in another amino acid. A peptide bond forms between the amino acids and the first carrier molecule leaves
5) A third amino acid is brought in by another carrier molecule which forms a peptide bond to the growing chain
6) When all the mRNA has been read, we are left with a sequence of amino acids called a polypeptide chain
7) This can then fold into a 3D shape, a protein which can then do its job as an enzyme, hormone, etc

Question 21

What is a mutation?

Answer 21

A change to the base sequence of the DNA

Question 22

What causes mutations?

Answer 22

can happen spontaneously
radiation
carcinogens
inbreeding

Question 23

How do mutations happen in the exon?

Answer 23

1) Silent mutations- sometimes if a base in the DNA is changed, it still codes for the same amino acid- e.g AGA –> AAG
2) Some mutations change the DNA base sequence- either a different amino acid is coded for, so we get a different protein. If this is an enzyme, it may mean that the shape of the active site is incorrect, so the enzyme won’t work

Question 24

Do all mutations have a serious effect?

Answer 24

No- mutations happen constantly and many don’t alter the structure/function of a protein

Question 25

What can mutations lead to in body cells or gametes?

Answer 25

In the body cells, mutations may lead to cancer. In gametes, mutations can lead to genetic mutations in the offspring

Question 26

How do mutations happen in the intron?

Answer 26

Could cause the gene to be switched on or off at the wrong time - this could mean a protein is made when it isn't needed, wasting energy or catalysing a reaction we don't need - this could mean we lack a protein we need

Question 27

What are alleles?

Answer 27

Different forms of a gene, can be dominant or recessive

Question 28

What does homozygous mean?

Answer 28

same copies of alleles- BB or bb

Question 29

What does heterozygous mean?

Answer 29

different copies of alleles- Bb or bB

Question 30

How do you draw a genetic diagram?

Answer 30

PARENTS: phenotypes- tall x dwarf genotypes- TT x tt gametes- T T x t t (IN CIRCLES) F1 GENERATION: phenotypes- tall x tall genotypes- Tt x Tt gametes- Tt x Tt (IN CIRCLES) F2 GENERATION: phenotypes- tall x tall x tall x dwarf genotypes- TT x Tt x Tt x tt ratio = 3:1 probability = 25% dwarf, 75% tall

Question 31

How do we draw a back cross?

Answer 31

We use it to determine if an organism is homozygous dominant or heterozygous Back crosses use a homozygous recessive individual as a parent

Question 32

Sickle cell anemia?

Answer 32

Caused by a recessive allele, causes sickle-shaped red blood cells SS = no disease Ss = carrier of disease ss = sickle shaped cells

Question 33

Cystic fibrosis?

Answer 33

Caused by a recessive allele, prevents movement of some substances across cells

Question 34

Polydactyl?

Answer 34

Caused by a dominant allele, babies are born with extra digits on their hands and feet

Question 35

What are the chromosomes for males and females?

Answer 35

Male - XY Female - XX

Question 36

If a disease recessive allele is on the Y chromosome, who can be affected?

Answer 36

Biological males- females don't have a Y chromosome

Question 37

If the disease recessive allele is on the X chromosome, do more males or females have the condition?

Answer 37

More males - a female would need 2 recessive alleles for the disease to show, as a dominant allele would mask it - for a male, whichever allele is on the X chromosome is inherited, so there is no change for the recessive allele to be masked

Question 38

What is embryo screening?

Answer 38

The process where a few cells are taken from an embryo produced by IVF are checked for defective genes. It doesn't alter the genetic sequence, but can detect if the developing embryo is likely to develop a genetic disorder

Question 39

Describe the process of embryo screening?

Answer 39

1) The DNA is isolated from the embryo 2) A fluorescent probe is mixed with the embryo DNA 3) The probe binds to the DNA 4) UV light is used to show if the alleles are present for the genetic disorder

Question 40

What are the advantages of embryo screening?

Answer 40

- can identify a life threatening condition - could remove some genetic disorders from the population if enough people are screened - can save a lot of money (costs a lot to raise a child with a genetic disorder)

Question 41

What are the disadvantages of embryo screening?

Answer 41

- can lead to a miscarriage - unused embryos may be destroyed - expensive - can lead to designer babies

Question 42

What is the difference between genotype and phenotype?

Answer 42

A genotype is the collection of genes an organism has. A phenotype is the physical characteristics of an organism. e.g. genotype = TT phenotype = tall