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Aqa Biology GCSE > y11 test3 > Flashcards

y11 test3 Flashcards

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1
Q

What are chromosomes?

A

Thread-like structures in the cell that contain DNA

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2
Q

What is a gene?

A

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

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3
Q

What is DNA?

A

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

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4
Q

What is genetic code?

A

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

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5
Q

What are DNA bases?

A

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

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6
Q

What is a genome?

A

The entire genetic material of an organism

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7
Q

What is the role of the DNA?

A

To code for proteins

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8
Q

What were the aims of the human genome project?

A

-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

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9
Q

What are some ethical concerns of the human genome project?

A

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

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10
Q

What is the structure of DNA?

A
  • 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
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11
Q

What are nucleotides made of?

A
  • 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
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12
Q

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

A

To protect the bases from pathogens

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13
Q

What are the 2 stages in protein synthesis?

A

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

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14
Q

What are the stages of transcription?

A

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

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15
Q

Why is only the gene needed exposed in transcription?

A

exposing all the genes isn’t energy efficient

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16
Q

Is there a ‘C’ base in RNA nucletides?

A

No- the ‘T’ is replaced with a ‘U’

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17
Q

Why does transcription take place?

A

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

18
Q

What is the exon?

A

the coding region, codes for a protein

19
Q

What is the intron?

A

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

20
Q

What are the stages of translation?

A

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

21
Q

What is a mutation?

A

A change to the base sequence of the DNA

22
Q

What causes mutations?

A

can happen spontaneously
radiation
carcinogens
inbreeding

23
Q

How do mutations happen in the exon?

A

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

24
Q

Do all mutations have a serious effect?

A

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

25
Q

What can mutations lead to in body cells or gametes?

A

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

26
Q

How do mutations happen in the intron?

A

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

27
Q

What are alleles?

A

Different forms of a gene, can be dominant or recessive

28
Q

What does homozygous mean?

A

same copies of alleles- BB or bb

29
Q

What does heterozygous mean?

A

different copies of alleles- Bb or bB

30
Q

How do you draw a genetic diagram?

A

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

31
Q

How do we draw a back cross?

A

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

32
Q

Sickle cell anemia?

A

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

33
Q

Cystic fibrosis?

A

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

34
Q

Polydactyl?

A

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

35
Q

What are the chromosomes for males and females?

A

Male - XY
Female - XX

36
Q

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

A

Biological males- females don’t have a Y chromosome

37
Q

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

A

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

38
Q

What is embryo screening?

A

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

39
Q

Describe the process of embryo screening?

A

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

40
Q

What are the advantages of embryo screening?

A
  • 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)
41
Q

What are the disadvantages of embryo screening?

A
  • can lead to a miscarriage
  • unused embryos may be destroyed
  • expensive
  • can lead to designer babies
42
Q

What is the difference between genotype and phenotype?

A

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

Aqa Biology GCSE (8 decks)

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