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A2 Biology > Topic 6 > Flashcards

Topic 6 Flashcards

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1
Q

Name two conventional methods for body identification.

A

Fingerprint and dental records.

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2
Q

What are the blocks of DNA that don’t code for proteins called?

A

Introns.

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3
Q

What are the blocks of DNA that code for proteins called?

A

Exons.

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4
Q

How does PCR create copies of DNA?

A
  • The DNA strand to be copied is added to a PCR machine
  • DNA polymerase is added to split the chain, as well as nucleotide bases and a primer
  • The machine raises and lowers the temperature in order for the strand to be split and copied
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5
Q

Which process can be used to separate the DNA fragments produced by PCR?

A

Gel electrophoresis:

  • The DNA sample is placed into wells in agarose gel
  • The gel is submerged in a buffer solution and has an electric current run through it
  • Shorter strands to pass through the gel quicker than the longer strands
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6
Q

How can body temperature be used to determine time of death?

A

The normal human body temperature is between 36.2 and 37.6 degrees Celsius, but after death the body begins to cool because of a lack of heat-producing reactions.

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7
Q

Which factors can affect post-mortem cooling of the body?

A

Body size Body position Clothing Air movement Humidity Temperature of surroundings

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8
Q

How can rigor mortis be used to determine time of death?

A

After death, body muscles totally relax then stiffen, known as rigor mortis. The rigor mortis passes after a period of time and the muscles relax.

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9
Q

What sequence of events happens in the muscles after death?

A
  • Muscles become oxygen-deprived and oxygen-dependent reactions stop
  • Cell respiration becomes anaerobic and lactic acid is produced
  • Cell pH falls, inhibiting enzymes and anaerobic respiration
  • ATP needed for muscle contraction are no longer produced so bonds between muscle proteins become fixed
  • The proteins can no longer move over each other, so the muscles and joints become fixed
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10
Q

Define autolysis.

A

When the body’s enzymes begin breaking down cells after death.

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11
Q

What are the signs of decomposition?

A
  • Putrefaction (skin discolouration)
  • Bloating
  • Deflation
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12
Q

Which temperatures is the rate of decomposition highest between?

A

21 and 28 degrees Celsius

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13
Q

How can entomology be used to determine time of death?

A

The stage of life the insects that have infested a body are in can be used to estimate time of death.

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14
Q

What are the features of bacteria?

A
  • Capsule
  • Cell wall
  • Cell surface membrane
  • Ribosomes
  • Flagella
  • Pili
  • Mesosomes
  • Plasmids
  • Circular DNA
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15
Q

What are the features of viruses?

A
  • Protein coat
  • Nucleic acid (DNA or RNA)
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16
Q

How do viruses reproduce?

A
  • A virus attaches to a host cell
  • The virus inserts the viral nucleic acid
  • The nucleic acid replicates
  • Viral protein coats are synthesised, forming new virus particles
  • The new virus particles are released due to cell lysis
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17
Q

What is lysozyme?

A

An enzyme used to kill bacteria by breaking down cell walls - is found in tears, saliva and nasal secretions.

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18
Q

Outline the inflammatory response.

A
  • An injury enables microbes and foreign material to enter the body
  • A blood clot seals the wound
  • Damaged white blood cells and mast cells in the connective tissue release chemicals such as histamine
  • The chemicals cause the arterioles to dilate to increase blood flow at the infected site
  • Histamines increase the permeability of the arterioles, causing plasma, white blood cells, and antibodies to leak into the tissue to cause oedema (swelling) and attack the infecting microbes
19
Q

Which cells are phagocytes?

A

Neutrophils and macrophages.

20
Q

How do phagocytes engulf bacteria?

A
  • The bacterium is engulfed by the phagocyte
  • The bacterium is enclosed inside a vacuole
  • Lysosomes fuse with the vacuole to release lysozyme to destroy the foreign material
21
Q

What is interferon?

A

A protein produced by virus-infected cells to inhibit viral protein synthesis in surrounding cells.

22
Q

What are lymphocytes?

A

White blood cells that help defend against specific diseases.

23
Q

What are the two main types of lymphocyte?

A

B cells and T cells.

24
Q

What is the response by lymphocytes called?

A

Specific immune response.

25
Q

What is the function of B cells?

A

B cells secrete antibodies in response to antigens, with each B cell producing one type of antibody which binds to a specific antigen.

26
Q

Where are B cells produced?

A

Bone marrow.

27
Q

Outline the structure of an antibody.

A
  • Antigen binding sites (differing structure due to different amino acid sequences)
  • Disulphide bonds to hold the polypeptide chains together
28
Q

Where are T lymphocytes produced and matured?

A

Produced in bone marrow and mature in the thymus gland.

29
Q

What is the function of T helper cells?

A

When activated, they stimulate B cells to divide and produce antibodies, and stimulate the activity of phagocytes.

30
Q

How do macrophages become APCs (antigen-presenting cells)?

A

Protein fragments from the engulfed biological material become attached to proteins in the macrophage. These proteins are incorporated into the macrophage’s cell surface membrane and act as non-self antigens.

31
Q

How do APCs activate T helper cells?

A

CD4 receptors on the surface of T helper cells attach to antigens on the surface of APCs, causing the T helper cell to divide and produce an active T helper cell clone and a T memory cell clone.

32
Q

Describe the clonal selection of B cells.

A

When a T helper cell CD4 receptor attaches to an antigen on the surface of an APC, cytokines are produced to stimulate the B cell The B cell divides to produce B memory cells and B effector cells B effector cells differentiate into plasma cells which secrete antibodies

33
Q

What is the primary immune response?

A

The 10-17 days it takes for the sufficient production of antibody-producing cells from clonal selection.

34
Q

What is the role of T killer cells?

A

T killer cells with complementary receptors bind to antigens displayed on APCs The T killer cells are stimulated by cytokines from T helper cells to divide into active and memory T killer cells Activated T killer cells release enzymes which create pores in the infected cell, causing lysis When the pathogens are released from the infected cells, they are labelled by antibodies for destruction by macrophages.

35
Q

What is the secondary immune response?

A

If infected by the same pathogen again, B memory cells produced in the primary response can differentiate immediately to produce plasma cells and release antibodies.

36
Q

Which bacterium is Tuberculosis caused by?

A

Mycobacterium tuberculosis.

37
Q

How does the M. tuberculosis bacteria evade the immune system?

A

The bacteria have thick waxy walls to resist phagocytosis TB bacteria can survive and breed inside macrophages

38
Q

How can HIV spread?

A
  • Unprotected sex
  • Sharing needles
  • Maternal transmission from mother to unborn child or breastmilk
39
Q

Outline how HIV invades T helper cells.

A
  • gp120 glycoproteins on the virus surface bind to CD4 recptors on the cell
  • They then bind with a second CD4 receptor to allow the viral envelope to fuse with the cell’s surface membrane
  • Viral RNA is inserted into the cell
40
Q

Outline how HIV hijacks a T helper cell’s protein synthesis.

A
  • Reverse transcriptase is used to reverse normal transcription
  • DNA is produced from the viral RNA template
  • The HIV DNA is intetgrated into the host cell’s DNA using integrase
  • Once the HIV is integrated into the host cell’s genome, it can be transcibed and translated to produce new viral proteins
41
Q

Outline transcription.

A
  • RNA polymerase attaches to the DNA
  • The hydrogen bonds between base pairs break and the DNA unwinds
  • RNA nucleotides are paired with DNA bases to form an mRNA molecule
  • The mRNA molecule leaves the nucleus through a nuclear pore
42
Q

Outline translation.

A
  • mRNA attaches to the surface of a ribosome
  • tRNA molecules carry complementary anticodons to the mRNA codons
  • The ribosome holds the mRNA and tRNA while peptide bonds form between the amino acids in a condensation reaction
  • Once the peptide bond has formed, the ribosome moves along the mRNA to reveal a new codon at the binding site
  • The process is repeated until a stop codon is reached
43
Q

Why does the immune system of a HIV patient become deficient?

A

T killer cells destroy the infected T helper cells.

44
Q
A

A2 Biology (6 decks)

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