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Edexcel Biology B2 GCSE > B2 Topic 1 - Genes and Enzymes > Flashcards

B2 Topic 1 - Genes and Enzymes Flashcards

1
Q

3 extra things that only plant cells have

A

RIGID CELL WALL - made of cellulose, gives support to the cell
LARGE VACUOLE - contains cell sap, a weak solution of sugar and salts
CHLOROPLASTS - where photosynthesis occurs. They contain a green substance called chlorophyll

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2
Q

Bacteria cells have no…

A

Nucleus!

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3
Q

4 features of Bacteria Cells

A
  1. CHROMOSOMAL DNA (one long circular chromosome) controls the cell’s activities and replication. It floats free in the cytoplasm.
  2. PLASMIDS are small loops of extra DNA
    that aren’t part of the chromosome. Plasmids contain genes for things like drug resistance, and can be passes between bacteria.
  3. The FLAGELLUM (plural flagella) is a long, hair like structure that rotates to make the bacteria move.
  4. The cell is supported by a CELL WALL.
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4
Q

How do you calculate magnification

A

Length of image DIVIDED BY length of specimen

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5
Q

4 things animals and plant cells have in common

A

NUCLEUS - contains DNA that controls what the cell does
CYTOPLASM - gel like substance where most of the chemical reactions take place
CELL MEMBRANE - holds the cell together and controls what goes in and out
MITOCHONDRIA - these are where most of the reactions for respiration take place. Respiration releases energy so the cell can work

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6
Q

A DNA molecule has…

A

Two strands coiled together in the shape of a DOUBLE HELIX

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7
Q

How do the bases pair up

A 
Adenine and Thymine 
Cytosine and Guanine 
Remember ... 
Apples in the Tree
Cars in the Garage
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8
Q

The base pairs are joined together by…

A

Weak hydrogen bonds

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9
Q

A gene is…

A

A section of DNA, and the sequence of bases in the gene code for a specific protein

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10
Q

Who discovered the structure of DNA

A

Rosalind Franklin
Maurice Wilkins
James Watson
Francis Crick

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11
Q

What did Rosalind Franklin and Maurice Wilkins work out

A

They worked out that DNA had a HELICAL STRUCTURE by directing beams of X-RAYS onto CRYSTALLISED DNA and looked at the patterns the X-rays formed as they bounced off

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12
Q

What did James Watson and Francis Crick do

A

They used the ideas of Franklin and Wilkins, along with the knowledge that the amount of adenine + guanine MATCHED the amount of thymine + cytosine, to make a MODEL of the DNA molecule where all the pieces fitted together

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13
Q

Explain how you can do a practical to extract DNA from cells

A

1) Chop up some onion and put it in a beaker containing a solution of DETERGENT and SALT. The detergent will break down the cell membranes and the salt will make the DNA stick together.
2) Put the beaker in a WATER BATH at 60*C for 15 minutes - this denatures enzymes that could digest the DNA and helps soften the onion cells.
3) Put the beaker in ICE to cool the mixture down - this stops the DNA from breaking down.
4) Once the mixture is ice cold, put it in a BLENDER for a few seconds to break open the cell walls and release the DNA.
5) Cool the mixture down again, then FILTER it to get the froth and big bits of cell out.
6) Gently add some ice-cold ALCOHOL to the filtered mixture. The DNA will start to come out of the solution as it is not soluble in cold alcohol. It will appear as a stringy white substance.

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14
Q

A gene codes for…

A

A specific protein

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15
Q

How many amino acids are there

A

20

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16
Q

Each set of three bases (called a triplet) codes for a…

A

Particular amino acid

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17
Q

What happens in Transcription

A

1) DNA unzips
2) RNA polymerase builds mRNA using the DNA as a template
3) DNA zips back up again

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18
Q

What happens in Translation

A

1) mRNA leaves the nucleus via the nuclear pores
2) The mRNA is latched onto by a ribosome
3) The ribosome helps ensure the correct tRNA (t for transfer) molecule joins to the mRNA
4) The anticodon on tRNA has to be complementary to the mRNA codon
5) The amino acids on two transfer RNA’s come together and a peptide bond forms between them
6) The ribosome moves along the mRNA molecule building up the polypeptide chain

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19
Q

Harmful mutations could cause

A

A genetic disorder such as Cystic Fibrosis

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20
Q

A beneficial mutation could

A

Produce a new characteristic that is beneficial to an organism e.g. a mutation in genes on bacterial plasmids can make them resistant to antibiotics

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21
Q

An enzyme is

A

A biological catalyst

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22
Q

A catalyst is

A

A substance which INCREASES the speed of a reaction, without being CHANGED or USED UP in the reaction

23
Q

Examples of where enzymes are used

A

1) DNA replication - enzymes help copy a cell’s DNA before it divides by mitosis or meiosis
2) Protein Synthesis - enzymes hold amino acids in place and form bonds between them
3) Digestion - various enzymes are secreted into the gut to digest different food molecules

24
Q

Enzymes have a _______________ mechanism

A

Lock and key

25
Q

Iodine turns ______ when starch is present

A

Blue/Black

26
Q

If it gets too hot, enzymes will …

A

Denature

27
Q

The optimum temperature for most human enzymes is about..

A

37* C

28
Q

If the PH is too high or low then the enzyme

A

Denatures

29
Q

The optimum PH for most enzymes is

A

7 (BUT NOT ALWAYS!)

30
Q

Pepsin is used to

A

Break down proteins in the stomach. It works best at PH 2 which means it’s well-suited to the acidic conditions in the stomach

31
Q

Substrate concentration affects rate of reaction

A

Up to a point!

32
Q

What was the idea behind the Human Genome Project

A

To map the 25 000 (or so) human genes

33
Q

What is good about the Human Genome Project

A

It helps….

1) Predict and prevent diseases
2) Develop new and better medicines
3) Accurate diagnoses
4) Improve forensic science

34
Q

Bad stuff about the Human Genome Project

A

1) Increased stress
2) Gene-ism
3) Discrimination by employers and Insurers

35
Q

Basic idea of Genetic Engineering

A

1) A useful gene is “cut” out from one organism’s chromosome using restriction enzymes
2) Enzymes and then used to cut another organism’s chromosome and then to insert the useful gene
3) This technique produces genetically modified (GM) organisms

36
Q

Use of GM organisms:

Reducing vitamin A deficiency

A

1) Beta-carotene is used by our bodies to make vitamin A. Vitamin A deficiency is a big problem in parts of South Asia and Africa - up to 500 000 children per year go blind due to vitamin A deficiency.
2) Golden Rice is a variety of GM rice. It contains 2 genes from other organisms which together enables the rice to produce beta-carotene.
3) So growing Golden Rice can mean fewer people will suffer from vitamin A deficiency.

37
Q

Use of GM organisms:

Producing human insulin

A

1) The human insulin gene can be inserted into bacteria to produce human insulin.
2) Lots of human insulin can be produced quickly and cheaply to treat diabetes.

38
Q

Use of GM organisms:

Increasing crop yield

A

1) GM crops have had their genes modified, e.g. to make them resistant to herbicides
2) Fields of these crops can be sprayed with a herbicide and all the plants except the GM crops are killed. This can increase the yield of the crop, making more food

39
Q

Why are some people worried about genetic engineering

A

1) Some people say that growing GM crops will affect the number of weeds and flowers and therefore wildlife that usually lives in and around the crops - reducing biodiversity
2) Not everyone is convinced the GM crops are safe
3) A big concern is that transplanted genes may get out into the natural environment. For example, the herbicide resistance gene may be picked up by weeds, creating a new ‘superweed’ variety

40
Q

Mitosis is used for

A

Growth and Repair

41
Q

Human body cells are..

A

Diploid! (23 pairs of chromosomes)

42
Q

How does mitosis work and when is it used

A

Mitosis is used in growth/repair/asexual reproduction/in body cells
It created 2 daughter cells, genetically identical to the parent cell
The daughter cells are diploid
The parent cell replicates chromosomes then divides

43
Q

How does meiosis work and when is it used

A

Meiosis is used to make gametes
It takes place in reproductive organs/ovaries/testes
The parent cells are diploid
They replicate their chromosomes
2 divisions
Makes 4 daughter cells
Daughter cells are haploid and show genetic variation

44
Q

Cloning is a type of

A

Asexual reproduction

45
Q

How does cloning work

A

1) Take an unfertilised egg and remove its nucleus (the egg cell is enucleated)
2) A nucleus is taken from an adult body cell e.g. Skin cell. This is a diploid nucleus containing the full number of chromosomes
3) The diploid nucleus is inserted into the ‘empty’ egg cell
4) The egg cell is then stimulated by an electric shock - this makes it divide by mitosis
5) When the embryo is a ball of cells, it’s implanted into an adult female (the surrogate mother) to grow into a genetically identical copy of the original adult body cell

46
Q

Uses of cloning

A

1) Cloning mammals could help with the shortage of organs for transplants. For example, genetically-modified pigs could help provide suitable organs for humans. If it is successful, then cloning these pigs could help meet the demand for organ transplants
2) The study of animal clones could lead to greater understanding of the development of the embryo, and of ageing and age-related disorders
3) Cloning could also help preserve endangered species

47
Q

Issues surrounding cloning

A

1) Leads to a reduced gene pool
2) Cloned mammals may not live as long
3) The cloning process often fails
4) Clones are often born with genetic defects
5) Cloned mammals’ immune systems are sometimes unhealthy - so they suffer from more diseases

48
Q

Embryonic stem cells can turn into ..

A

ANY type of cell

49
Q

The process of stem cells becoming specialised is called..

A

Differentiation

50
Q

In most animal cells, the ability to differentiate is lost at an early age, but lots of plants…

A

Don’t ever lose this ability!

51
Q

Adult humans only have stem cells in certain places like

A

the bone marrow. These stem cells aren’t as versatile as the stem cells in embryos - they can only differentiate into certain types of cell

52
Q

Stem cells may be able to cure…

A

many diseases! E.g. Sickle cell anaemia can sometimes be cured with a bone marrow transplant

53
Q

Why are some people against embryonic stem cell research

A

They argue that human embryos shouldn’t be used for experiments because each one is a potential human life. They say that scientists should find other sources of stem cells

54
Q

Why are some people for embryonic stem cell research

A

They believe the aim of curing patients who are suffering should be more important than the potential life of the embryos. They point out that the embryos used are often unwanted ones from fertility clinics- if they weren’t used for research they would probably be destroyed

Edexcel Biology B2 GCSE (3 decks)

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