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IB Biology > Unit 3: Molecules and DNA > Flashcards

Unit 3: Molecules and DNA Flashcards

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1
Q

What are organic compounds?

A

Carbon containing compounds. These include glucose, fats and proteins.

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2
Q

How do carbon atoms allow a diversity of stable compounds to exist?

A

The 4 outer electrons of carbon atoms can form 4 covalent bonds with other carbon atoms or other elements. Important macromolecules are composed of long carbon chains or rings.

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3
Q

Which carbon molecules (macromolecules) make up living organisms?

A

1) Lipids
2) Carbohydrates
3) Proteins
4) Nucleic acids

These all contain carbon, hydrogen and oxygen molecules, as well as some other elements.

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4
Q

What are carbohydrates?

A

macromolecules made up of 3 elements (hydrogen, carbon and oxygen). The ratio of hydrogen to oxygen is 2:1. Carbohydrates form the most important energy source in the body.

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5
Q

What are lipids?

A

diverse group of organic compounds. These include steroids, waxes, phospholipids and triglycerides. Fatty acids are the monomers of lipids.

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6
Q

What are proteins?

A

amino acids arranged in long chains (linked through peptide bonds)

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7
Q

what are nucleic acids?

A

chains formed by nucleotides (adenine, thymine, guanine and adenosine)

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8
Q

What is glucose?

A

the building blocks of carbohydrates (such as starch and cellulose)

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9
Q

What is anabolism?

A

the synthesis of complex molecules from simple molecules including the formation of macromolecules from monomers by condensation reactions. Requires an input of energy.

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10
Q

Draw a molecular diagram of glucose.

A

check the google document.

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11
Q

Draw a molecular diagram of ribose.

A

check the google document.

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12
Q

Draw a generalised amino acid

A

check the google document.

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13
Q

What is catabolism?

A

the breakdown of complex molecules into simpler molecules including the hydrolysis of macromolecules into monomers. Energy is released in the process.

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14
Q

What is metabolism?

A

enzymatic reaction taking place inside a living organism. Metabolism = anabolism + catabolism.

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15
Q

What is hydrolysis?

A

breakdown of chemical bonds by the addition of water molecules.

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16
Q

What is condensation?

A

reaction in which 2 smaller organic molecules combine to form a larger molecule as well as a molecule of water / another simple molecule.

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17
Q

What are monosaccharides?

A

the simplest form of carbohydrates. Include ribose, glucose, fructose and galactose. 2 monosaccharides linked together create a disaccharide, and several monosaccharides linked together make a polysaccharide. Mono and disaccharides are sugars and are polar, therefore they are soluble in water.

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18
Q

How is a disaccharide produced?

A

A disaccharide is 2 monosaccharides linked together by condensation. This forms a glycosidic bond.

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19
Q

Draw a diagram of maltose being created.

A

check the google document.

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20
Q

name 3 disaccharides and how they are created.

A
  1. Sucrose → glucose + fructose
  2. Maltose → glucose + glucose
  3. Lactose → glucose + galactose
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21
Q

name 3 polysaccharides (which are made up glucose monomers)

A

Starch, glycogen and cellulose.

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22
Q

How are triglycerides formed?

A

a condensation reaction from 3 fatty acids and 1 glycerol.

23
Q

Name characteristics of triglycerides.

A

they are hydrophobic, and only soluble in organic solvents. The 2 main triglycerides are fats and oils.

24
Q

Draw a diagram of how triglycerides are formed.

A

check the google document.

25
Q

What is a phospholipid?

A

when one fatty acid in a triglyceride is replaced by a phosphate group.

26
Q

How are polypeptides formed?

A

Amino acids linked together by a condensation reaction.

27
Q

Draw a molecular diagram to show the formation of a peptide bond

A

check the google document.

28
Q

How many amino acids are there?

A

There are 20 different amino acids in polypeptides synthesised on ribosomes. They can be linked together in any sequence.

29
Q

How many different polypeptides can be made?

A

20 the the power of ‘n’ different polypeptides can be made (n = the number of amino acids per polypeptide)

30
Q

What is the function of genes?

A

a gene is a section of DNA that contains instructions for the amino acid sequence of a polypeptide. A gene normally codes for 1 polypeptide.

31
Q

Where is genetic material transcribed?

A

it is transcribed into mRNA. A protein can consist of one or more polypeptides.

32
Q

What does an amino acid sequence determine?

A

it determines the 3 dimensional conformation of a protein. The order of amino acids determines the shape and function of a protein.

33
Q

what does the R group of an amino acid determine?

A

The types of bonds and interactions with other molecules. This defines:

  • how polypeptide chains fold up in the protein and directly affect its 3 dimensional structure (conformation)
  • 1 single change in order of amino acids → can cause change in proteins conformation → change of shape, loss of function
34
Q

Define the primary, secondary and tertiary structure of an amino acid

A

Primary: the sequence of amino acids in a protein (defines all aspects of structure and function)
Secondary: folding of chains on themselves to form alpha helixes / pleated sheets
Tertiary: Polypeptide folding + coiling to make 3d shape

note: quaternary structure only occurs in proteins with 2 or more polypeptide chains

35
Q

What are globular proteins?

A

they are spherical and play an active role in a cells metabolism. They are made of complex polypeptide chains. They are usually soluble in water as the hydrophobic R group is folded into the core of the molecule.

36
Q

What are fibrous proteins?

A

They are long and threadlike. They are insoluble as the R group is exposed, and they are often found in structural parts of organisms (tendons, skin, etc)

37
Q

Describe the protein Rubisco

A
  • globular

- involved in the fixation of Co2 in choloropasts

38
Q

Describe the protein Insulin

A
  • globular
  • hormone produced by beta cells in the pancreas
  • involved in glucose uptake from the blood
39
Q

Describe the protein immunoglobin

A
  • globular
  • large Y shaped proteins
  • also called anti bodies
  • fight injections by recognising and binding to antigen molecules
40
Q

Describe the protein rhodopsin

A
  • globular
  • found in the membrane of rod cells of the retina
  • a protein linked to pigment
  • allows very low light intensities to be detected
41
Q

Describe the protein collagen

A
  • fibrous
  • structural protein found in muscles, tendons and ligaments
  • gives tensile strength
  • prevents tearing and fractures in skin and bones (respectively)
42
Q

Describe the protein spider silk

A
  • fibrous
  • produced by spiders for their webs
  • can be extended and is very resistant to breaking
43
Q

Describe the structure of DNA and RNA

A

3 parts:

  • pentose sugar (5 carbon atoms)
  • a phosphate group
  • a nitrogenous base
44
Q

What is the difference between DNA and RNA?

A
  • number of strands (DNA is double stranded, RNA is single stranded)
  • DNA has 4 bases (cytosine, adenine, thymine and guanine) and RNA has 4 bases (cytosine, adenine, uracil and guanine)
  • Type of pentose: DNA is ribose sugar without oxygen, RNA is with oxygen
  • base composition
45
Q

DNA structure and types of bonds

A

DNA is a double helix structure

  • 2 antiparallel strands of nucleotides linked by hydrogen bonding between complementary base pairs
  • cytosine and guanine (3 hydrogen bonds)
  • adenine and thymine (2 hydrogen bonds)
  • backbone connected by covalent bonds
46
Q

Draw a simple diagram of the structure of single nucleotides of DNA and RNA, using circles, pentagons, and rectangles to represent phosphates, pentoses and bases

A

check the google document.

47
Q

what are the 3 stages of transcription and translation?

A

Initiation, elongation and termination

48
Q

Describe transcription fully

A

3 stages called initiation, elongation and termination

The goal is to make an RNA copy of a gene’s DNA sequence

Initiation is the start of the process. Here, the RNA polymerase (an enzyme that synthesises a complementary RNA strand) attaches (binds) to the gene at the promoter region

The promoter region signifies the start of the gene

The RNA polymerase separates the 2 DNA strands, to provide the single strand template needed for transcription

Elongation is the second step of transcription

The RNA polymerase moves along the gene, creating a RNA molecule through adding complementary nucleotides to the DNA sequence.

This means that a- u, t-a, , and Cytosine becomes Guanine.

Termination. The terminator sequence at the end of a gene signifies to the RNA polymerase that it should stop transcribing.

The transcript is then released from the RNA polymerase, leaving behind an mRNA strand, a copy of the gene

49
Q

Describe translation fully.

A

The 3 steps are initiation, elongation and termination

Using the information of an mRNA to build a polypeptide.
Initiation: tRNA connects to the mRNA, which is in the small ribosomal subunit

This all takes place in the ribosome

The mRNA carries codons (a sequence of 3 nucleotides) and tRNA carries anticodons.

Every anticodon has a specific amino acid attached to it

The “initiator” codon attaches to the mRNA codon?

Elongation: next to the connected tRNA, a second tRNA anticodon will attach to the mRNA codon next to the original one.

The amino acid of the “initiator” tRNA is transferred to the amino acid of the tRNA that has just joined, and the formation of this peptide bond will result in a polypeptide.

A side product of this is condensation, which occurs when 2 amino acids bond.

The mRNA then translocates along the ribosome to expose another codon

The initiator tRNA is released

Another tRNA anticodon attaches to the new mRNA codon

As the mRNA continues to translocate along the ribosome, new codons appear and a larger polypeptide chain is created

Termination: a stop codon in the mRNA signals the end of the sequence

Release factors (proteins that recognise the stop codon) add a water molecule to the end of the polypeptide chain

This chain separates from the tRNA and thus a protein is released

The ribosomal subunits separate from the mRNA and the process can start again

50
Q

What is translation?

A

Translation is the synthesis of polypeptides on ribosomes

51
Q

Describe how codons are used in translation

A

Codons of three bases on mRNA correspond to one amino acid in a polypeptide

52
Q

how is the amino acid sequence of polypeptides determined?

A
  • determined by mRNA according to the genetic code
  • 64 codons can be formed using 4 bases
  • specific codons act as a signal for the protein translation machinery to start/stop
    Genetic code = degenerate (some amino acids code for more than one codon) and universal
53
Q

Deduce the DNA base sequence for the mRNA strand

A

Transcribed strand = antisense strand
Complementary to the mRNA molecule
mRNA turns adenine into Uracil, (a → u instead of a → t)

check the google document for more information

IB Biology (3 decks)

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