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Biology A Level > Protein Synthesis > Flashcards

Protein Synthesis Flashcards

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1
Q

How is RNA different from DNA?

A
  • RNA consists of 1 polynucleotide strand which is much shorter
  • the 5-carbon sugar is RIBOSE not DEOXYRIBOSE
  • the base THYMINE is replaced by URACIL (but like thymine can pair with adenine)
  • RNA does not twist up to form a helical strand
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2
Q

What are proteins? How are they made?

A

Proteins (polypeptides) are large molecules called polymers

They are made by joining together many smaller subunits called AMINO ACIDS (monomers)

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3
Q

How many different types of amino acids are there?

A

There are 20 different types of amino acids that can be reassembled together in different orders to make the proteins we need

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4
Q

What sequence determines the sequence of bases in DNA ?

A
  • it is the sequence of bases in DNA which determines the sequence of amino acids in the proteins the cell makes
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5
Q

What structure in a protein does the sequence of amino acids form?

A
  • the sequence of amino acids in proteins are known as the primary structure
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6
Q

What is a gene?

A
  • a gene is a length of DNA (a sequence of nucleotide bases) that codes for one or more polypeptide
  • gene are a unit of heredity
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7
Q

How many genes are there in a human genome?

A
  • in the human genome there are about 25 000 genes
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8
Q

What is a genome?

A
  • a genome is an organisms complete set of DNA inc all of its genes
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9
Q

Where are most genes found?

A
  • most of the genes are found on the linear chromosomes within the nucleus
  • each gene occupies a specific place/locus on the chromosome
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10
Q

Give examples of polypeptides that genes can code for:

A
  • structural proteins e.g. COLLAGEN (skin/bones) KERATIN (hair/nails)
  • immunoglobulins (ANTIBODY)
  • HAEMOGLOBIN
  • channel proteins
  • TUBULIN proteins in the cytoskeleton
  • Antigens and cell surface receptors
  • enzymes
  • actin and myosin in muscle cells
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11
Q

Because genes code for enzymes what does this mean?

A
  • since genes code for enzymes, they are involved in the CONTROL of all METABOLIC PATHWAYS
    And thus in the synthesis of all non-protein molecules found in cells
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12
Q

What provides a code for the construction of a polypeptide or protein?

A
  • the SEQUENCE OF NUCLEOTIDE BASES on a gene (length of DNA) provides a code with instructions for the construction of a polypeptide/protein
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13
Q

What is one of characteristics the genetic code has?

A

The genetic code is a TRIPLET CODE:

  • A Sequence of 3 nucleotide bases e.g. GTA code for an AMINO ACID
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14
Q

Why are there 64 different possible triplet sequences?

A
  • there are 4 bases grouped in 3
    So the number of different triplet sequences is 4 to the power of 3 or 64
  • as there are only 20 amino acids used for protein synthesis this is more than enough
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15
Q

What is another characteristic the genetic code has?

A
  • the genetic code is a degenerate code
  • all amino acids except METHIONINE have more than ONE CODE

Note: methionine is always the first amino acid in every protein

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16
Q

Do all codes correspond to a particular amino acid?

A

Some codes DO NOT correspond to a particular amino acid

Instead they indicate STOP at the end of the polypeptide Chain

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17
Q

Another characteristic of the genetic code is that it is WIDESPREAD BUT NOT UNIVERSAL:

A
  • the genetic code is not universal universal but is widespread

The base sequence TCT codes for the amino acid serine in any organism but there are some base sequences which won’t code for particular things in certain organisms

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18
Q

Another characteristic of the genetic code is that its non -overlapping:

A

Genetic code non-overlapping
- the genetic code is read starting from a fixed point in groups of 3 bases
If a base is ADDED or DELETED then it causes a FRAME SHIFT to every base triplet after that and hence every amino acid code is changed

19
Q

Where are genes found?

A
  • genes are found on chromosomes in the cell nucleus
20
Q

Where are proteins assembled?

A
  • Proteins are assembled in the cytoplasm at ribosomes
21
Q

What is the problem with genes being on chromosomes in the cell nucleus but proteins being assembled in the cytoplasm at ribosomes?

A
  • DNA is TOO large to pass directly out of the nucleus through NUCLEAR PORES
22
Q

What is the solution to DNA being too large to pass out through nuclear pores:

A
  • a copy of the genetic code has to be made which can pass through a pore in the nuclear envelope to the cytoplasm
23
Q

What is the name of the genetic code which can pass through a pore in the nuclear envelope?

A
  • messenger RNA mRNA is the copy of the genetic code
24
Q

Why is the first stage of protein synthesis?

A
  • the first stage of protein synthesis is TRANSCRIPTION

- during TRANSCRIPTION messenger RNA mRNA molecule is made

25
Q

Describe the stages of transcription:

A
  1. A gene to be transcribed unwinds and unzips
    - this unwinding and unzipping is caused by an enzyme called DNA HELICASE which BREAKS the HYDROGEN BONDS between complementary base pairs
  2. one strand (the template/reference strand) of the DNA is then used as a TEMPLATE
  3. The other strand not used as a template is known as the CODING STRAND
  4. Free RNA nucleotides in the nucleus then line up alongside the TEMPLATE STRAND and bond to their COMPLEMENTARY EXPOSED BASE
    - this process is catalysed by the enzyme RNA POLYMERASE
  5. The mRNA produced is COMPLEMENTARY to the nucleotide base sequence on the template strand of the DNA
    - the mRNA is therefore a copy of the base sequence on the coding strand of the length of DNA
26
Q

After mRNA has been produced by transcription where is the mRNA molecule released to ?

A

The mRNA is released from the DNA and passes OUT of the NUCLEUS though a PORE in the NUCLEAR ENVELOPE–> a RIBOSOME

Some ribosomes are free in the cytoplasm but many are bound to the rough endoplasmic reticulum

27
Q

What is the second stage of protein synthesis called?

A

TRANSLATION is the second stage of protein synthesis

28
Q

Why does TRANSLATION need to happen?

A
  • TRANSLATION is the stage during protein synthesis in which AMINO ACIDS are ASSEMBLED INTO A POLYPEPTIDE
29
Q

How many types of mRNA are there?

A

There are 3 types of mRNA:

  • mRNA
  • tRNA
  • rRNA
30
Q

What is mRNA?

A

mRNA contains a sequence that is complementary to the nucleotide base sequence on the template strand of the DNA

31
Q

What is the name given to each group of 3 bases on the mRNA molecule?

A

Each group of three bases on the mRNA molecule is called a codon
Each codon stands for a particular amino acid

32
Q

What is the function of some particular codons?

A

Some CODONS also act as STOP and START CODONS

33
Q

What sequence denotes methionine and can indicate that this where the amino acid chain should begin?

A

The sequence AUG denotes methionine and can indicate that this is where the amino acid chain should be begun

34
Q

What does rRNA stand for?

A

RIBOSOMAL RNA

35
Q

Where are ribosomes assembled?

A

Ribosomes are assembled in the NUCLEUS of EUKARYOTE CELLS from ribosome RNA (rRNA and protein)

36
Q

How many subunits are ribosomes made up of?

A
  • ribosomes are made up of 2 subunits (large and smaller which fit together)
37
Q

Why is there a groove between the 2 subunits?

A

Between the 2 subunits there is a GROOVE into which the length of mRNA (which code for the sequence of amino acids) can fit
The RIBOSOME can then move along the mRNA which can slide through RIBOSOMAL GROOVE
Reading the code and assembling and assembling the amino acids in the correct order to make a protein

38
Q

What does tRNA stand for?

A

TRANSFER RNA

39
Q

Where is tRNA made and where does it travel to?

A

tRNA is also made in the NUCLEUS then passes out into the CYTOPLASM

40
Q

What is tRNA?

A
  • tRNA are lengths of RNA that fold into HAIRPIN SHAPES and have 3 EXPOSED BASES AT ONE END where a PARTICULAR AMINO ACID can bind
  • at the other end of the molecule are 3 UNPAIRED bases known as ANTICODON
41
Q

What can each ANTICODON temporarily do?

A

Each ANTICODON can temporarily bind with its complementary codon on the mRNA strand

42
Q

How is a polypeptide assembled?

A

-1. A molecule of mRNA binds to a ribosome
- 2 CODONS are attached to a small unit of a ribosome and are exposed to the large subunit
- using ATP energy and an ENZYME a tRNA with METHIONINE and the ANTICODON UAC forms hydrogen bonds with this codon
2. A second tRNA with a different amino acid binds to the second exposed CODON with its complementary CODON
3. A peptide bond, forms between the 2 adjacent amino acids
An ENZYME in the small ribosomal subunit catalyses the reaction
4. The RIBOSOME now moves along the mRNA reading the next CODON
- a third tRNS brings another amino acid. And a peptide bond forms between it an the dipeptide
5. The polypeptide chain grows until a STOP CODON is reached

43
Q

Where is DNA NOT inside a prokaryotes?

A

In PROKARYOTES the DNA is N.O.T inside the NUCLEUS

Therefore TRANSLATION begins as soon as some mRNA has been made

Biology A Level (36 decks)

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