D1.2 Protein synthesis

exams 2025 D1.2.1 - D1.2.19 SL & HL UNFINISHED!!!

number of strands : 1 & 2

type of sugar: ribose & deoxyribose

base differences: uracil & thymine

What are the differences between RNA and DNA?

the synthesis of RNA, using DNA as a template

• The enzyme RNA polymerase transcribes DNA to RNA.

Define Transcription

Occurs in nucleus of the cell

1. RNA Polyamersae attaches to the begging of a gene on DNA

2. RNA Polymerase seperates the two DNA strands

3. An mRNA molecule (produced on the template DNA strand) uses the enzyme to link RNA nucleotides into a single polynucleotide (condensation reaction)

4. RNA polymerase uses complementry base pairings to pair DNA + RNA nucleotides

5. RNA Polymerase reaches the end of the gene, the mRNA molecule is released

Transcription Steps:

DNA Base	RNA Base
Adenine (A)	Uracil (U)
Guanine (G)	Cytosine (C)
Cytosine (C)	Guanine (G)
Thymine (T)	Adenine (A)

• held together by hydrogen bonds

What are the complementry base pairs of DNA and RNA, what are they held together by?

strong covalent bonds between nucleotides

Why is DNA a stable molecule?

non-reproductive cells in organism

What are somatic cells?

as they don’t divide, single DNA strands can be used as a template for transcribing a base sequence, without the DNA base sequence changing, such sequences must be conserved throughout the life of a cell

What must be conserved in somatic cells?

• Transcription

• Translation

What two stages does protein synthesis consist of?

the synthesis of polypeptides (proteins) by ribosomes, using genetic code of mRNA

Define Translation

process where genetic information in a gene is used to synthesize a functional polypeptide

Define Gene Expression

gene must be transcribed to mRNA mRNA can be translated by a ribosome

• If transcription doesn’t occur, neither can translation

Order in protein synthesis

by regulating transcription of genes

How can gene expression be switched on or off?

ribosomes require messenger RNA (mRNA) and transfer RNA (tRNA)

What is required for translation?

• mRNA brings the genetic code to the ribosome/containas genetic form of codons

• tRNA brings amino acids to the ribosome

Function of mRNA and tRNA

organells found in cells which translate genetic code of mRNA to a polypeptide

What are ribosomes?

• small subunit

• large subunit

What are ribosomes composed of?

sequence of three nucleotides that code for an amino acid

What are codons?

ribosomes use a sequence of codons on mRNA to determine the sequence of amino acids in a polypeptide

What determines the sequence of a polypeptide?

• two tRNA molecules can bind simoulanously to the large subunit oif

• mRNA binds to small subunit of ribosome to initiate translation

• transfers amino acids from cytoplasm to the ribosome

• tRNA have an anticodon which binds to mRNA codons

• the binding of mRNA and the tRNA’s anticodeons in the ribosome by complamentry base pairing ensure the correct sequence of amino acids are synthesized

WHat are the steps of translation?

20 found in proteins

how many amino acids are found in living organisms?

by combining nucleotides into sequences of 3, producing in total 64

how does the genetic code code for them?

20

For how many different amino acids can these codons code for?

• three

• don’t code for amino acids and terminate translation

How many STOP codons are there? What do they do?

more than one codon may code for the same amino acid

Define degenerate

whoops! describe movement of ribosome

polypeptide chain grows

didnt do d1.2.10

change to the DNA sequence of an organism

Define Mutation

a single substitution mutation to a nucleotide in the alpha globin molecule in hemoglobin

What can cause sickle cell anemia?

invloves swapping one nucleotide for another

Define base substitutuion mutation

causes the shape of RBC to change into a sickle shape which may block small blood vessels

Why is sickle cell anemia bad?

regulator proteins which attach to the promoter region

WHat are transcription factors?

wether RNA polymerase can attach to the promoter region, controlling gebe expression

WHat do transcription factors control?

• gene sequences that code for mRNA

• expressed as functional polypeptides

What are coding sequences of DNA?

• sections that don’t code for functional polypeptides

• some sections have functions like:

  1. controlling gene expression(can decide the transcription of genes)

  2. genes for rRNA and tRNA

  3. telomeres

What are non-coding sequences of DNA?

repeptative base sequences at the ends of chromosomes

WHat are telomeres?

come bac to d1.2.14

sections of DNA that don’t code for a protein and interrupt gene sequences

what are Introns?

sections of DNA and RNA that do code for proteins

what are Exons?

they’re removed from mRNA

What happens to introns after transcription?

scray tf

skip D1.2.15

• Aminoacyl site

• Peptidyl site

• Exit site

What are th A, P, E site?

tRNA brings new amino acids to be added to the elongating polypeptide chain

Function of A site?

• holds the tRNA

• peptide bond forms between amino acids in A and P site which releases tRNA into E site

Function of P site?

after tRNA enters E site it’s released from the ribosome

Function of E site?

• Initiation

• Elongation

• Termination

What are the three stages of Translation?

d1.2.17 look through it bb

must be modified

What must happen to polypeptides before they can function?

• single popypeptide removed through endoplasmic reticulum to create pro-insulin

• sent and packaged into secretory vesel

• ALPHA & BETA chains join by dislulfide bonds to form functional insulin

• insulin secreted into bloodstream

WHat must happen to pre-insulin so that it’s functional?

entire complement of proteins that is expressed by a cell or organism

What are Proteasomes?

• broken down to amino acids through proteasomes

• hydrolysis reaction

What happens to proteins that are no longer required by cell?

recylced to synthesized proteins that are required by cell

What happens with these amino acids?